Organic chemistry for structural biology: Probing the functional structure of proteins by photoaffinity labeling

Based on the recent development of recombinant techniques, the investigation of biofunctional machinery at their ligand accepting interfaces has become a challenging and important subject of organic chemistry in the oncoming new century. Three major approaches currently used for structural biology have their own advantages and limitations. Spectroscopic methods are useful for analyzing ligand-receptor interactions at the atomic level. These approaches, however,: usually require a significant amount of stable and pure proteins. Protein engineering based on gene technologies provides a series of mutants for the structural analysis of functional sites. One prerequisite for the use of this methods is that the mutants must, to a large extent, retain the conformation of the native receptors. Photoaffinity labeling, one of the third independent approach, has become increasingly appreciated as a powerful chemical methodology for the detailed structural analysis of ligand binding domains. The technique of photoaffinity labeling is a reliable chemical method which should be considered as being complementary to, rather than in competition with, the other two approaches. This review is focusing the recent application of photoaffinity labeling for probing the functional structure of ion channels, receptors, and enzymes.