Farnesyltransferase (EC 2.5.1.58) is one of the three enzymes in the prenyltransferase group. Farnesyltransferase (FTase) adds a 15-carbon isoprenoid called a farnesyl group to proteins bearing a CaaX motif: a four-amino acid sequence at the carboxyl terminus of a protein. Farnesyltransferase's targets include members of the Ras superfamily of small GTP-binding proteins critical to cell cycle progression. For this reason, several FTase inhibitors are undergoing testing as anti-cancer agents. FTase inhibitors have shown efficacy as anti-parasitic agents, as well. FTase is also believed to play an important role in development of progeria and various forms of cancers.

Farnesyltransferase catalyzes the chemical reaction

Thus, the two substrates of this enzyme are farnesyl diphosphate and protein-cysteine, whereas its two products are S-farnesyl protein and diphosphate.

Farnesyltransferase posttranslationally-modifies proteins by adding an isoprenoid lipid called a farnesyl group to the -SH of the cysteine near the end of target proteins to form a thioether linkage. This process, called farnesylation (which is a type of prenylation), causes farnesylated proteins to become membrane-associated due to the hydrophobic nature of the farnesyl group. Most farnesylated proteins are involved in cellular signaling wherein membrane association is critical for function.

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