| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | February 3, 2004 |
| PATENT TITLE |
Mutant presenilin 1 polypeptides |
| PATENT ABSTRACT | The present invention provides mutant presenilin 1 and presenilin 2 polpeptides and polynucleotides encoding the polypeptides and methods for their production by recombinant and PCR techniques are disclosed. Methods for utilizing the mutant polypeptides in screens for inhibitors of activity are also disclosed |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | June 29, 2001 |
| PATENT REFERENCES CITED |
Ngo et al. (1995) The Protein Folding Problem and Tertiary Structure Prediction. 433-506.* Jobling et al, Mol. Microbiol., 1991, 5(7):1755-67.* Skolnick and Fetrow (2000) From Genes to Protein Strucuture and Function: Novel Applications of Compuational Approaches in the Genomic Era. Trends in Biotech 18(1); 34-39.* Wells, J.A. Additivity of Mutational Effects of Proteins (1990) Biochemistry 29(37): 8509-8517.* Bork (2000) Powers and Pitfalls in Sequence Analysis: The 70% Hurdle, Genome Research 19: 398-400.* Doerks (1998) Protein Annotation: detective work for function prediction. TIG 14(6): 248-250.* Smith and Zhang (1997) The Challenges of genome sequence annotation of "The Devil is in the details". Nature Biotechnology 15: 1222-1223.* Brenner (1999) Erros in genome annotation. TIG 15(4): 132-133.* Bork and Bairoch (1996) Go Hunting in sequence databases but watch out for the traps. TIG 12(10): 425-427.* Russo C; Schettini G; Saido TC; Hulette C; Lippa C; Lannfelt L; Ghetti B; Gambetti P; Tabaton M; Teller JK, reply: Alzheimer's disease Molecular consequences of presenilin-1 mutation, Nature Jun 7, 2001; 411 (6838): 655. Ausubel, et al., ed., in Short Protocols in Molecular Biology, 2nd Edition, John Wiley & Sons, publishers, p. 16-49, 1992. Borchelt et al., Familial Alzheimer's Disease-Linked Presenilin 1 Variants Elevate A.beta.1-42/1-40 Ratio in Vitro and in Vivo Neuron 17: 1005-1013, 1996. Citron, M. et al., Mutation of the beta-amyloid precursor protein in familial Alzheimer's disease increases beta-protein production. Nature 360, 672-674 (1992). Citron, M.; Westaway, D.; Xia, W.; Carlson, G.; Diehl, T.; Levesque, G.; Johnson-Wood, K.; Lee, M.; Seubert, P.; Davis, A.; Kholodenko, D.; Motter, R.; Sherrington, R.; Perry, B.; Yao, H.; Strome, R.; Lieberburg, I.; Rommens, J.; Kim. S.; Schenk, D.; Fraser, P., St George Hyslop, P.; Selkoe, D.J.: Mutant presenilins of Alzheimer's disease increase production of 42-residue amyloid beta-protein in both transfected cells and transgenic mice. Nature Med. 3: 67-72, 1997. Cosman et al., High Level Stable Expression of Human Interleukin-2 Receptors in Mouse Cells Generates Only Low Affinity Interleukin-2 Binding Sites. Molecular Immunology. 23:935, 1986. Cosman et al., Cloning Sequence and Expression of Human Interleukin-2 Receptor. Nature 312:768, 1984. Creighton, TE, Proteins--Structure and Molecular Properties, 2nd Ed. W. H. Freeman and Company, New York, 1993. De Strooper B, Saftig P, Craessaerts K, Vanderstichele H, Guhde G, Annaert W, Von Figura K, Van Leuven F. Deficiency of presenilin-1 inhibits the normal cleavage of amyloid precursor protein. Nature. 39(6665):387-90 Jan. 22, 1998. Gandy S; Naslund J; Nordstedt C, Alzheimer's disease Molecular consequences of presenilin-1 mutation, Nature 411 (6838): 654-5 Jun. 7, 2001. Glenner GG; Wong CW, Alzheimer's disease and Down's syndrome: sharing of a unique cerebrovascular amyloid fibril protein., Biochem Biophys Res Commun Aug. 16, 1984; 122 (3): 1131-5. Gluzman et al., SV40-Transformed Simian Cells Support the Replication of Early SV40 Mutants. Cell 23:175, 1981. Goate, A.; Chartier-Harlin, M.-C.; Mullan, M.; Brown, J.; Crawford, F.; Fidani, L.; Giuffra, L.; Haynes, A.; Irving, N.; James, L.; Mant, R.; Newton, P.; Rooke, K.; Roques, P.; Talbot, C.; Pericak-Vance, M.; Roses, A.; Williamson, R.; Rossor, M.; Owen, M.; Hardy, J.: Segregation of a missense mutation in the amyloid precursor protein gene with familial Alzheimer's disease. Nature 349: 704-706, 1991. Hardy, John. Framing .beta.-amyloid. Nature Genetics. 1:233-234, 1992. Hogan et al., Manipulating The Mouse Embryo, Cold Spring Harbor Laboratory Press, 1986. Kang et al. The Precursor of Alzheimer's Disease amyloid A4 Protein resembles a cell-surface receptor. Nature 325:733-736, 1987. Kimberly, WT; Xia, Weiming; Rahmati, Talat; Wolfe, Michael S; Selkoe, Dennis J., The Transmembrane Aspartates in Presenilin 1 and 2 are Obligatory for .gamma.-Secretase Activity and .beta.-Protein Generation, vol. 275, No. 5, Feb. 4, pp. 3173-3178. Journal of Biological Chemistry (2000). Kitaguchi et al. Novel Precursor of Alzheimer's Disease amyloid Protein shows Protease Inhibitory Activity. Nature 331:530-532, 1988. Kraemer et al., Genetic Manipulation Of The Early Mammalian Embryo, Cold Spring Harbor Laboratory Press, 1985. Jones and Bendig, Rapid PCR-Cloning of Full-Length Mouse Immunoglobulin Variable Regions. Bio/Technology, 9: 88, 1991. Lehninger, Biochemistry, Second Edition; Worth Publishers, Inc. NY:NY pp. 71-77, 1975. Levy-Lehad, E.; Wasco, W.; Poorkaj, P.; Romano, D. M.; Oshima, J.; Pettingell, W. H.; Yu, C.; Jondro, P. D.; Schmidt, S. D.; Wang, K.; Crowley, A. C.; Fu, Y.-H.; Guenette, S. Y.; Galas, D.; Nemens, E.; Wijsman, E. M.; Bird, T. D.; Schellenberg, G. D.; Tanzi, R.E. : Candidate gene for the chromosome 1 familial Alzheimer's disease locus. Science 269: 973-977, 1995. Li YM, Xu M, Lai MT, Huang Q, Castro JL, DiMuzio-Mower J, Harrison T, Lellis C, Nadin A, Neduvelil JG, Register RB, Sardana MK, Shearman MS, Smith AL, Shi XP, Yin KC, Shafer JA, Gardell SJ. Photoactivated gamma-secretase inhibitors directed to the active site covalently label presenilin 1. Nature. 405(6787):689-94, Jun. 8, 2000. Luckow, Verne A., and Max D. Summers, Trends in the Development of Baculovirus Expression Vectors Bio/Technology 6:47, 1988. Marambaud P; Ancolio K; Lopez-Perez E; Checler F, Proteasome inhibitors prevent the degradation of familial Alzheimer's disease-linked presenilin 1 and potentiate A beta 42 recovery from human cells.,Molecular Medicine v.4:147-157, 1998. Mehta ND, Refolo LM, Eckman C, Sanders S, Yager D, Perez-Tur J, Younkin S, Duff K, Hardy J, Hutton M. Increased Abeta42(43) from cell lines expressing presenilin 1 mutations. Annals of Neurology. 43(2):256-8, Feb. 1998. Mullan, M., Crawford, F., Axelman, K., Houlden, H., Lilius, L., Winblad, B., Lannfelt, L. A pathogenic mutation for probable Alzheimer's disease in the APP gene at the N-terminus of beta amyloid. Nature Genetics. 