Our laboratory studies prokaryotic metabolism and physiology. We are currently analyzing the role of reversible lysine acetylation (RLA), the biosynthesis of coenzyme B12, and strategies used by prokaryotes to avoid metabolic stress caused by reactive metabolic intermediates. RLA is an epigenetic regulatory mechanism for the control of protein function. We first described the role of RLA in prokaryotic metabolism over a decade ago in Salmonella. We have expanded our studies to firmicutes, α-proteobacteria and actinomycetes in an effort to understand the rules governing this process. We have studied the complex pathway of coenzyme B12 biosynthesis in bacteria and archaea for over two decades. We have discovered new enzymes, pathways and strategies to assemble the largest coenzyme known. Lastly, we are interested in the molecular mechanisms underpinning the toxicity of short-chain fatty acids such as acetate and propionate, as well as other aspects of C2 metabolism.
For over three decades, we have investigated multiple aspects of the biosynthesis of adenosylcobalamin (AdoCbl, coenzyme B12) in bacteria and archaea. We have discovered new enzymes and pathways in archaea and bacteria for the assimilation of incomplete corrinoids and other precursors from the environment.
We discovered a strategy for the synthesis of specific structural variants of the coenzyme that may allow organisms to outcompete others in their environment. It is remarkable that even though the biosynthesis of coenzyme B12 has been studied for decades, we still have an incomplete picture of how the assembly of this complex molecule is achieved, and have almost no information of why this major biosynthetic pathway is intimately associated with the cell membrane in all organisms known to make it. We have made numerous contributions to our understanding of the biochemistry and genetics of AdoCbl biosynthesis, but the goal is to provide a physiological framework for this major biosynthetic pathway.
Acylation of the epsilon amino group of the side chain of lysine is a post-translational modification that has been extensively studied in eukaryotes, but only to a limited extent in bacteria and archaea. Our goal is to understand the physiological roles of lysine acylation in prokaryotic systems. Bioinformatics analyses suggest that prokaryotic modifying/de-modifying systems are diverse, and in some microorganisms the number or putative modifying enzymes is large.
Fundamental information about these systems is lacking. For example, the substrates for most of these putative enzymes are not known. In fact, we do not know whether the substrates are small molecules, nucleic acids, proteins, etc. The effects of the absence or overproduction of these systems is also unclear. Our lab has made seminal contributions to the field, and is actively pursuing several projects in this area of research.
This area of our work centers on the catabolism of acetate and propionate, two short-chain fatty acids that are abundant in soil and the gut, but whose catabolism generates potent inhibitors. Our work led to the discovery of the 2-methylcitric acid cycle as the predominant pathway of propionate catabolism in bacteria.
We are investigating the molecular basis of acetate and propionate toxicity, and the mechanisms used by the cell to avoid the toxic effects of these compounds. We showed that cells that cannot catabolize 2-methylcitrate are glucose auxotrophs, and that such auxotrophy is due to inhibitory effects of 2-methylcitrate on fructose biphosphatase, a key gluconeogenic enzyme. Our goals is to continue to identify other functions affected by 2-methylcitrate.
Parks, AR, McCormick, RD, Byrne, JA, Escalante-Semerena, JC.
The coenzyme B12 precursor 5,6-dimethylbenzimidazole is a flavin antagonist in Salmonella
Malalasekara, LR, and Escalante-Semerena, JC.
Jeter, VL, AH Schwarzwalder, I Rayment, I, and JC Escalante-Semerena..
Location
University of Georgia
Department of Microbiology
527 Biological Sciences Building
120 Cedar Street
Athens, GA 30602
Phone & Email
Office Ph: 706-542-2651
Lab Ph: 706-542-0512
Lab Ph: 706-542-9275
Fax: 706-542-2815
[email protected]