Geranylgeranyltransferase type II (GGTase-II)_like proteins containing the protein prenyltransferase (PTase) domain, beta subunit (alpha 6 - alpha 6 barrel fold). GGTase-IIs 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-II ). GGTase-II catalyzes alkylation of both cysteine residues in Rab proteins containing carboxy-terminal "CC", "CXCX" or "CXC" motifs. PTases are heterodimeric with both alpha and beta subunits required for catalytic activity. In contrast to other prenyltransferases, GGTas-II requires an escort protein to bring the substrate protein to the catalytic heterodimer and to escort the geryanylgeranylated product to the membrane.
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