| METHOD | Few good methods exist for selective detection of metal ions. Yet microorganisms detect metal ions selectively with the help of the MerR protein family. Chuan He, an assistant professor of chemistry at the University of Chicago, and graduate student Peng Chen used the MerR specificity to design a strategy for creating selective, fluorescent metal ion biosensors [J. Am. Chem. Soc., 126, 728 (2004)]. MerR proteins bind to specific sequences of double-stranded DNA. When a specific metal ion then binds to the protein, the protein untwists the DNA helix and breaks apart two base pairs in the middle of the duplex. If a fluorescent cytosine analog, pyrrolo-C, is incorporated into just the right spot on the DNA strand, it fluoresces after being unpaired. Chen and He built two examples of what they think can be a sensor using any MerR protein. They used E. coli's MerR, which binds primarily to Hg2+, and CueR, which responds to Cu+, Ag+, or Au+. Addition of the metal ion typically caused a threefold increase in fluorescence in seconds. In addition to metal sensing, He believes that the sensors can be used to probe the behavior of newly discovered MerR proteins |
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