Geranylgeranyltransferase type I GGTase

The first step of the series of modifications involved in the processing of CAAX-type prenyl proteins occurs in the cytoplasm, catalyzed by either protein farnesyltransferase (FTase) or protein geranylgeranyltransferase type I (GGTase-I). The specificity for either of these two enzymes for the most part depends on the identity of the last amino acid X of the CAAX consensus sequence. When X is serine, cysteine, alanine, or glutamine, the 15 carbon farnesyl group is added to the cysteine catalyzed by FTase and when X is leucine, the 20 carbon geranylgeranyl group is added by... 

Khan, O.M., et al. (2011). Geranylgeranyltransferase type I (GGTase-I) deficiency hyper-activates macrophages and induces erosive arthritis in mice. J Clin Invest 121 628-639. 

S, Q, A, or C, whereas GGTase-I recognizes CaaX boxes with X = L or F. Other prenylated proteins, such as the Rab proteins involved in vesicular transport, terminate in a CC, CXC, or CC(X) , 3 motif these proteins are substrates for protein geranylgeranyltransferase type II (GGTase-II) [3]. In order to be prenylated, Rab proteins must associate with Rab escort protein after geranylgeranylation, Rab escort protein delivers the prenylated Rab to membranes. 

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