1, 345-347 1992. Murayama O, Tomita T, Nihonmatsu N, Murayama M, Sun S, Honda T, Iwatsubo T, Takashima A. Enhancement of amyloid 42 secretion by 28 different presenilin 1 mutations of familial Alzheimer's . Neuroscience Letters 265(1):61-63, Apr. 1999. Okayama, Hiroto, and Paul Berg, A cDNA Cloning Vector That Permits Expression of cDNA Inserts in Mammalian Cells. Molecular and Cellular Biology, 3:280, 1983. Ponte, P., et al., A new A4 Amyloid mRNA contains a Domain Homologous to Serine Proteinase Inhibitors. Nature 331:525-527, 1988. Qian S, Jiang P, Guan XM, Singh G, Trumbauer ME, Yu H, Chen HY, Van de Ploeg LH, Zheng H. Mutant human presenilin 1 protects presenilin 1 null mouse against embryonic lethality and elevates Abeta-42/43 expression. Neuron. (3):611-7 Mar. 20, 1998. Rattan et al., "Protein Synthesis: Post-translational Modifications and Aging", Ann NY Acad Sci 663:4842 1992. Rawlings N and Barrett A, "Families of Aspartic peptidases, and those of unknown catalytic mechanism," Methods in Enzymology, vol. 248, 1995; pp. 105-120. Rishton GM, Retz DM, Tempest PA, Novotny J, Kahn S, Treanor JJ, Lile JD, Citron M. Fenchylamine sulfonamide inhibitors of amyloid beta peptide production by the gamma-secretase proteolytic pathway: potential small-molecule therapeutic agents for the treatment of Alzheimer's disease. J Med Chem. 43(12):2297-9, Jun. 15, 2000. Rogaev, E. I.; Sherrington, R.; Rogaeva, E. A.; Levesque, G.; Ikeda, M.; Liang, Y.; Chi, H.; Lin, C.; Holman, K.; Tsuda, T.; Mar, L.; Sorbi, S.; Nacmias, B.; Placentini, S.; Amaducci, L.; Chumakov, I.; Cohen, D.; Lannfelt, L.; Fraser, P. E.; Rommens, J. M.; St George-Hyslop, P. H.: Familial Alzheimer's disease in kindreds with missense mutations in a gene on chromosome 1 related to the Alzheimer's disease type 3 gene. Nature 376: 775-778, 1995. Russo, C; Schettini G; Saido TC; Hulette C; Lippa C; Lannfelt L; Ghetti B; Gambetti P; Tabaton M; Teller JK, Presenilin-1 mutations in Alzheimer's disease., Nature 405 (6786): 531-2, Jun. 1, 2000. Gandy, S., Nastond, J., and Nordstedt, C. "Alzheimer's disease: Molecular consequences of presenilin-1 mutation," Nature 411, pp. 654-655 (2001). Seifter et al., Analysis for protein modifications and nonprotein cofactors, Methods in Enzymology 182:626-646, 1990. Sherrington, R.; Rogaev, E. I.; Liang, Y.; Rogaeva, E. A.; Levesque, G.; Ikeda, M.; Chi, H.; Lin, C.; Li, G.; Holman, K.; Tsuda, T.; Mar. L.; Foncin, J.-F.; Bruni, A. C.; Montesi, M. P.; Sorbi, S.; Rainero, I.; Pinessi, L.; Nee, L.; Chumakov, I.; Pollen, D.; Brookes, A.; Sanseau, P.; Polinsky, R. J.; Wasco, W.; Da Silva, H. A. R.; Haines, J. L.; Pericak-Vance, M. A.; Tanzi, R. E.; Roses, A. D.; Fraser, P. E.; Rommens, J. M.; St. George-Hyslop, P. H.: Cloning of a gene bearing mis-sense mutations in early-onset familial Alzheimer's disease. Nature 375: 754-760, 1995. Suzuki, N., et al. An increased precentage of long amyloid beta protein secreted by amilial amyloid beta protein precursor (beta APP717) mutants. Science 264, 1336-1340, 1994. Tajima K, Babich S, Yoshida Y, Dantes A, Strauss JF 3rd, Amsterdam A. The proteasome inhibitor MG132 promotes accumulation of the steroidogenic acute regulatory protein (StAR) and steroidogenesis. Federation of European Biochemical Societies Letter. 490(1-2):59-64, Feb. 9, 2001. Tanzi, Rudolph E., Protease Inhibitor Domain Encoded by an Amyloid Protein Precursor mRNA Associated with Alzheimer's Disease. Nature, 331:528-530, 1988. Wold, F., "Post-translational Protein Modifications: Perspectives and Prospects", pp. 1-12 in Postranslational Covalent Modification of Proteins, B. C. Johnson, Ed., Academic Press, New York, 1983. Xia W, Zhang J, Kholodenko D, Citron M, Podlisny MB, Teplow DB, Haass D, Seubert P, Koo EH, Selkoe DJ. Enhanced Production and Oligomerization of the 42-residue Amyloid-Protein by Chinese Hamster Ovary Cells Stably Expressing Mutant Presenilins J. Biol. Chem. 272:7977-7982, 1997. Yamatsuji, Tomoki, et al., G Protein-Mediated Neuronal DNA Fragmentation Induced by Familial Alzheimer's Disease-Associated Mutants of APP. Science 272:1349-1352, 1996. Zigmond, Bloom, Landis, Roberts, Squire, eds. "Fundamental Neuroscience," Academic Press (1999), pp. 1333-1335. |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. An isolated mutant presenilin-1 polypeptide comprising SEQ ID NO: 5 wherein residue 386 is selected from the group consisting of threonine or conservative substitutions of threonine and wherein residue 387, is selected from the group consisting of glycine or conservative substitutions of glycine and wherein said mutant presenilin-1 polypeptide preferentially modulates the processing of amyloid precursor protein to yield increased levels of A.beta..sub.1-42 relative to A.beta..sub.1-40 when compared to a wild type presenilin-1 polypeptide. 2. The isolated mutant presenilin-1 polypeptide of claim 1 wherein residue 386 is selected from the group consisting of threonine and serine. 3. The isolated mutant presenilin-1 polypeptide of claim 1 wherein residue 386 is a threonine and residue 387 is a glycine. 4. The isolated mutant presenilin-1 polypeptide of claim 1 wherein residue 386 is selected from the group consisting of threonine and conservative substitutions of threonine and wherein residue 387 is glycine. 5. The isolated mutant presenilin-1 polypeptide of claim 1 wherein residue 386 is threonine and wherein residue 387 is selected from the group consisting of glycine and conservative substitutions of glycine. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION The present invention provides mutant presenilin 1 and presenilin 2 polypeptides and polynucleotides encoding the polypeptides and methods for their production by recombinant and PCR techniques are disclosed. Methods for utilizing the mutant polypeptides in cell based and in-vitro assays for inhibitors of activity are also disclosed. BACKGROUND OF THE INVENTION Alzheimer's disease was originally thought to be a rare disorder primarily affecting only people under the age of 65. It is now recognized as the most common form of dementia, and alone is responsible for about 50% of all dementias; an additional 15-20% of dementias have combined Alzheimer's and vascular pathology. The prevalence of the Alzheimer's is directly related to age. It can occur in the fourth decade of life but is extraordinarily rare at this age. The prevalence then increases logarithmically with each succeeding decade. Over the age of 85 at least one person in four is afflicted. Because persons over the 85 form the rapidly growing portion of the population Alzheimer's disease represents a major health problem. Zigmond, et.: Fundamental Neuroscience, Academic Press, 1999. Alzheimer's disease is thought to be initiated by the deposition of amyloid plaque in cortex and hippocampus. The material deposited in plaque is proteinaceous. It consists primarily of the amyloid .beta.