STRUCTURE AND MECHANISM OF PROTEIN PRENYLTRANSFERASES

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This proposal is concerned with the structure and mechanism of mammalian protein prenyltransferase proteins: farnesyltransferase (FTase) and geranylgeranyltransferase (GGTase-1). These proteins catalyze the addition of an isoprenoid lipid to a number of small regulatory G-proteins. This modification (prenylation) is essential for the activity and targeting of G-proteins to cell membranes. The FTase-mediated farnesylation of Ras oncogene proteins is absolutely required for their oncogenic, cell transforming activity. Treatment of Ras transformed cells with inhibitors of FTase has been shown to result in reversion of the transformed phenotype in tissue culture cells and animal models without apparent toxicity. Inhibition of Ras farnesylation is currently considered one of the most promising anti-cancer targets. Over 25 percent of human carcinomas are associated with oncogenic forms of Ras. Elucidation of the three-dimensional structure of FTase and its substrate complexes is therefore important both for understanding fundamental processes in signal transduction and for the development of pharmocologically active anti-cancer drugs or improved derivatives of existing drugs. GGTase-1 has also received attention recently as a potential target of the development of pharmaceuticals. The majority of prenylated proteins in the cell are modified by the geranylgeranyl isoprenoid. GGTase-1 catalyzes the prenylation of several members of the Ras superfamily involved in cell proliferation. Inhibition of GGTase-1 may be important not only for cancer chemotherapy, but also in the treatment of cardiovascular disease and the development of anti-fungal compounds. Furthermore, the structure of GGTase-1, particularly when compared to the structure of the related FTase, may further our understanding of the mechanisms of both peptide and isoprenoid substrate specificity. In addition, understanding the molecular basis for the differences between FTase and GGTase substrate specificities may facilitate the development of more selective FTase (and GGTase-1) inhibitors for anti-cancer therapy. The overall goal of this proposal is to study the molecular basis for the mechanism and substrate specificity of mammalian protein prenyltransferase proteins using X-ray crystallography to 1) determine the high resolution, three-dimensional structures of mammalian FTase substrate, product, and inhibitor complexes 2) determine the three-dimensional structure of mammalian GGTase-1 3) determine the structures of GGTase-1 together with substrates, products, and inhibitors.