W0386

Protein prenyltransferases are a ubiquitous and essential family of eukaryotic enzymes that catalyze the attachment of a lipid group to heterotrimeric and small GTPase proteins (G proteins). This lipid modification, called protein prenylation, allows association with the cell membrane, promotes protein-protein interactions with other signal transduction members, and is required for the transforming activity of oncogenic mutants. The CaaX prenyltransferase family, so called because they recognize protein substrates with a C-terminal CaaX sequence, has two members: protein geranylgeranyltransferase type-I (GGTase-I), which catalyzes the addition of a 20-carbon lipid to substrate proteins, and protein farnesyltransferase (FTase), which catalyzes the addition of a 15-carbon lipid to substrate proteins. CaaX prenyltransferase inhibitors are currently in clinical trials for the treatment in cancer, and are being tested for the treatment of inflammation, heart disease, and parasitic organisms. We have determined a series of crystal structures representing major steps along the FTase (Long et al., Nature 2002) and GGTase-I reaction coordinate. These structures illustrate the unique biochemical properties of each enzyme, and suggest a common reaction mechanism shared by all protein prenyltransferases. Also, these structures reveal a heretofore unrecognized motif conserved on all protein prenyltransferases that suggests an additional role in the cell. Here we present FTase and GGTase-I structures complexed with different protein and lipid substrates. Using these structures, and previous biochemical findings, we propose a molecular model for CaaX prenyltransferase specificity. Finally, we have determined structures of GGTase-I and FTase complexed with different inhibitors. These structures give insight into inhibitor specificity mechanisms, and should help in lead compound optimization and the further development of novel inhibitors.