-peptide (A.beta.), a peptide of 39-43 amino acids which is derived from a larger precursor, the amyloid peptide precursor (APP), through the action of specific proteases. APP is a large, type-I transmembrane protein of 695-770 amino acids that is expressed by a variety of cell types including neurons, glia and somatic cells. The cleavage of A.beta. from APP is accomplished by the action of two proteolytic activities commonly denoted as beta-secretase (Asp2) and gamma-secretase. Processing at the .gamma.-secretase site is somehow dependent on presenilin-1 (as it does not occur in PS1 null embryonic neurons grown in culture, DeStrooper et al., 1997), but the protease responsible has not been identified. Deletion of the PS1 gene in mice greatly reduces gamma secretase activity. With less than 5% of the APP made by the cell processed through the amyloidogenic pathway to A.beta.. DeStrooper (1998); Qian (1998). A causative role for A.beta. peptide in Alzheimer's disease is supported by genetic studies of familial, early-onset Alzheimer's disease in which inheritance follows an autosomal dominant mode of transmission. In such patients, genetic forms of Alzheimer's disease have been associated with mutations in the APP gene (Groate et al., 1991; Mullan et al. 1992), and two related genes, presenilin-1 (PS-1; Sherrington et al., 1995) and presenilin-2 (PS-2; Levy-Lahad et al., 1995; Rogaev et al., 1995). Mutations in all three genes alter production of the A.beta. peptide in specific ways. PS1 and PS2 mutations subtly increase the production of A.beta..sub.1-42 peptide as compared to the A.beta..sub.1-40 peptide (e.g., Citron et al., 1997), Mehta et al. (1998), Murayama et al. (1999), Xia et al. (1997). A.beta..sub.1-42 is generally recognized as being more toxic to cells than A.beta..sub.1-40. Because PS1 and PS2 are intimately involved with the processing of APP both genes are attractive targets for drug screening in which aberrant APP processing is a causative or exacerbating factor. It has been postulated that both presenilin 1 and presenilin 2 have some intrinsic protease activity but this activity is so weak that designing a method of screening test agents which inhibit the intrinsic activity is problematic. The invention provides mutant presenilin 1 and presenilin 2 with enhanced proteolytic activities suitable for high throughput screening. Literature Cited 1. Citron, M. et al. Mutation of the beta-amyloid precursor protein in familial Alzheimer's disease increases beta-protein production. Nature 360, 372-374 (1992). 2. Citron, M.; Westaway, D.; Xia, W.; Carlson, G.; Diehl, T.; Levesque, G.; Johnson-Wood, K.; Lee, M.; Seubert, P.; Davis, A.; Kholodenko, D.; Motter, R.; Sherrington, R.; Perry, B.; Yao, H.; Strome, R.; Lieberburg, I.; Rommens, J.; Kim. S.; Schenk, D.; Fraser, P.; St George Hyslop, P.; Selkoe, D. J. : Mutant presenilins of Alzheimer's disease increase production of 42-residue amyloid beta-protein in both transfected cells and transgenic mice. Nature Med. 3: 67-72, 1997. 3. De Strooper B, Saftig P, Craessaerts K, Vanderstichele H, Guhde G, Annaert W, Von Figura K, Van Leuven F. Deficiency of presenilin-1 inhibits the normal cleavage of amyloid precursor protein. Nature. Jan. 22, 1998 ;391 (6665):387-90 4. Goate, A.; Chartier-Harlin, M.-C.; Mullan, M.; Brown, J.; Crawford, F.; Fidani, L.; Giuffra, L.; Haynes, A.; Irving, N.; James, L.; Mant, R.; Newton, P.; Rooke, K.; Roques, P.; Talbot, C.; Pericak-Vance, M.; Roses, A.; Williamson, R.; Rossor, M.; Owen, M.; Hardy, J. : Segregation of a missense mutation in the amyloid precursor protein gene with familial Alzheimer's disease. Nature 349: 704-706, 1991 5. Levy-Lahad, E.; Wasco, W.; Poorkaj, P.; Romano, D. M.; Oshima, J.; Pettingell, W. H.; Yu, C.; Jondro, P. D.; Schmidt, S. D.; Wang, K.; Crowley, A. C.; Fu, Y.-H.; Guenette, S. Y.; Galas, D.; Nemens, E.; Wijsman, E. M.; Bird, T. D.;Schellenberg, G. D.; Tanzi, R. E. : Candidate gene for the chromosome 1 familial Alzheimer's disease locus. Science 269: 973-977, 1995. 6. Mehta N D, Refolo L M, Eckman C, Sanders S, Yager D, Perez-Tur J, Younkin S, Duff K, Hardy J, Hutton M. Increased Abeta42(43) from cell lines expressing presenilin 1 mutations. Ann.Neurol. 1998 Feb; 43(2):256-8. 7. Murayama O, Tomita T, Nihonmatsu N, Murayama M, Sun S, Honda T, Iwatsubo T, Takashima A. Enhancement of amyloid 42 secretion by 28 different presenilin 1 mutations of familial Alzheimer's. Neuroscience Letters 1999 April; 265 (1):61-63. 8. Mullan, M., Crawford, F., Axelman, K., Houlden, H., Lilius, L., Winblad, B., Lannfelt, L. A pathogenic mutation for probable Alzheimer's disease in the APP gene at the N-terminus of beta amyloid. Nat Genet. 1, 345-347 (1992). 9. Rogaev, E. I.; Sherrington, R.; Rogaeva, E. A.; Levesque, G.; Ikeda, M.; Liang, Y.; Chi, H.; Lin, C.; Holman, K.; Tsuda, T.; Mar, L.; Sorbi, S.; Nacmias, B.; Placentini, S.; Amaducci, L.; Chumakov, I.; Cohen, D.; Lannfelt, L.; Fraser, P. E.; Rommens, J. M.; St George-Hyslop, P. H. : Familial Alzheimer's disease in kindreds with missense mutations in a gene on chromosome 1 related to the Alzheimer's disease type 3 gene. Nature 376: 775-778, 1995. 10. Sherrington, R.; Rogaev, E. I.; Liang, Y.; Rogaeva, E. A.; Levesque, G.; Ikeda, M.; Chi, H.; Lin, C.; Li, G.; Holman, K.; Tsuda, T.; Mar, L.; Foncin, J.-F.; Bruni, A. C.; Montesi, M. P.; Sorbi, S.; Rainero, I.; Pinessi, L.; Nee, L.; Chumakov, I.; Pollen, D.; Brookes, A.; Sanseau, P.; Polinsky, R. J.; Wasco, W.; Da Silva, H. A. R.; Haines, J. L.; Pericak-Vance, M. A.; Tanzi, R. E.; Roses, A. D.; Fraser, P. E.; Rommens, J. M.; St George-Hyslop, P. H. : Cloning of a gene bearing mis-sense mutations in early-onset familial Alzheimer's disease. Nature 375: 754-760, 1995. 11. Suzuki, N., et al. An increased percentage of long amyloid beta protein secreted by amilial amyloid beta protein precursor (beta APP717) mutants. Science 264, 1336-1340 (1994). 12. Qian S, Jiang P, Guan X M, Singh G, Trumbauer M E, Yu H, Chen H Y, Van de Ploeg L H, Zheng H. Mutant human presenilin 1 protects presenilin 1 null mouse against embryonic lethality and elevates Abeta 1-42/43 expression. Neuron. 1998 Mar; 20(3):611-7. 13. Xia W, Zhang J, Kholodenko D, Citron M, Podlisny M B, Teplow D B, Haass D, Seubert P, Koo E H, Selkoe D J. Enhanced Production and Oligomerization of the 42-residue Amyloid-Protein by Chinese Hamster Ovary Cells Stably Expressing Mutant Presenilins J. Biol. Chem. 1997;272:7977-7982. 14. Zigmond, M. J, Bloom, F. E., Landis, S. C., Roberts, J. L., Squire, L. R.: Fundamental Neuroscience, Academic Press, 1999. 15. Li Y M, Xu M, Lai M T, Huang Q, Castro J L, DiMuzio-Mower J, Harrison T, Lellis C, Nadin A, Neduvelil J G, Register R B, Sardana M K, Shearman M S, Smith A L, Shi X P, Yin K C, Shafer J A, Gardell S J. Photoactivated gamma-secretase inhibitors directed to the active site covalently label presenilin 1. Nature. Jun. 8, 2000; 405(6787):689-94. 16. Rishton G M, Retz D M, Tempest P A, Novotny J, Kahn S, Treanor J J, Lile J D, Citron M. Fenchylamine sulfonamide inhibitors of amyloid beta peptide production by the gamma-secretase proteolytic pathway: potential small-molecule therapeutic agents for the treatment of Alzheimer's disease. J Med Chem. Jun. 15, 2000; 43(12):2297-9. 