4.1.2. Carbon source-regulated protein acetylation
Comparative studies with different carbon sources have explored the effect of protein acetylation during growth under glycolytic and oxidative conditions. As Wang and collaborators demonstrated, S. enterica presents changes in cell growth and significant difference in the percentage of acetylated proteins in response to glucose or citrate. A total of 15 enzymes were identified with altered acetylation status in response to a carbon source, and all of them showed higher acetylation levels in cells grown in glucose (Wang et al., 2010). The main targets of lysine acetylation were enzymes involved in central metabolism, and a correlation was observed in the cell growth and the acetylation levels on these proteins; in a medium containing glucose, cells grow faster, and an increase in the acetylation of central metabolic enzymes was observed, but when the acetylation decreases, opposite growth properties were observed (Wang et al., 2010). In Bacillus subtilis , different acetylation levels have also been reported in different carbon sources. in decreasing order, protein acetylation occurs in a medium containing only carbon source pyruvate, glucose, glycerol, or citrate. (Kosono et al., 2015). The main differences in the acyl modification patterns were observed in glucose and citrate. In fact, it was under these two conditions that changes in the acetylation sites were determined. Acetylation was upregulated at 13 sites in the glucose condition relative to the citrate condition, and as in S. enterica , acetylation positively modulated the growth of this bacterium in glucose-medium (Kosono et al., 2015). Western immunoblot analysis found that glucose and lactate produce global acetylation in E. coli K-12, which increased after the cells had entered the stationary phase. Induction of acetylation at this growth point requires continue exposure to carbon sources, specifically glucose (Schilling et al., 2015). The results suggest that the protein acetylation may have a physiological role in mediating adaptation to different carbon sources.
Another factor that could determine the lysine acetylation levels is the sugar amount. In E. coli, there is no difference in acetylation patterns during growth in glucose or xylose as the sole carbon source. However, an increase in the relative abundance of acetylation at high concentrations of these two carbohydrates has been observed, indicating that acetylation only sometimes has a regulatory role in obtaining specific carbon sources (Schilling et al., 2019). Also, acetylation increases in parallel with glucose consumption and acetate excretion (Schilling et al., 2015; Schilling et al., 2019). The results support the hypothesis that protein acetylation regulates metabolism in response to energy status, mainly when the carbon flux exceeds the capacity of the tricarboxylic acid (TCA) cycle, resulting in overflow metabolism (Schilling et al., 2015; Schilling et al., 2019).