Rv0802c is an acyltransferase that succinylates and acetylates Mycobacterium tuberculosis nucleoid-associated protein HU

Nucleoid-associated proteins of mycobacteria come with a distinctive flavor

In every bacterium, nucleoid-associated proteins (NAPs) play crucial roles in chromosome organization, replication, repair, gene expression, and other DNA transactions. Their central role in controlling the chromatin dynamics and transcription has been well-appreciated in several well-studied organisms. Here, we review the diversity, distribution, structure, and function of NAPs from the genus Mycobacterium. We highlight the progress made in our understanding of the effects of these proteins on various processes and in responding to environmental stimuli and stress of mycobacteria in their free-living as well as during distinctive intracellular lifestyles. We project them as potential drug targets and discuss future studies to bridge the information gap with NAPs from well-studied systems.

Identification of a 1-acyl-glycerol-3-phosphate acyltransferase from Mycobacterium tuberculosis, a key enzyme involved in triacylglycerol biosynthesis

Latent tuberculosis, caused by dormant Mycobacterium tuberculosis (Mtb), poses a threat to global health through the incubation of undiagnosed infections within the community. Dormant Mtb, which is phenotypically tolerant to antibiotics, accumulates triacylglycerol (TAG) utilizing fatty acids obtained from macrophage lipid droplets. TAG is vital to mycobacteria, serving as a cell envelope component and energy reservoir during latency. TAG synthesis occurs by sequential acylation of glycerol-3-phosphate, wherein the second acylation step is catalyzed by acylglycerol-3-phosphate acyltransferase (AGPAT), resulting in the production of phosphatidic acid (PA), a precursor for the synthesis of TAG and various phospholipids. Here, we have characterized a putative acyltransferase of Mtb encoded by Rv3816c. We found that Rv3816c has all four characteristic motifs of AGPAT, exists as a membrane-bound enzyme, and functions as 1-acylglycerol-3-phosphate acyltransferase. The enzyme could transfer the acyl group to acylglycerol-3-phosphate (LPA) from monounsaturated fatty acyl-coenzyme A of chain length 16 or 18 to produce PA. Complementation of Escherichia coli PlsC mutant in vivo by Rv3816c confirmed that it functions as AGPAT. Its active site mutants, H43A and D48A, were incapable of transferring the acyl group to LPA in vitro and were not able to rescue the growth defect of E. coli PlsC mutant in vivo. Identifying Rv3816c as AGPAT and comparing its properties with other AGPAT homologs is not only a step toward understanding the TAG biosynthesis in mycobacteria but has the potential to explore it as a drug target.

The Mycobacterium tuberculosis methyltransferase Rv2067c manipulates host epigenetic programming to promote its own survival

Mycobacterium tuberculosis has evolved several mechanisms to counter host defense arsenals for its proliferation. Here we report that M. tuberculosis employs a multi-pronged approach to modify host epigenetic machinery for its survival. It secretes methyltransferase (MTase) Rv2067c into macrophages, trimethylating histone H3K79 in a non-nucleosomal context. Rv2067c downregulates host MTase DOT1L, decreasing DOT1L-mediated nucleosomally added H3K79me3 mark on pro-inflammatory response genes. Consequent inhibition of caspase-8-dependent apoptosis and enhancement of RIPK3-mediated necrosis results in increased pathogenesis. In parallel, Rv2067c enhances the expression of SESTRIN3, NLRC3, and TMTC1, enabling the pathogen to overcome host inflammatory and oxidative responses. We provide the structural basis for differential methylation of H3K79 by Rv2067c and DOT1L. The structures of Rv2067c and DOT1L explain how their action on H3K79 is spatially and temporally separated, enabling Rv2067c to effectively intercept the host epigenetic circuit and downstream signaling.

The role of Mycobacterium tuberculosis acetyltransferase and protein acetylation modifications in tuberculosis

Tuberculosis (TB) is a widespread infectious disease caused by Mycobacterium tuberculosis (M. tb), which has been a significant burden for a long time. Post-translational modifications (PTMs) are essential for protein function in both eukaryotic and prokaryotic cells. This review focuses on the contribution of protein acetylation to the function of M. tb and its infected macrophages. The acetylation of M. tb proteins plays a critical role in virulence, drug resistance, regulation of metabolism, and host anti-TB immune response. Similarly, the PTMs of host proteins induced by M. tb are crucial for the development, treatment, and prevention of diseases. Host protein acetylation induced by M. tb is significant in regulating host immunity against TB, which substantially affects the disease's development. The review summarizes the functions and mechanisms of M. tb acetyltransferase in virulence and drug resistance. It also discusses the role and mechanism of M. tb in regulating host protein acetylation and immune response regulation. Furthermore, the current scenario of isoniazid usage in M. tb therapy treatment is examined. Overall, this review provides valuable information that can serve as a preliminary basis for studying pathogenic research, developing new drugs, exploring in-depth drug resistance mechanisms, and providing precise treatment for TB.

