Membrane Localization of Ras Protein

The function of the Ras protein in cellular signal transduction is inseparably bound with the plasma membrane. The Ras proteins associate with the inner side of the cell membrane with the help of lipid anchors, such as famesyl residues and pahnitoyl residues (see 3.7). 

Famesylation of the Ras protein occurs at the C-terminal CAAX sequence (A aliphatic amino acid, X Ser or Thr). The famesyl residue is attached, with the help of a farnesyl protein transferase, via a thioether bond to the Cys residue of the CAAX sequence. Next, the last three amino acids are cleaved off by proteases and the carboxyl group of the C-terminal cysteine residue undergoes a methylesterification (Fig. 9.6). In addition, the Ras proteins have a palmitinic acid anchor at different Cys residues in the vicinity of the C terminus. The membrane localization of the Ki-Ras protein is also supported by a polybasic sequence close to the C terminus (see 3.7 and Fig. 3.12). 

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RAMI Beta subunit of the CAAX farnesyltransferase (FTase) that prenylates the a-factor mating pheromone and Ras proteins required for the membrane localization of Ras proteins and a-factor homolog of the mammalian FTase (3 subunit... 

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