MTN Activity Regulates Vitamin Dependent Metabolism

The microbial enzyme 5’-methylthioadenosine/S-adenosylhomocysteine (MTA/SAH) nucleosidase (MTN) has three substrates MTA, SAH and 5’-deoxyadenosine (5’dADO). In each case, MTN cleaves the glycosidic linkage between the adenine ring and ribose sugar. It is an essential part of methionine and purine salvage pathways, autoinducer-2 production, and radical S-adenosylmethionine (SAM) dependent reactions that are integral to vitamin synthesis. In this study, the impact of MTN activity on vitamin production and vitamin dependent metabolism were studied in E. coli strain O157:H7 wild type (WT) and MTN knock-out (KO) cells. Vitamins serve as cofactors for multiple pathways involved in bacterial metabolism. Proteomic studies comparing WT and KO strains have shown that the MTN KO strain expresses altered levels of enzymes responsible for reactions involved in vitamin synthesis (thiamine, lipoate, biotin, etc.) and downstream enzymes that depend on these vitamins for activity. The results of our studies suggest that loss of MTN activity leads to product inhibition of radical SAM reactions, thus altering global metabolism through decreases in activity of vitamin dependent enzyme steps. Since MTN is only present in microbes, not humans, and central to metabolism, it may be a good target for antibiotic development. Our studies are useful in demonstrating potential mechanisms of action for such antibiotics.