An insight into the role of the N-terminal domain of Salmonella CobB in oligomerization and Zn2+ mediated inhibition of the deacetylase activity.

Prokaryotic deacetylases are classified into nicotinamide adenine dinucleotide (NAD+)-dependent sirtuins and Zn2+-dependent deacetylases. NAD+ is a coenzyme for redox reactions, thus serving as an essential component for energy metabolism. The NAD+-dependent deacetylase domain is quite conserved and well characterized across bacterial species like CobB in Escherichia coli and Salmonella, Rv1151c in Mycobacterium, and SirtN in Bacillus subtilis. E. coli CobB is the only bacterial deacetylase with a known crystal structure (PDB ID: 1S5P), which has 91% sequence similarity with Salmonella CobB (SeCobB). Salmonella encodes two CobB isoforms, SeCobBS and SeCobBL, with a difference of 37 amino acids in its N-terminal domain (NTD). The hydrophobic nature of NTD leads to the stable oligomerization of SeCobBL. The homology modeling-based predicted structure of SeCobB showed the presence of a zinc-binding motif of unknown function. Tryptophan fluorescence quenching induced by ZnCl2 showed that Zn2+ has a weak interaction with SeCobBS but higher binding affinity toward SeCobBL, which clearly demonstrated the crucial role of NTD in Zn2+ binding. In the presence of Zn2+, both isoforms had significantly reduced thermal stability, and a greater effect was observed on SeCobBL. Dynamic light scattering (DLS) studies reflected a ninefold increase in the scattering intensity of SeCobBL upon ZnCl2 addition in contrast to an ∼onefold change in the case of SeCobBS, indicating that the Zn2+ interaction leads to the formation of large particles of SeCobBL. An in vitro lysine deacetylase assay showed that SeCobB deacetylated mammalian histones, which can be inhibited in the presence of 0.25-1.00 mM ZnCl2. Taken together, our data conclusively showed that Zn2+ strongly binds to SeCobBL through the NTD that drastically alters its stability, oligomeric status, and enzymatic activity in vitro.

Protein Acetyltransferases Mediate Bacterial Adaptation to a Diverse Environment.

Protein lysine acetylation is a conserved posttranslational modification that modulates several cellular processes. Protein acetylation and its physiological implications in eukaryotes are well understood; however, its role in bacteria is emerging. Lysine acetylation in bacteria is fine-tuned by the concerted action of lysine acetyltransferases (KATs), protein deacetylases (KDACs), and metabolic intermediates, e.g., acetyl coenzyme A (Ac-CoA) and acetyl phosphate (AcP). AcP-mediated nonenzymatic acetylation is predominant in bacteria due to its high acetyl transfer potential, whereas enzymatic acetylation by bacterial KATs (bKATs) is considered less abundant. SePat, the first bKAT discovered in Salmonella enterica, regulates the activity of the central metabolic enzyme acetyl-CoA synthetase, through its acetylation. Recent studies have highlighted the role of bKATs in stress responses like pH tolerance, nutrient stress, persister cell formation, antibiotic resistance, and pathogenesis. Bacterial genomes encode many putative bKATs of unknown biological function and significance. Detailed characterization of putative and partially characterized bKATs is important to decipher acetylation-mediated regulation in bacteria. Proper synthesis of information about the diverse roles of bKATs is missing to date, which can lead to the discovery of new antimicrobial targets in future. In this review, we provide an overview of the diverse physiological roles of known bKATs and their mode of regulation in different bacteria. We also highlight existing gaps in the literature and present questions that may help clarify the regulatory mechanisms mediated by bKATs in adaptation to a diverse habitat.