Methionine Salvage Pathway is Promiscuous Towards 5′-Deoxyadenosine and 5′-Methylthioadenosine

Abstract

S-Adenosylmethionine (aka. SAM or AdoMet) is a highly reactive metabolite that can be useful by many organisms for a variety array of biosynthesis and regulatory purposes. Common enzymes and biosynthetic pathways that require SAM include certain methyltransferase enzymes, polyamine biosynthetic pathways and the radical SAM enzyme superfamily. Overall, from these common biological pathways, as SAM is consumed to perform several unique functions, S-adenosylhomocysteine (SAH), 5’-methylthioadenosine (MTA), and 5’-deoxyadenosine (5’-dAH) are produced as byproducts. There are known pathways to recycle or degrade SAH and MTA. However, for 5’-dAH, no recycling or degradation pathway has yet been discovered. Recent works by the Jarrett laboratory has found that certain enzymes in Escherichia coli have sequence homology to characterized enzymes from the eukaryotic methionine salvage pathway that normally recycle MTA to form methionine. Our findings suggest that these E. coli methionine salvage pathway enzymes can likely also degrade 5’-dAH, suggesting that the methionine salvage pathway is highly promiscuous towards degrading MTA, 5’-dAH, and possibly even SAH. So far, research on the methionine salvage pathway (including the Jarrett laboratory) has shown that the first pathway enzyme: 5’-methylthioadenosine nucleosidase (MtnN) is promiscuous and cleaves adenine from MTA, 5’-dAH, and SAH to produce 5-methylthioribose (MTR), 5-deoxyribose, and S-ribosylhomocysteine (SRH) respectively. To expand upon the theme of enzyme promiscuity, I turned my attention to the second methionine salvage pathway enzyme in E. coli: 5-methylthioribose kinase (MtnK). This dissertation will discuss investigations of E. coli MtnK and the reaction catalyzed by this enzyme with MTR, 5-deoxyribose, and SRH substrates.