CAAX protein prenylation characteristics

Prenylated proteins have characteristic C-terminal sequences. For example, the three allelic Ras proteins (H-Ras, K-Ras, and N-Ras) expressed in mammalian tissues contain a C-terminal tetrapeptide which begins with cysteine, and ends with either methionine or serine. This part of the molecule is referred to as the CaaX box where C = cysteine, a = an aliphatic amino acid, and X = a prenylation specificity residue. The first step in the posttranslational processing of Ras proteins utilizes FTase and farnesyl diphosphate (FPP) to covalently attach a farnesyl group to the cysteine thiol of the CaaX box. While subsequent processing events involve proteolytic removal of the aaX tripeptide and methylation of the resulting C-termi-nal carboxylate group, only the farnesyl modification is required for mutant Ras proteins to associate with the cell membrane and transform a cell.2-6... 

The y-subunit contains a characteristic CAAX motif, which allows covalent attachment of prenyl groups and anchors the protein to the inner surface of the membrane. 

Protein substrates that undergo prenylation have a unique identifying signature sequence at the carboxyl end that consists of a cysteine, two aliphatic amino acids and any amino acid to form the characteristic CaaX box. Proteins having this characteristic signature include the nuclear lamins and members of the Ras family (Ras, l o, and Rab) as well as several other proteins [25,30-32]. 

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