Determining the scope of prenylatable protein sequences

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PROJECT SUMMARY This study investigates the specificity of farnesyl transferase (FTase) that isoprenylates CaaX proteins. Studies probing the in vivo activity of the FTase have historically used reporters (e.g. Ras GTPases) that undergo complex multi-step post-translational modification (PTM), involving initial farnesylation followed by CaaX proteolysis and carboxyl methylation. This study takes advantage of Hsp40 Ydj1, a farnesylation-only reporter for which we have developed a range of methods to monitor its PTM status. Its use reveals that farnesylation is not necessarily coupled to subsequent PTMs as has been generally accepted for CaaX proteins, and that FTase specificity is significantly more promiscuous than anticipated. These findings challenge the conventional paradigm for how farnesylated proteins are modified and which proteins are targeted by FTase. We will extend our studies to fully resolve the specificity of FTase using a combination of genetic, biochemical, bioinformatic, and biophysical studies. We bring to bear on our investigations an exceptionally strong set of preliminary findings, the complementary expertise of several research groups, and a comprehensive molecular toolbox for the study of farnesylated proteins and other enzymes associated with this post-translational modification pathway.