Molecular recognition of FTase and GGTase‐I in vivo

Abstract

Prenylation is an important post translational modification in which an isoprenyl tail is attached to the C‐terminus of a substrate protein, with protein farnesyltransferase (FTase) and protein geranylgeranyltransferase‐I (GGTase‐I) catalyzing the addition of a 15‐carbon farnesyl and 20‐carbon geranylgeranyl moiety, respectively. FTase and GGTase‐I have been proposed to recognize a canonical “CaaX” motif at the C‐terminus of protein substrates where “C” is cysteine, “a” is any aliphatic amino acid, and “X” is typically methionine, alanine, glutamate or serine for FTase and leucine or phenylalanine for GGTase‐I. However, recent studies indicate that the substrate selectivity of these enzymes may be more permissive with higher cross‐reactivity than originally proposed, raising the possibility that the cellular pool of prenylated proteins includes a wide range of C‐terminal sequences. In the human genome, ~700 proteins contain a cysteine four amino acids from the C‐terminus, but only ~70 proteins have been demonstrated to be farnesylated in vivo. To examine prenylation motifs in vivo, we created a library of GFP‐CaaX fusion proteins and are measuring the prenylation status using mass spectrometry and protein localization using fluorescence microscopy. These studies will provide insight into the in vivo specificity of prenyltransferases and the involvement of prenylation in various cellular processes.