Acetylation of glucosyltransferases regulates Streptococcus mutans biofilm formation and virulence

Lysine acetylation is a frequently occurring post-translational modification (PTM), emerging as an important metabolic regulatory mechanism in prokaryotes. This process is achieved enzymatically by the protein acetyltransferase (KAT) to specifically transfer the acetyl group, or non-enzymatically by direct intermediates (acetyl phosphate or acetyl-CoA). Although lysine acetylation modification of glucosyltransferases (Gtfs), the important virulence factor in Streptococcus mutans, was reported in our previous study, the KAT has not been identified. Here, we believe that the KAT ActG can acetylate Gtfs in the enzymatic mechanism. By overexpressing 15 KATs in S. mutans, the synthesized water-insoluble extracellular polysaccharides (EPS) and biofilm biomass were measured, and KAT (actG) was identified. The in-frame deletion mutant of actG was constructed to validate the function of actG. The results showed that actG could negatively regulate the water-insoluble EPS synthesis and biofilm formation. We used mass spectrometry (MS) to identify GtfB and GtfC as the possible substrates of ActG. This was also demonstrated by in vitro acetylation assays, indicating that ActG could increase the acetylation levels of GtfB and GtfC enzymatically and decrease their activities. We further found that the expression level of actG in part explained the virulence differences in clinically isolated strains. Moreover, overexpression of actG in S. mutans attenuated its cariogenicity in the rat caries model. Taken together, our study demonstrated that the KAT ActG could induce the acetylation of GtfB and GtfC enzymatically in S. mutans, providing insights into the function of lysine acetylation in bacterial virulence and pathogenicity.

Possible Regulation of Toll-Like Receptor 4 By Lysine Acetylation Through LPCAT2 Activity in RAW264.7 Cells.

Inflammation is central to several diseases. TLR4 mediates inflammatory signals, however, there are gaps in the understanding of its mechanisms. Recently, TLR4 was found to co-localise with LPCAT2, a lysophospholipid acetyltransferase. This interaction influenced TLR4 subcellular localisation through an unknown mechanism. In this study, we have combined computational analysis, RNA interference technology, and biochemical analysis to investigate the possibility of TLR4 lysine acetylation and the influence of LPCAT2 on the detected lysine acetylation. The results suggest for the first time that TLR4 can undergo lysine acetylation and LPCAT2 can influence TLR4 lysine acetylation. This lays a foundation for further research on the role of lysine acetylation on TLR4 and the characterisation of LPCAT2 as a protein acetyltransferase.

Harnessing Ionic Selectivity In Acetyltransferase Chemoproteomic Probes

Chemical proteomics provides a powerful strategy for the high-throughput assignment of enzyme function or inhibitor selectivity. However, identifying optimized probes for an enzyme family member of interest and differentiating signal from background remain persistent challenges in the field. To address this obstacle, here we report a physiochemical discernment strategy for optimizing chemical proteomics based on the Coenzyme A (CoA) cofactor. First, we synthesize a pair of CoA-based Sepharose pulldown resins differentiated by a single negatively charged residue, and find this change alters their capture properties in gel-based profiling experiments. Next, we integrate these probes with quantitative proteomics and benchmark analysis of ‘probe selectivity’ versus traditional ‘competitive chemical proteomics’. This reveals the former is well-suited for the identification of optimized pulldown probes for specific enzyme family members, while the latter may have advantages in discovery applications. Finally, we apply our anionic CoA pulldown probe to evaluate the selectivity of a recently reported small molecule N-terminal acetyltransferase inhibitor. These studies further validate the use of physical discriminant strategies in chemoproteomic hit identification and demonstrate how CoA-based chemoproteomic probes can be used to evaluate the selectivity of small molecule protein acetyltransferase inhibitors, an emerging class of pre-clinical therapeutic agents.

N-terminal protein acetylation by NatB modulates the levels of Nmnats, the NAD+ biosynthetic enzymes in Saccharomyces cerevisiae

NAD+ is an essential metabolite participating in cellular biochemical processes and signaling. The regulation and interconnection among multiple NAD+ biosynthesis pathways are incompletely understood. Yeast (Saccharomyces cerevisiae) cells lacking the N-terminal (Nt) protein acetyltransferase complex NatB exhibit an approximate 50% reduction in NAD+ levels and aberrant metabolism of NAD+ precursors, changes that are associated with a decrease in nicotinamide mononucleotide adenylyltransferase (Nmnat) protein levels. Here, we show that this decrease in NAD+ and Nmnat protein levels is specifically due to the absence of Nt-acetylation of Nmnat (Nma1 and Nma2) proteins and not of other NatB substrates. Nt-acetylation critically regulates protein degradation by the N-end rule pathways, suggesting that the absence of Nt-acetylation may alter Nmnat protein stability. Interestingly, the rate of protein turnover (t½) of non-Nt-acetylated Nmnats did not significantly differ from those of Nt-acetylated Nmnats. Accordingly, deletion or depletion of the N-end rule pathway ubiquitin E3 ligases in NatB mutants did not restore NAD+ levels. Next, we examined whether the status of Nt-acetylation would affect the translation of Nmnats, finding that the absence of Nt-acetylation does not significantly alter the polysome formation rate on Nmnat mRNAs. However, we observed that NatB mutants have significantly reduced Nmnat protein maturation. Our findings indicate that the reduced Nmnat levels in NatB mutants are mainly due to inefficient protein maturation. Nmnat activities are essential for all NAD+ biosynthesis routes, and understanding the regulation of Nmnat protein homeostasis may improve our understanding of the molecular basis and regulation of NAD+ metabolism.