N-Succinyltransferase Encoded by a Cryptic Siderophore Biosynthesis Gene Cluster in Streptomyces Modifies Structurally Distinct Antibiotics

The antibiotic desertomycin A and its previously undescribed inactive N-succinylated analogue, desertomycin X, were isolated from Streptomyces sp. strain YIM 121038. Genome sequencing and analysis readily identified the desertomycin biosynthetic gene cluster (BGC), which lacked genes encoding acyltransferases that would account for desertomycin X formation. Scouting the genome for putative N-acyltransferase genes led to the identification of a candidate within a cryptic siderophore BGC (csb) encoding a putative homologue of the N6'-hydroxylysine acetyltransferase IucB. Expression of the codon-optimized gene designated csbC in Escherichia coli yielded the recombinant protein that was able to N-succinylate desertomycin A as well as several other structurally distinct antibiotics harboring amino groups. Some antibiotics were rendered antibiotically inactive due to the CsbC-catalyzed succinylation in vitro. Unlike many known N-acyltransferases involved in antibiotic resistance, CsbC could not efficiently acetylate the same antibiotics. When expressed in E. coli, CsbC provided low-level resistance to kanamycin and ampicillin, suggesting that it may play a role in antibiotic resistance in natural habitats, where the concentration of antibiotics is usually low. IMPORTANCE In their natural habitats, bacteria encounter a plethora of organic compounds, some of which may be represented by antibiotics produced by certain members of the microbial community. A number of antibiotic resistance mechanisms have been described, including those specified by distinct genes encoding proteins that degrade, modify, or expel antibiotics. In this study, we report identification and characterization of an enzyme apparently involved in the biosynthesis of a siderophore, but also having the ability of modify and thereby inactivate a wide variety of structurally diverse antibiotics. This discovery sheds light on additional capabilities of bacteria to withstand antibiotic treatment and suggests that enzymes involved in secondary metabolism may have an additional function in the natural environment.

A Phagosomally Expressed Gene, rv0428c, of Mycobacterium tuberculosis Demonstrates Acetyl Transferase Activity and Plays a Protective Role Under Stress Conditions

Mycobacterium tuberculosis genome is composed of several hypothetical gene products that need to be characterized for understanding the physiology of bacteria. Rv0428c was one of the 11 proteins exclusively identified within the phagosomal compartment of macrophages infected with mycobacteria and marked as hypothetical. The expression of rv0428c gene was upregulated under acidic and nutritive stress conditions in M. tuberculosis H37Ra, which was supported by potential sigma factor binding sites in the region upstream to the rv0428c gene. The bioinformatics analysis predicted it to be a GCN5- acetyl transferase, belonging to the Histone acetyl transferase (HAT) family. The docking analysis predicted formation of hydrogen bonds and hydrophobic interactions between donor acetyl-co-A and histone H3 tail region. rv0428c gene was cloned and expressed in E. coli. The protein was purified to homogeneity and was fairly stable over a wide range of pH 5.0–9.0 and temperature up to 40 °C. The HAT activity of purified Rv0428c was confirmed by in vitro acetylation assay using recombinant H3 histone expressed in bacteria as substrate, which increased in time dependent manner. The results suggested that it is the second confirmed acetyl transferase in M. tuberculosis H37Rv. Furthermore, rv0428c was over expressed in surrogate host M. smegmatis, which led to enhanced growth rate and altered colony morphology. The expression of rv0428c in M. smegmatis promoted the survival of bacteria under acidic and nutritive stress conditions. In conclusion, Rv0428c, a phagosomal acetyl transferase of M. tuberculosis, might be involved in survival under stress conditions.

Identification and characterization of a novel GNAT superfamily Nα -acetyltransferase from Salinicoccus halodurans H3B36

N^α -acetyl-α-lysine was found as a new type of compatible solutes that acted as an organic cytoprotectant in the strain of Salinicoccus halodurans H3B36. A novel lysine N^α -acetyltransferase gene (shkat), encoding an enzyme that catalysed the acetylation of lysine exclusively at α position, was identified from this moderate halophilic strain and expressed in Escherichia coli. Sequence analysis indicated ShKAT contained a highly conserved pyrophosphate-binding loop (Arg-Gly-Asn-Gly-Asn-Gly), which was a signature of the GNAT superfamily. ShKAT exclusively recognized free amino acids as substrate, including lysine and other basic amino acids. The enzyme showed a wide range of optimal pH value and was tolerant to high-alkali and high-salinity conditions. As a new member of the GNAT superfamily, the ShKAT was the first enzyme recognized free lysine as substrate. We believe this work gives an expanded perspective of the GNAT superfamily, and reveals great potential of the shkat gene to be applied in genetic engineering for resisting extreme conditions.