Date of Award
Doctor of Philosophy (PhD)
James L. Hougland
Douglas A. Frank
Physical Sciences and Mathematics
Protein prenylation is a posttranslational modification involving the attachment of a C15 or C20 isoprenoid group to a cysteine residue near the C-terminus of the target substrate by protein farnesyltransferase (FTase) or protein geranylgeranyltransferase type I (GGTase-I), respectively. Both of these protein prenyltransferases recognize a C-terminal "CaaX" sequence in their protein substrates, but recent studies in yeast- and mammalian-based systems have demonstrated FTase can also accept sequences that diverge in length from the canonical four-amino acid motif, such as the recently reported five-amino acid C(x)3X motif. In this work, we further expand the substrate scope of FTase by demonstrating sequence-dependent farnesylation of shorter three-amino acid "Cxx" C-terminal sequences using both genetic and biochemical assays. Surprisingly, biochemical assays utilizing purified mammalian FTase and Cxx substrates reveal prenyl donor promiscuity leading to both farnesylation and geranylgeranylation of these sequences. The work herein expands the substrate pool of sequences that can be potentially prenylated, further refines our understanding of substrate recognition by FTase and GGTase-I and suggests the possibility of a new class of prenylated proteins within proteomes.
To identify potential new Cxx substrates in human proteomes, we explored a FRET-based system using phosphodiesterase delta subunit (PDE) as the acceptor protein for potentially prenylated Cxx sequences. While not conclusive, this work lays the foundation for an assay not dependent on membrane localization as a signal for prenylation inside cells and suggests future studies to improve upon the utility of this assay. Lastly, this work demonstrates FTase’s flexibility in accepting a prenyl donor analogue with an azobenzene moiety that can be modulated with light. This establishes a potential new avenue for mediating membrane localization behavior of prenylated proteins.
Ashok, Sudhat, "EXPANDING THE POTENTIAL PRENYLOME: PRENYLATION OF SHORTENED TARGET SUBSTRATES BY FTASE AND DEVELOPMENT OF FRET-BASED SYSTEM FOR DETECTING POTENTIALLY “SHUNTED” PROTEINS" (2020). Dissertations - ALL. 1185.