17. Tajima K, Babich S, Yoshida Y, Dantes A, Strauss J F 3rd, Amsterdam A. The proteasome inhibitor MG132 promotes accumulation of the steroidogenic acute regulatory protein (StAR) and steroidogenesis. FEBS Lett. Feb. 9, 2001; 490(1-2):59-64. 18. Marambaud P; Ancolio K; Lopez-Perez E; Checler F, Proteasome inhibitors prevent the degradation of familial Alzheimer's disease-linked presenilin 1 and potentiate A beta 42 recovery from human cells., Molecular Medicine 1998, v.4:147-157. 19. Gandy S; Naslund J; Nordstedt C, Alzheimer's disease Molecular consequences of presenilin-1 mutation, Nature Jun. 7, 2001; 411 (6838): 654-5. 20. Russo C; Schettini G; Saido T C; Hulette C; Lippa C; Lannfelt L; Ghetti B; Gambetti P; Tabaton M; Teller J K, reply: Alzheimer's disease Molecular consequences of presenilin-1 mutation, Nature Jun. 7, 2001; 411 (6838): 655 21. Russo C; Schettini G; Saido T C; Hulette C; Lippa C; Lannfelt L; Ghetti B; Gambetti P; Tabaton M; Teller J K, Presenilin-1 mutations in Alzheimer's disease., Nature Jun. 1, 2000; 405 (6786): 531-2 22. Glenner G G; Wong C W, Alzheimer's disease and Down's syndrome: sharing of a unique cerebrovascular amyloid fibril protein., Biochem Biophys Res Commun Aug. 16, 1984; 122 (3): 1131-5. BRIEF DESCRIPTION OF THE SEQUENCE LISTINGS SEQ ID NO:1 cDNA encoding mutant presenilin-1 (nucleotides 772-777 site directed mutagenesis sites directed by "n's) SEQ ID NO:2 cDNA encoding mutant presenilin-1 (nucleotides 1156-1161 site directed mutagenesis sites directed by "n's) SEQ ID NO:3 cDNA encoding mutant presenilin-1 (nucleotides 772-777 and 1156-1161 site directed mutagenesis sites directed by "n's) SEQ ID NO:4 mutant presenilin-1 (amino acids 258-259 variable amino acids denoted by "x"'s ) SEQ ID NO:5 mutant presenilin-1 (amino acids 386-387 variable amino acids denoted by "x"'s) SEQ ID NO:6 mutant presenilin-l (amino acids 258-259 and 386-387 variable amino acids denoted by "x"'s) SEQ ID NO:7 cDNA encoding mutant presenilin-2 (nucleotides 790-795 site directed mutagenesis sites directed by "n's) SEQ ID NO:8 cDNA encoding mutant presenilin-2 (nucleotides 1099-1104 site directed mutagenesis sites directed by "n's) SEQ ID NO:9 cDNA encoding mutant presenilin-2 (nucleotides 790-795 and 1099-1104 site directed mutagenesis sites directed by "n's) SEQ ID NO:10 mutant presenilin-2 (amino acids 264-265 variable amino acids denoted by "x"'s) SEQ ID NO:11 mutant presenilin-2 (amino acids 367-368 variable amino acids denoted by "x"'s) SEQ ID NO:12 mutant presenilin-2 (amino acids 264-265 and 367-368 variable amino acids denoted by "x"'s) SEQ ID NOS: 13-20 Mutagenesis oligonucleotides BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 Alignment of wild type and mutant presenilin-1 showing positions of site directed mutagenesis sites in bold type FIG. 2 Alignment of wild type and mutant presenilin-2 showing positions of site directed mutagenesis sites in bold type FIG. 3 512088 Drug Treatment and its Effect on A.beta..sub.1-40 levels in cell lines expressing APP.sub.SW KK alone, APP.sub.SW KK and Wild-Type PS1 and APP.sub.SW KK and PS1 wt/DTG FIG. 4 512088 Drug Treatment and its Effect on A.beta..sub.1-42 levels in cell lines expressing APP.sub.SW KK alone, APP.sub.SW KK and Wild-Type PS1 and APP.sub.SW KK and PS 1 wt/DTG FIG. 5 L685,458 Drug Treatment and its Effect on A.beta..sub.1-40 levels in cell lines expressing APP.sub.SW KK alone, APP.sub.SW KK and Wild-Type PS1 and APP.sub.SW KK and PS1 wt/DTG FIG. 6 L685,458 Drug Treatment and its Effect on A.beta..sub.1-42 levels in cell lines expressing APP.sub.SW KK alone, APP.sub.SW KK and Wild-Type PS1 and APP.sub.SW KK and PS1 wt/DTG FIG. 7 MG132 Drug Treatment and its Effect on A.beta..sub.1-40 levels in cell lines expressing APP.sub.SW KK alone, APP.sub.SW KK and Wild-Type PS1 and APP.sub.SW KK and PS1 wt/DTG FIG. 8 MG132 Drug Treatment and its Effect on A.beta..sub.1-42 levels in cell lines expressing APP.sub.SW KK alone, APP.sub.SW KK and Wild-Type PS1 and APP.sub.SW KK and PS1 wt/DTG FIG. 9 Vehicle (DMSO) Treatment and its Effect on A.beta..sub.1-40 levels in cell lines expressing APP.sub.SW KK alone, APP.sub.SW KK and Wild-Type PS1 and APPSWKK and PS1 wt/DTG FIG. 10 Vehicle (DMSO) Treatment and its Effect on A.beta..sub.1-42 levels in cell lines expressing APP.sub.SW KK alone, APP.sub.SW KK and Wild-Type PS1 and APP.sub.SW KK and PS1 wt/DTG SUMMARY OF THE INVENTION The present invention addresses the need identified above in that it provides heretofore unknown isolated mutant presenilin 1 and presenilin 2 (or herinafter "mutant PS1 and PS2) polypeptides and the isolated polynucleotide molecules that encode them, as well as vectors and host cells comprising such polynucleotide molecules. The invention provides an isolated polypeptide comprising at least 130 contiguous amino acids of SEQ ID NO:6 including amino acid residues 258 through 387 of SEQ ID NO:6 wherein residue 258 is selected from the group consisting of leucine, threonine or conservative substitutions of threonine, and/or wherein residue 259 is selected from the group consisting of valine, glycine or conservative substitutions of, and/or wherein residue 386 is selected from the group consisting of phenylalanine, threonine or conservative substitutions of threonine and/or wherein residue 387 is selected from the group consisting of isoleucine, glycine or conservative substitutions of glycine, with the proviso that a polypeptide where amino acid residue 258 is a leucine, amino acid residue 259 is a valine, amino acid residue 386 is a phenylalanine and amino residue 387 is a isoleucine is excluded The invention is intended to encompass each and every polypeptide represented by the above description. A preferred embodiment of the invention is a polypeptide which is at least 140, at least 150, at least 160, at least 170, at least 180, at least 190, at least 200, at least 210, at least 220, at least 230, at least 240, at least 250, at least 260, at least 270, at least 280, at least 300, at least 310, at least 320, at least 330, at least 340, at least 350, at least 360, at least 370, at least 380, at least 390, at least 400, at least 410, at least 420, at least 430, at least 440, at least 450, at least 460, at least 467 amino acids in length. A particularly preferred embodiment of the polypeptide of the invention comprises a polypeptide of 467 amino acids in length. The invention further provides, An isolated polypeptide comprising at least 110 contiguous amino acids of SEQ ID NO:12 including amino acid residues 264 through 368 of SEQ ID NO:6 wherein residue 264 is selected from the group consisting of leucine, threonine or conservative substitutions of threonine, and/or