Effects of prenyl modifications on interactions of small G proteins with regulators

This chapter discusses the effects of prenyl modifications on interactions of small G proteins with regulators. Small G proteins undergo posttranslational modifications with lipids. The small G proteins having a CaaX (C, cysteine; a, aliphatic amino acid; X, any amino acid) structure at the C-terminal region, such as Ras, are first farnesylated at the cysteine residue, followed by removal of the three amino acids and subsequent carboxylmethylation of the exposed cysteine residue. The functions of the posttranslational modifications for Ras are discussed in the chapter. The properties of three guanosine diphosphate/guanosine triphosphate (GDP/GTP) exchange proteins (GEPs), Rab GDP dissociation inhibitor (GDI), Rho GDI, and Smg GDP dissociation stimulator (GDS), and the methods for assessing the effects of lipid modifications of small G proteins on interactions with GDI and GDS are described. The Rab family members regulate the translocation and docking of the vesicle to the acceptor membrane. In this mechanism, the vesicle is translocated and docked to the acceptor membrane when GTP–Rab binds to the vesicle.