N-terminal protein acetylation by NatB modulates the levels of Nmnats, the NAD+ biosynthetic enzymes in Saccharomyces cerevisiae

ABSTRACTNAD+ is an essential metabolite participating in cellular biochemical processes and signaling. The regulation and interconnection among multiple NAD+ biosynthesis pathways are not completely understood. We previously identified the N-terminal (Nt) protein acetyltransferase complex NatB as a NAD+ homeostasis factor. Cells lacking NatB show an approximate 50% reduction in the NAD+ level and aberrant metabolism of NAD+ precursors, which are associated with a decrease of nicotinamide mononucleotide adenylyltransferases (Nmnat) protein levels. Here we show this decrease in NAD+ and Nmnat protein levels is specifically due to the absence of Nt-acetylation of Nmnat (Nma1 and Nma2) proteins, and not other NatB substrates. Nt-acetylation is a critical regulator of protein degradation by the N-end rule pathways, indicating absence of Nt-acetylation may alter Nmnat protein stability. Interestingly, the rate of protein turnover (t1/2) of non-Nt-acetylated Nmnats does not significantly differ from Nt-acetylated Nmnats, suggesting reduced Nmnat levels in NmatB mutants are not due to increased post-translational degradation of non-Nt-acetylated Nmnats. In line with these observations, deletion or depletion of N-rule pathway ubiquitin E3 ligases in NatB mutants is not sufficient to restore NAD+ levels. Moreover, the status of Nt-acetylation does not alter the rate of translation initiation of Nmnats. Collectively our studies suggest absence of Nt-acetylation may increase co-translational degradation of nascent Nmnat polypeptides, which results in reduced Nmnat levels in NatB mutants. Nmnat activities are essential for all routes of NAD+ biosynthesis. Understanding the regulation of Nmnat protein homeostasis will facilitate our understanding of the molecular basis and regulation of NAD+ metabolism.

YfmK is an Nε-lysine acetyltransferase that directly acetylates the histone-like protein HBsu in Bacillus subtilis

Nε-lysine acetylation is an abundant and dynamic regulatory posttranslational modification that remains poorly characterized in bacteria. In bacteria, hundreds of proteins are known to be acetylated, but the biological significance of the majority of these events remains unclear. Previously, we characterized the Bacillus subtilis acetylome and found that the essential histone-like protein HBsu contains seven previously unknown acetylation sites in vivo. Here, we investigate whether acetylation is a regulatory component of the function of HBsu in nucleoid compaction. Using mutations that mimic the acetylated and unacetylated forms of the protein, we show that the inability to acetylate key HBsu lysine residues results in a more compacted nucleoid. We further investigated the mechanism of HBsu acetylation. We screened deletions of the ∼50 putative GNAT domain-encoding genes in B. subtilis for their effects on DNA compaction, and identified five candidates that may encode acetyltransferases acting on HBsu. Genetic bypass experiments demonstrated that two of these, YfmK and YdgE, can acetylate Hbsu, and their potential sites of action on HBsu were identified. Additionally, purified YfmK was able to directly acetylate HBsu in vitro, suggesting that it is the second identified protein acetyltransferase in B. subtilis. We propose that at least one physiological function of the acetylation of HBsu at key lysine residues is to regulate nucleoid compaction, analogous to the role of histone acetylation in eukaryotes.

Regulation of a Protein Acetyltransferase in Myxococcus xanthus by the Coenzyme NADP+

ABSTRACTNADP+is a vital cofactor involved in a wide variety of activities, such as redox potential and cell death. Here, we show that NADP+negatively regulates an acetyltransferase fromMyxococcus xanthus, Mxan_3215 (MxKat), at physiologic concentrations.MxKat possesses an NAD(P)-binding domain fused to the Gcn5-typeN-acetyltransferase (GNAT) domain. We used isothermal titration calorimetry (ITC) and a coupled enzyme assay to show that NADP+bound toMxKat and that the binding had strong effects on enzyme activity. The Gly11 residue ofMxKat was confirmed to play an important role in NADP+binding using site-directed mutagenesis and circular dichroism spectrometry. In addition, using mass spectrometry, site-directed mutagenesis, and a coupling enzymatic assay, we demonstrated thatMxKat acetylates acetyl coenzyme A (acetyl-CoA) synthetase (Mxan_2570) at Lys622 in response to changes in NADP+concentration. Collectively, our results uncovered a mechanism of protein acetyltransferase regulation by the coenzyme NADP+at physiological concentrations, suggesting a novel signaling pathway for the regulation of cellular protein acetylation.IMPORTANCEMicroorganisms have developed various protein posttranslational modifications (PTMs), which enable cells to respond quickly to changes in the intracellular and extracellular milieus. This work provides the first biochemical characterization of a protein acetyltransferase (MxKat) that contains a fusion between a GNAT domain and NADP+-binding domain with Rossmann folds, and it demonstrates a novel signaling pathway for regulating cellular protein acetylation inM. xanthus. We found that NADP+specifically binds to the Rossmann fold ofMxKat and negatively regulates its acetyltransferase activity. This finding provides novel insight for connecting cellular metabolic status (NADP+metabolism) with levels of protein acetylation, and it extends our understanding of the regulatory mechanisms underlying PTMs.