wherein residue 265 is selected from the group consisting of valine, glycine or conservative substitutions of glycine., and/or wherein residue 367 is selected from the group consisting of phenylalanine, threonine or conservative substitutions of threonine and/or wherein residue 368 is selected from the group consisting of isoleucine, glycine or conservative substitutions of glycine, with the proviso that a polypeptide where amino acid residue 258 is a leucine, amino acid residue 259 is a valine, amino acid residue 386 is a phenylalanine and amino residue 387 is a isoleucine is excluded The invention is intended to encompass each and every polypeptide represented by the above description. A preferred embodiment of the invention is a polypeptide which is at least 120, at least 130, at least 140, at least 150, at least 160, at least 170, at least 180, at least 190, at least 200, at least 210, at least 220, at least 230, at least 240, at least 250, at least 260, at least 270, at least 280, at least 300, at least 310, at least 320, at least 330, at least 340, at least 350, at least 360, at least 370, at least 380, at least 390, at least 400, at least 410, at least 420, at least 430, at least 440, at least 448 amino acids in length. A particularly preferred embodiment of the polypeptide above comprises a polypeptide of 448 amino acids in length. The invention further provides polynucleotides encoding the polypeptides of the invention. Each and every polynucleotide encoding the polypeptides of the invention are intended to be encompassed by the invention. In a related embodiment, the invention provides vectors comprising a polynucleotides of the invention. Such vectors are useful, e.g., for amplifying the polynucleotides in host cells to create useful quantities thereof. In other embodiments, the vector is an expression vector wherein the polynucleotide of the invention is operatively linked to a polynucleotide comprising an expression control sequence. Such vectors are useful for recombinant production of polypeptides of the invention. In another related embodiment, the invention provides host cells that are transformed or transfected (stably or transiently) with polynucleotides of the invention or vectors of the invention. As stated above, such host cells are useful for amplifying the polynucleotides and also for expressing the mutant PS1 and PS2 polypeptides or fragments thereof encoded by the polynucleotide. In still another related embodiment, the invention provides a method for producing a mutant PS1 or PS2 polypeptide (or fragment thereof) comprising the steps of growing a host cell of the invention in a nutrient medium and isolating the polypeptide from the cell or the medium. In still another related embodiment methods of identifying agents which modulate A.beta. derived peptide production. Such methods comprise contacting amyloid precursor protein (APP) and a mutant PS1 or PS2 polypeptide in the presence and absence of a test agent; determining the amount of at least one A.beta. derived peptide produced in the presence and absence of the test agent; and comparing the amount of at least one A.beta. derived peptide in the presence of the test agent to the amount of at least one A.beta. derived peptide in the absence of the test agent to identify an agent that modulates A.beta. derived peptide production wherein differing levels of said A.beta. derived peptide produced in the presence of a test agent identifies an agent that modulates A.beta. production In still another related embodiment, the invention provides a method for the identification of an agent capable of altering the ratio of A.beta..sub.1-40 /(A.beta..sub.1-40 +A.beta..sub.1-42)produced in any of the cell lines expressing mutant PS1 and PS2 polypeptides comprising the steps of: obtaining a test culture and a control culture of said cell line, contacting said test culture with a test agent, measuring the levels of A.beta..sub.1-40 and A.beta.1-42 produced by said test culture and said control culture, calculating the ratio of A.beta..sub.1-40 /(A.beta..sub.1-40 +A.beta..sub.1-42) for said test culture and said control culture from the levels of A.beta..sub.1-40 and A.beta..sub.1-42 measured, and comparing the ratio of A.beta..sub.1-40 /(A.beta..sub.1-40 +A.beta..sub.1-42) measured for said test culture and said control culture. A determination that the ratio of A.beta..sub.1-40 /(A.beta..sub.1-40 +A.beta..sub.42) for said test culture is higher or lower than ratio of A.beta..sub.1-40 /(A.beta..sub.1-40 +A.beta..sub.1-42) for said control culture indicates that said test agent has altered the ratio of A.beta..sub.1-40 /(A.beta..sub.1-40 +A.beta..sub.1-42). The invention further provides a transgenic non-human animal containing in germ or somatic cells, any of the nucleic acids described above. The encoded polypeptides can be used as a target for the screening of drugs useful in the treatment of useful in treating pathologies associated with aberrant APP processing including Alzheimer's disease. High-throughput assays for identifying inhibitors of presenilin activity are provided. High throughput assays are provided, as are related assay compositions, integrated systems for assay screening and other features that will be evident upon review. DETAILED DESCRIPTION OF THE INVENTION Definitions The term "wild-type" refers to a gene or gene product which has the characteristics of that gene or gene product when isolated from a naturally occurring source. A wild-type gene is that which is most frequently observed in a population and is thus arbitrarily designed the "normal" or "wild-type" form of the gene. In contrast, the term "modified" or "mutant" refers to a gene or gene product which displays modifications in sequence and or functional properties (i.e., altered characteristics) when compared to the wild-type gene or gene product. It is noted that naturally-occurring mutants can be isolated; these are identified by the fact that they have altered characteristics when compared to the wild-type gene or gene product. "Allelic variants" are modified forms of a wild type gene sequence, the modification resulting from recombination during chromosomal segregation or exposure to conditions which give rise to genetic mutation. Allelic variants, like wild type genes, are naturally occurring sequences (as opposed to non-naturally occurring variants which arise from in vitro manipulation). "Isolated" as used herein and as understood in the art, whether referring to "isolated" polynucleotides or polypeptides, is taken to mean that it is uniquely created by the inventors, separated from the original cellular or genetic environment in which the polypeptide or nucleic acid is normally found. As used herein therefore, by way of example only, a transgenic animal or a recombinant cell line constructed with a polynucleotide of