| COMMENTS |
By using a stable analog of cytidine-5'-monophospho-N-acetylneuraminic acid (the enzyme's substrate), Strynadka and coworkers were able to hypothesize a plausible mechanism of action for sialyl transfer. "A histidine acts as a base to assist nucleophilic attack of the acceptor hydroxyl, and a tyrosine is used as an acid to assist the departure of cytidine-5'-monophosphate," explains Chi-Huey Wong of Scripps Research Institute. "Further understanding of the specificity and detailed mechanism of the reaction should provide valuable information for design of new substrates and inhibitors," Wong says. James C. Paulson, also of Scripps, says the study is an important breakthrough, but he notes the bacterial enzyme has "minimal homology to mammalian enzymes, where most of the interest is." Davies agrees that "it remains to be seen how relevant this structure is to higher organism sialylation, since the Campylobacter enzyme is not closely related, at least at the sequence level, to human sialyltransferases." But Monica M. Palcic of the University of Alberta, Edmonton, says she "would expect mammalian sialyltransferases to exhibit similar topography." |
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