Solid-Phase Synthesis Of Prenylated Peptides Containing C-Terminal Esters: A Chemical Biology Tool For The Study Of Protein Prenylation

Abstract

Protein prenylation is a post-translational modification that comprises the attachment of either a farnesyl or a geranylgeranyl isoprenoid. This covalent, irreversible modification has been studied extensively due to its importance for the proper cellular activity of numerous proteins. Due to appearance of mutated forms of farnesylated Ras in around 30% of all human cancers, substantial efforts have been focused on the development of FTase inhibitors (FTI). Despite numerous studies on the enzymology of the proteins involved in this pathway many questions remains about the protein prenylation process in cells. The mating pheromone a-factor is a farnesylated dodecapeptide found in the budding yeast S. cerevisiae which biosynthesis encompasses the same processing pathway than Ras proteins (farnesylation of C-terminal cysteine, C-terminal proteolysis and C-terminal methyl esterification). For mating, a-factor travels to the cell surface of the opposite mating cell were it binds and activate a membrane receptor. In this dissertation, our efforts in using a-factor as a model system to understand the role of prenyl groups in protein-protein interactions is described. First, we developed a method for the solid-phase synthesis of peptides containing the C-terminal cysteine esters found in mature prenylated proteins. Next, we have shown that not only methyl esters but also peptides containing ethyl, isopropyl and benzyl cysteine esters may be obtained with our strategy. Additionally, the approach was used to prepare a-factor and a-factor analogs that were tested for their biological activities. Our results indicate that this simple method can be used for the synthesis of a variety of C-terminal ester modified peptides that should be useful in studies of protein prenylation and other structurally related biological processes.