the invention, incorporates the "isolated" nucleic acid. As used hereinafter "polynucleotide" generally refers to any polyribonucleotide or polydeoxribonucleotide, which may be unmodified RNA or DNA or modified RNA or DNA. "Polynucleotides" include, without limitation, single- and double-stranded DNA, DNA that is a mixture of single- and double-stranded regions, single- and double-stranded RNA, and RNA that is mixture of single- and double-stranded regions, hybrid molecules comprising DNA and RNA that may be single-stranded or, more typically, double-stranded or a mixture of single- and double-stranded regions. In addition, "polynucleotide" refers to triple-stranded regions comprising RNA or DNA or both RNA and DNA. The term "polynucleotide" also includes DNAs or RNAs containing one or more modified bases and DNAs or RNAs with backbones modified for stability or for other reasons. "Modified" bases include, for example, tritylated bases and unusual bases such as inosine. A variety of modifications may be made to DNA and RNA; thus, "polynucleotide" embraces chemically, enzymatically or metabolically modified forms of polynucleotides as typically found in nature, as well as the chemical forms of DNA and RNA characteristic of viruses and cells. "Polynucleotide" also embraces relatively short polynucleotides, often referred to as oligonucleotides. As used hereinafter "polypeptide" refers to any peptide or protein comprising two or more amino acids joined to each other by peptide bonds or modified peptide bonds, i.e., peptide isosteres. "Polypeptide" refers to both short chains, commonly referred to as peptides, oligopeptides or oligomers, and to longer chains, generally referred to as proteins. Polypeptides may contain amino acids other than the 20 gene-encoded amino acids. "Polypeptides" include amino acid sequences modified either by natural processes, such as post-translational processing, or by chemical modification techniques which are well known in the art. Such modifications are well described in basic texts and in more detailed monographs, as well as in a voluminous research literature. Modifications may occur anywhere in a polypeptide, including the peptide backbone, the amino acid side-chains and the amino or carboxyl termini. It will be appreciated that the same type of modification may be present to the same or varying degrees at several sites in a given polypeptide. Also, a given polypeptide may contain many types of modifications. Polypeptides may be branched as a result of ubiquitination, and they may be cyclic, with or without branching. Cyclic, branched and branched cyclic polypeptides may result from post-translation natural processes or may be made by synthetic methods. Modifications include acetylation, acylation, ADP-ribosylation, amidation, covalent attachment of flavin, covalent attachment of a heme moiety, covalent attachment of a nucleotide or nucleotide derivative, covalent attachment of a lipid or lipid derivative, covalent attachment of phosphotidylinositol, cross-linking, cyclization, disulfide bond formation, demethylation, formation of covalent cross-links, formation of cystine, formation of pyroglutamate, formylation, gamma-carboxylation, glycosylation, GPI anchor formation, hydroxylation, iodination, methylation, myristoylation, oxidation, proteolytic processing, phosphorylation prenylation, racemization, selenoylation, sulfation, transfer-RNA mediated addition of amino acids to proteins such as arginylation, and ubiquitination (see, for instance, Proteins-Structure and Molecular Properties, 2nd Ed., T. E. Creighton, W. H. Freeman and Company, New York, 1993; Wold, F., Post-translational Protein Modifications: Perspectives and Prospects, pgs. 1-12 in Postranslational Covalent Modification of Proteins, B. C. Johnson, Ed., Academic Press, New York, 1983; Seifter et al., "Analysis for protein modifications and nonprotein cofactors", Meth Enzymol (1990) 182:626-646 and Rattan et al., "Protein Synthesis: Post-translational Modifications and Aging", Ann NY Acad Sci (1992) 663:4842). As used herein, the term "test agent" means any identifiable chemical or molecule, including, but not limited to a small molecule, peptide, protein, sugar, nucleotide, or nucleic acid. Such a test agent can be natural or synthetic. As used herein, the term "contacting" means bringing together, either directly or indirectly, a compound into physical proximity to a polypeptide or polynucleotide of the invention. The polypeptide or polynucleotide can be present in any number of buffers, salts, solutions, etc. Contacting includes, for example, placing the compound into a beaker, microtiter plate, cell culture flask, or a microarray, such as a gene chip, or the like, which contains either the ion channel polypeptide or fragment thereof, or nucleic acid molecule encoding an ion channel or fragment thereof. The term "A.beta." (or .beta.-amyloid peptide) refers to a 38-43 amino acid peptide having a molecular weight of about 4.2 kD, which peptide is substantially homologous to the form of the protein described by Glenner et al., Biochem. Biophys. Res. Commun. 120, 885-890, (1984) including mutations and post translational modifications of the normal .beta.-amyloid peptide. In whatever form, the .beta.-amyloid peptide is an approximate 38-43 amino acid fragment of a large membrane-spanning glycoprotein, referred to as the .beta.-amyloid precursor protein (APP). .beta. amyloid peptide also includes sequences 1-6, SEQ ID NOs. 1-6 of U.S. Pat. No. 5,750,349, issued May 12, 1998 (incorporated into this document by reference). .beta. amyloid peptide is derived from a region of APP adjacent to and containing a portion of the transmembrane domain. Normally, processing of APP at the .alpha.-secretase site cleaves the midregion of the A.beta. sequence adjacent to the membrane and releases the soluble, extracellular domain of APP from the cell surface. This .alpha.-secretase APP processing creates "soluble APP.alpha."-, which is normal and not thought to contribute to AD. Pathological processing of APP at the .beta.- and .gamma.-secretase sites, which are located N-terminal and C-terminal to the .alpha.-secretase site, respectively, produces a very different result than processing at the .alpha. site. Sequential processing at the .beta.- and .gamma.