Geranylgeranyltransferase types I (GGTase-I)-like proteins containing the protein prenyltransferase (PTase) domain, beta subunit (alpha 6 - alpha 6 barrel fold). GGTase-I s are a subgroup of the protein prenyltransferase family of lipid-modifying enzymes PTases catalyze the carboxyl-terminal lipidation of Ras, Rab, and several other cellular signal transduction proteins, facilitating membrane associations and specific protein-protein interactions. Prenyltransferases employ a Zn2+ ion to alkylate a thiol group catalyzing the formation of thioether linkages between cysteine residues at or near the C-terminus of protein acceptors and the C1 atom of isoprenoid lipids (geranylgeranyl (20-carbon) in the case of GGTase-I ). GGTase-I prenylates the cysteine in the terminal sequence, "CAAX" when X is Leu or Phe. Substrates for GTTase-I include the gamma subunit of neural G-proteins and several Ras-related G-proteins. PTases are heterodimeric with both alpha and beta subunits required for catalytic activity.
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