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. 2021 Jun 15;10(6):1503. doi: 10.3390/cells10061503

Figure 4.

Figure 4

Post-translational modification of Rac1/Cdc42 and Rab-GTPases. The protein geranylgeranyl transferase-I (GGTase-I) transfers a geranylgeranyl group to proteins containing a C-terminal CAAX motif (where, C- cysteine, A- an aliphatic amino acid, and X- any amino acids). In contrast, Rab-GGTase does not recognize the CAAX motif, but requires an adaptor protein Rab escort protein (REP) to exert its function. REP recruits newly synthesized Rab-GTPases, and then presents them to the Rab-GGTase (GGTase-II). Once the geranylgeranyl group is inserted, as in the case of Rac1/Cdc42, the three terminal amino acids are removed by a Ras converting enzyme 1 (RCE-1). Furthermore, a methyl group is inserted onto the carboxylate anion of the prenylated cysteine via an ester linkage in the presence of S-adenosyl methionine by an enzyme protein-S-isoprenylcysteine O-methyltransferase (ICMT).