-secretase sites releases the .beta. amyloid peptide" (.beta.) described above. The term "N terminally truncated A.beta." as used herein is defined as A.beta. in which N terminal amino acid residues are missing. "N terminal truncated A.beta." encompasses A.beta..sub.x-38, A.beta..sub.x-39, A.beta..sub.1-40, A.beta..sub.x-41, A.beta..sub.x-42, and A.beta..sub.x-43 wherein "x" is an integer greater than 1 and less than or equal to 22. Russo et al. Nature 405, 531-532 (2000); Russo et al. Nature 411, 655 (2001); Gandy et al. 411, 654-655 (2001). have characterized N terminal truncated A.beta. in the brains of patients suffering from sporadic or familial Alzheimer's disease due to mutations in PS1 or APP and found that N-terminally truncated A.beta. was overrepresented in Alzheimer's brains. Examples of N terminally truncated A.beta. include those described by Russo. The term "A.beta. derived peptides" as used herein is defined as encompassing A.beta. and N terminal truncated A.beta.. The term "A.beta.derived peptide" therefore encompasses A.beta..sub.x-38, A.beta..sub.x-39, A.beta..sub.x-40, A.beta..sub.x-41, A.beta..sub.x-42, and A.beta..sub.x-43 where "x" is defined as equal to 1 and less than or equal to 22. The term ".beta.-amyloid precursor protein" (APP) as used herein is defined as a polypeptide that is encoded by a gene of the same name localized in humans on the long arm of chromosome 21 and that includes A.beta. (see above), within its carboxyl third. APP is a glycosylated, single-membrane spanning protein expressed in a wide variety of cells in many mammalian tissues. Examples of specific isotypes of APP which are currently known to exist in humans are the 695 amino acid polypeptide described by Kang et. al. (1987) Nature 325:733-736 which is designated as the "normal" APP The 751 amino acid polypeptide described by Ponte et al. (1988) Nature 331:525-527 (1988) and Tanzi et al. (1988) Nature 331:528-530 and the 770-amino acid polypeptide described by Kitaguchi et. al. (1988) Nature 331:530-532. Examples of specific variants of APP include point mutations which can differ in both position and phenotype (for review of known variant mutation see Hardy (1992) Nature Genet. 1:233-234). In three APP mutants, valine-642 in the transmembrane domain of APP(695) is replaced by isoleucine, phenylalanine, or glycine in association with dominantly inherited familial Alzheimer disease. (According to an earlier numbering system, val642 was numbered 717 and the 3 mutations were V717I, V717F, and V717G, respectively.) Yamatsuji et al. ((1996) Science 272:1349-1352) concluded that these three mutations account for most, if not all, of the chromosome 21-linked Alzheimer disease. Suzuki et al. ((1994) Science 264:1336-1340) suggested that these mutations may cause Alzheimer disease by altering APP processing in a way that is amyloidogenic. They found that the APP-717 mutations were consistently associated with a 1.5- to 1.0-fold increase in the percentage of longer A.beta. generated and that the longer species formed insoluble amyloid fibrils more rapidly than did the shorter ones. In transgenic mice, overexpression of such mutants mimics the neuropathology of AD. The term "APP" encompasses fragments of APP other than those which consist solely of A.beta. or N terminally truncated A.beta.. The term "APP processing" refers to proteolytic cleavage of the APP molecule. APP processing is subject to intervention and may be "modified. The term "modulate A.beta. derived peptide production" means to change the amount of any A.beta. derived peptide produced. It will be appreciated that this definition also includes changing the relative proportion of individual species of A.beta. derived peptides one to another. By way of non limiting example therefore, a test agent which increases the ratio of A.beta..sub.1-40 /(A.beta..sub.1-40 +A.beta..sub.1-42) would be said to be an "agent which modulates A.beta. derived peptide production" as would an agent which reduces the levels of A.beta..sub.1-40 and A.beta..sub.1-42 each to the same extent would be "agent which modulates A.beta. derived peptide production". Polypeptides of the Invention Polypeptides of the present invention are mutants of the presenilin polypeptides (mutant PS1 polypeptide or mutant PS2 polypeptide). They are of interest because they are involved in the processing of amyloid precursor protein (APP) from which the major amylodogenic peptides A.beta..sub.1-40 or A.beta..sub.1-42 are cleaved. The cleavage of A.beta. from APP is accomplished by the action of two proteolytic activities commonly denoted as beta-secretase and gamma-secretase. The most common cause of familial Alzheimer's disease (FAD) are mutations found in the coding regions of the genes encoding presenilins 1 and 2 (hereinafter PS1 and PS2). The clinical mutations all cause at least one phenotypic alteration: increase in the production of A.beta..sub.1-42 from cells secreting the amyloid precursor protein (APP). Deletion of the PS1 gene in mice greatly reduces gamma-secretase activity. Recently it has been reported that the aspartic acid residues (D) found at positions 257 and 385 in PS1 and the homologous aspartic acid residues found at positions 263 and 366 in PS2 are necessary for gamma-secretase activity since changing these aspartic acid residues to either alanine or glutamic acid residues abrogates production of A.beta. in stably transfected cell lines carrying both mutated PS1 and PS2 (PS1m and PS2m) cDNAs. These observations suggest that there may be some intrinsic activity related to the transmembrane 6 and 7 aspartic acid residues which influences APP processing. The sequence following the D at amino acid position 257 in wild type PS1 is --LV (at amino acid positions 258 and 259). The sequence found after the D at amino position 385 in the wild type PS1 is --FI-- (at amino acid positions 386 and 387). The situation with PS2 is analogous. The sequence following the D at 263 in wild type PS2 is --LV (at amino acid positions 264 and 265). The sequence following the D at 366 in wild type PS2 is --FI (at amino acid positions 367 and 368). Without intending in any way to be bound by theory, it is postulated that the wild type sequences provide some minimal level of proteolytic activity with APP or gamma secretase as substrate to provide a phenotypic effect. The present invention optimizes the proteolytic activity so as to make possible an efficient assay for inhibitors of PS1 and PS2 activity. Single Partial and Single Complete Canonical Mutants of the Invention The present invention provides mutant PS1 polypeptides and nucleic acids encoding them which have a threonine and conservative substitutions of threonine at the position directly adjacent to either putative canonical aspartic residues and/or a glycine at the amino acid position one amino acid removed from either canonical aspartate. The present invention then, provides either "single partial canonical mutants" of PS1 (DLG, DTV, at 257-259 and DFG, DTI at 385-387) or "single complete canonical mutants" (DTG at positions 257-259 or 385-387). If conservative amino acid substitutions are introduced for T or G the mutants are designated "substituted single partial canonical mutants" or "substituted single complete canonical mutants" respectively. By way of example, a single mutant PS1, mutated at 258-259 to encode DLG would be