Global query on bacterial sirtuin CobB interactants reveals crosstalk with PRPP synthase Prs

In bacteria, post-translational acetylation of lysine residues affects the activities of numerous proteins, thus constituting an important regulatory mechanism that influences bacterial growth and adaptation to various environments. Conversely, the modification level of some lysine residues is controlled by deacetylases that remove the acetyl group. Most bacterial deacetylases are homologous to eukaryotic sirtuins, which utilize NAD+ as a cofactor. The Escherichia coli genome encodes a single sirtuin - CobB. However, both the regulation of CobB activity and the role that reversible acetylation plays in the control of protein functions and cellular pathways are not fully understood. In this study, we demonstrate that CobB forms a stable complex with PRPP synthase Prs. PRPP synthase is responsible for providing precursor metabolite for the synthesis of certain amino acids as well as nucleotides, including the cofactor NAD+. This association stimulates the deacetylation rate by CobB and protects it from inhibition by its reaction byproduct nicotinamide. We present evidence indicating that acetylation of Prs is physiologically significant and impacts E. coli metabolism and global protein acetylation level, although it does not affect CobB binding in vitro. In turn, Prs can be deacetylated by CobB, while formation of CobB-Prs complex formation safeguards PRPP synthase activity under non-optimal conditions. We propose that formation of the complex regulates deacetylation of other protein substrates by CobB.