Both farnesyltransferase (FT) and geranylgeranyltransferase 1 (GGT1) recognise a CaaX motif on their substrates where 'a' stands for preferably aliphatic residues, whereas GGT2 recognises a completely different motif. Important substrates for FT include, amongst others, many members of the Ras superfamily. GGT1 substrates include some of the other small GTPases and GGT2 substrates include the Rab family [2].

1: Crystal structure of farnesyl protein transferase complexed with a CaaX peptide and farnesyl diphosphate analogue. Strickland CL, Windsor WT, Syto R, Wang L, Bond R, Wu Z, Schwartz J, Le HV, Beese LS, Weber PC; Biochemistry 1998;37:16601-16611. PMID:9843427

2: Protein prenyltransferases. Maurer-Stroh S, Washietl S, Eisenhaber F; Genome Biol 2003;4:212. PMID:12702202

3: The crystal structures of phosphopantetheine adenylyltransferase with bound substrates reveal the enzyme's catalytic mechanism. Izard T; J Mol Biol. 2002;315:487-495. PMID:11812124

4: Structure of protein geranylgeranyltransferase-I from the human pathogen Candida albicans complexed with a lipid substrate. Hast MA, Beese LS; J Biol Chem. 2008;283:31933-31940. PMID:18713740