designated `PS1-DLG/wt" and would be described as a "single partial canonical mutant". By way of further example a single mutant PS1 mutated at 258-259 to encode DTG at that positions would be designated PS1-DTG/wt and would be described as a "single complete canonical mutant" The present invention also provides mutant PS2 polypeptides and nucleic acids encoding them which have a threonine and conservative substitutions of threonine at the position directly adjacent to either putative canonical aspartic residues and/or a glycine at the amino acid position one amino acid removed from either canonical aspartate. The present invention then, provides either "single partial canonical mutants" of PS2 (DLG, DTV, at 263-265 and DFG, DTI at 366-368) or "single complete canonical mutants" (DTG at positions 263-265 or 366-368). If conservative amino acid substitutions are introduced for T or G the mutants are designated "substituted single partial canonical mutants" or "substituted single complete canonical mutants" respectively. By way of example, a single mutant PS2, mutated at 264-265 to encode DLG would be designated `PS1-DLG/wt" and would be described as a "single partial canonical mutant". By way of further example a single mutant PS2 mutated at 264-265 to encode DTG at that positions would be designated PS1-DTG/wt and would be described as a "single complete canonical mutant". Double Partial and Double Complete Canonical Site Mutants of the Invention The present invention provides mutant PS1 polypeptides and nucleic acids encoding them which have a threonine and conservative substitutions of threonine at the position directly adjacent to both putative canonical aspartic residues and/or a glycine at the amino acid position one amino acid removed from both canonical aspartate. The present invention then, provides either "double partial canonical mutants" of PS1 (DLG, DTV, at 257-259 and DFG, DTI at 385-387) or "double complete canonical mutants" (DTG at positions 257-259 or 385-387). If conservative amino acid substitutions are introduced for T or G the mutants are designated "substituted double partial canonical mutants" or "substituted double complete canonical mutants" respectively. By way of example, a double mutant PS1, mutated at 258-259 and 385-387 to encode DLG would be designated `PS 1-DLG/DLG" and would be described as a "double partial canonical mutant". By way of further example a double mutant PS1 mutated at 258-259 and 385-387 to encode DTG at both positions would be designated PS1-DTG/DTG and would be described as a "double complete canonical mutant" The present invention also provides mutant PS2 polypeptides and nucleic acids encoding them which have a threonine and conservative substitutions of threonine at the position directly adjacent to either putative canonical aspartic residues and/or a glycine at the amino acid position one amino acid removed from either canonical aspartate. The present invention then, provides either "double partial canonical mutants" of PS2 (DLG, DTV, at 263-265 and DFG, DTI at 366-368) or "double complete canonical mutants" (DTG at positions 263-265 or 366-368). If conservative amino acid substitutions are introduced for T or G the mutants are designated "substituted double partial canonical mutants" or "substituted double complete canonical mutants" respectively. By way of example, a double mutant PS2, mutated at 264-265 to encode DLG would be designated `PS1-DLG/wt" and would be described as a "single partial canonical mutant". By way of further example a single mutant PS2 mutated at 264-265 and 367-368 to encode DTG at both positions would be designated PS2-DTG/DTG and would be described as a "double complete canonical mutant". These --TG-and conservative variant substitutions in both PS1 and PS2 particularly the double mutants have a robust effect on A.beta..sub.1-42 but not A.beta..sub.1-40 production in the cell lines transfected. As such the polypeptides of the present invention would be useful to identify test agents which might inhibit their enhanced activity and thereby identify chemical structures which would be useful to inhibit the native activity of PS1 or PS2 in screens. The enhanced activity of the polypeptides of the present invention also provide a robust assay for candidate compound inhibitors of the native activity of the PS1 and PS2 polypeptides. The Polynucleotides of the Invention As is well known in the art, due to the degeneracy of the genetic code, there are numerous other DNA and RNA molecules that can code for the same polypeptide as that encoded by the aforementioned mutant PS1 and PS2 polypeptides. The present invention, therefore, contemplates those other DNA and RNA molecules which, on expression, encode the polypeptides of SEQ ID NOS: 4-6 and 10-12. Having identified the amino acid residue sequence encoded by a mutant PS1 or PS2 polypeptide, and with the knowledge of all triplet codons for each particular amino acid residue, it is possible to describe all such encoding RNA and DNA sequences. DNA and RNA molecules other than those specifically disclosed herein characterized simply by a change in a codon for a particular amino acid, are, therefore, within the scope of this invention. A table of amino acids and their representative abbreviations, symbols and codons is set forth below in the following Table 1. Amino acid Abbrev. Symbol Codon(s) Alanine Ala A GCA GCC GCG GCU Cysteine Cys C UGC UGU Aspartic acid Asp D GAC GAU Glutamic acid Glu E GAA GAG Phenylalanine Phe F UUC UUU Glycine Gly G GGA GGC GGG GGU Histidine His H CAC CAU Isoleucine Ile I AUA AUC AUU Lysine Lys K AAA AAG Leucine Leu L UUA UUG CUA CUC CUG CUU Methionine Met M AUG Asparagine Asn N AAC AAU Proline Pro P CCA CCC CCG CCU Glutamine Gln Q CAA CAG Arginine Arg R AGA AGG CGA CGC CGG CGU Serine Ser S AGC AGU UCA UCC UCG UCU Threonine Thr T ACA ACC ACG ACU Valine Val V GUA GUC GUG GUU Tryptophan Trp W UGG Tyrosine Tyr Y UAC UAU As is well known in the art, codons constitute triplet sequences of nucleotides in mRNA and their corresponding cDNA molecules Codons are characterized by the base uracil (U) when present in a mRNA molecule but are characterized by base thymidine (T) when present in DNA. A simple change in a codon for the same amino acid residue within a polynucleotide will not change the sequence or structure of the encoded polypeptide., It is apparent that when a phrase stating that a particular 3 nucleotide sequence "encode(s)" any particular amino acid, the ordinarily skilled artisan would recognize that the table above provides a means of identifying the particular nucleotides at issue. By way of example, if a particular three nucleotide sequence encodes theonine the table above discloses that the possible triplet sequences are ACA, ACG, ACC and ACU (ACT if in DNA). |
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