Date of Award
Doctor of Philosophy (PhD)
Microbiology and Immunology
Over billions of years, organisms have organized chemical reactions into metabolic pathways to sustain life. However, metabolic substrates can undergo many uncatalyzed, extra-metabolic reactions. Acetyl phosphate (AcP), an intermediate of the acetate fermentation pathway in E. coli, is one such metabolite that has been shown to non-enzymatically acetylate hundreds of proteins. This diverse set of targets suggests that acetylation could be a way for the cell to sense its nutritional status and regulate protein activity accordingly. However, how E. coli regulates acetylation, if at all, is unknown.Previous work showed that acetylation becomes pronounced in stationary phase cells. I determined that acetylation only increases once the culture enters stationary phase and continues to accumulate until carbon source depletion. Mass spectrometry indicated that the accumulation results from both additional lysine residues becoming acetylated and an increased ratio of acetylated to unacetylated isoforms. I performed anti-acetyllysine western blot analysis and metabolite measurements that suggested acetylation does not accumulate during exponential phase because 1) acetylated isoforms are diluted into nascent proteins and 2) glucose is not consumed until stationary phase. Additionally, I found that acetylation required rapid flux of carbon into the cell and through glycolysis. These data suggest that AcP-dependent acetylation is an unavoidable consequence of fermentation. I hypothesized that there is a physiological relevance to AcP-dependent acetylation such as utilization of acetylation as a carbon source or as protection against non-enzymatic protein damage, but I was unsuccessful in showing any effect.In addition to non-enzymatic acetylation, one lysine acetyltransferase (KAT), YfiQ, had been described in E. coli. I recognized that acetylation could occur without AcP or YfiQ. Indeed, I identified four proteins that produced acetylated bands in a strain lacking both mechanisms of acetylation. Variants of these proteins with conserved catalytic residues changed to alanine did not produce these acetylated bands, consistent with these proteins having KAT activity. One of these KATs, YiaC, inhibited migration in soft agar dependent on its KAT activity. To determine targets of these KATs, we determined proteins whose acetylation increased upon overexpresson of each of these proteins. Thus, this work opens new avenues of study to determine the regulatory potential of acetylation by these KATs.
Christensen, David George, "Regulation of Acetyl Phosphate-Dependent Acetylation and Identification of Novel Lysine Acetyltransferases in Escherichia Coli" (2019). Dissertations. 3328.
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Copyright © 2019 David George Christensen