W0181

Structural Studies of Protein Farnesyltransferase with Bound Substrates. Stephen B. Long, Patrick J. Casey and Lorena S. Beese, Biochemistry, Duke University Medical Center, Durham, NC 27710 USA

Protein farnesyltransferase (FTase) catalyzes the covalent addition of a hydrophobic iosprenoid group from farnesyl diphosphate (FPP) to a cysteine residue near the C-terminus of protein substrate molecules such as Ras. Attachment of this lipid is essential for the subcellular localization to the plasma membrane and required for the transforming effect of mutant Ras molecules, making FTase a target molecule for the treatment of Ras-related cancers. FTase has high specificity for its protein and isoprenoid substrates, a property which has facilitated the design of potent and specific inhibitors of FTase. However, the molecular basis of substrate specificity is largely unknown.

The 2.25 Å resolution crystal structure of rat FTase (Park et al. and Beese, Science 275: 1800-1804, 1997) provided the first structural information on any protein prenyltransferase enzyme. Here we describe studies to obtain structural information on FTase with substrate molecules and inhibitors bound. We have determined the co-crystal structure of FTase with bound FPP. This complex reveals the location of isoprenoid substrate binding and allows us to propose a molecular ruler hypothesis for the basis of isoprenoid substrate specificity.