STRUCTURE-BASED ANALYSIS OF CATALYSIS AND SUBSTRATE DEFINITION IN THEHIT PROTEIN FAMILY

The histidine triad (HIT) protein family is among the most ubiquitous and highly conserved in nature, but a biological activity has not yet been identified for any member of the HIT family. Fragile histidine tr iad protein (FHIT) and protein kinase C interacting protein (PKCI) wer e used in a structure-based approach to elucidate characteristics of i n vivo ligands and reactions. Crystallographic structures of ape, subs trate analog, pentacovalent transition-state analog, and product slate s of both enzymes reveal a catalytic mechanism and define substrate ch aracteristics required for catalysis, thus unifying the HIT family as nucleotidyl hydrolases, transferases, or both. The approach described here may be useful in identifying structure-function relations between protein families identified through genomics.