Protein prenylation: a pivotal posttranslational process.

The joining of the 15-carbon farnesyl group ðC15H25Þ and the 20-carbon geranylgeranyl group ðC20H33Þ to protein–cysteines at or near their carboxy-termini is catalyzed by protein farnesyltransferase (FTase) and protein geranylgeranyltransferase-I and II (GGTase-I and GGTase-II) [1]. The prenyltransferases are heterodimers consisting of aand b-subunits with combined molecular masses ranging from 91 to 98 kDa. The asubunits of FTase and GGTase-I are the same, and the b-subunits differ. The b-subunits of the three enzymes are homologous to the a-subunits and to each other. The overall reactions are shown by the following chemical equations: FPPþHS-peptide ! farnesyl-S-peptideþ PP GGPP þHS-peptide ! geranylgeranyl-S-acceptor þ PP