A single regulator NrtR controls bacterial NAD+ homeostasis via its acetylation

NAD+ supplementation improves mitochondrial functions and normalizes glaucomatous trabecular meshwork features

Glaucoma is characterized by pathological elevation of intraocular pressure (IOP) due to dysfunctional trabecular meshwork (TM), which is the primary cause of irreversible vision loss. There are currently no effective treatment strategies for glaucoma. Mitochondrial function plays a crucial role in regulating IOP within the TM. In this study, primary TM cells treated with dexamethasone were used to simulate glaucomatous changes, showing abnormal cellular cytoskeleton, increased expression of extracellular matrix, and disrupted mitochondrial fusion and fission dynamics. Furthermore, glaucomatous TM cell line GTM3 exhibited impaired mitochondrial membrane potential and phagocytic function, accompanied by decreased oxidative respiratory levels as compared to normal TM cells iHTM. Mechanistically, lower NAD + levels in GTM3, possibly associated with increased expression of key enzymes CD38 and PARP1 related to NAD + consumption, were observed. Supplementation of NAD + restored mitochondrial function and cellular viability in GTM3 cells. Therefore, we propose that the aberrant mitochondrial function in glaucomatous TM cells may be attributed to increased NAD + consumption dependent on CD38 and PARP1, and NAD + supplementation could effectively ameliorate mitochondrial function and improve TM function, providing a novel alternative approach for glaucoma treatment.

Chasing the landscape for intrahospital transmission and evolution of hypervirulent carbapenem-resistant Klebsiella pneumoniae

The spread of hypervirulent carbapenem-resistant Klebsiella pneumoniae (Hv-CRKP) is a global health concern. Here, we report the intrahospital colonization and spread of Hv-CRKP isolates in a tertiary hospital from 2017 to 2022. Analyses of 90 nonredundant CRKP isolates from 72 patients indicated that Hv-CRKP transferability relies on the dominant ST11-K64 clone. Whole-genome sequencing of 11 representative isolates gave 31 complete plasmid sequences, including 12 KPC-2 resistance carriers and 10 RmpA virulence vehicles. Apart from the binary vehicles, we detected two types of fusion plasmids, favoring the cotransfer of RmpA virulence and KPC-2 resistance. The detection of ancestry/relic plasmids enabled us to establish genetic mechanisms by which rare fusion plasmids form. Unexpectedly, we found a total of five rmpA promoter variants (P9T-P13T) exhibiting distinct activities and varying markedly in their geographic distributions. CRISPR/Cas9 manipulation confirmed that an active PT11-rmpA regulator is a biomarker for the "high-risk" ST11-K64/CRKP clone. These findings suggest clonal spread and clinical evolution of the prevalent ST11-K64/Hv-CRKP clones. Apart from improved public awareness of Hv-CRKP convergence, our findings might benefit the development of surveillance (and/or intervention) strategies for the dominant ST11-K64 lineage of the Hv-CRKP population in healthcare sectors.

Adenosine triphosphate can act as a determinant of lysine acetylation of non-native and native substrates

The protein lysine acetylation includes acetyl-CoA (AcCoA) or acetyl phosphate (AcP)-mediated nonenzymatic acetylation, and enzymatic acetylation. It is widespread in the proteomes but the acetylation levels of most sites are very low. A thorough understanding of the determinants of low acetylation levels is highly important for elucidating the physiological relevance of lysine acetylation. In this study, we constructed a non-native substrate library containing 24 synthesized polypeptides, and we showed that ATP could inhibit the AcCoA-mediated nonenzymatic acetylation of these polypeptides through LC-MS/MS analysis. The acetyltransferase PatZ could acetylated these non-native substrates, and the PatZ-catalyzed acetylation of the polypeptides was also inhibited by ATP. Furthermore, the Western blot showed that ATP also inhibited the nonenzymatic (AcCoA or AcP-mediated) and enzymatic (PatZ-catalyzed) acetylation of acetyl-CoA synthetase Acs, which is a native substrate for acetylation. ATP can also inhibit the autoacetylation of acetyltransferase PatZ. Besides, both ADP and AMP could enhance the AcP-mediated acetylation of Acs, but ADP slightly inhibited the AcCoA-mediated acetylation of Acs. However, both ADP and AMP had no evident inhibition on the PatZ-catalyzed acetylation of Acs. Based on these results, we proposed that ATP can act as an inhibitor of acetylation, and it may regulate the function of PatZ by inhibiting its autoacetylation and compensate for the function of deacetylase CobB.

New biochemistry in the Rhodanese-phosphatase superfamily: emerging roles in diverse metabolic processes, nucleic acid modifications, and biological conflicts

The protein-tyrosine/dual-specificity phosphatases and rhodanese domains constitute a sprawling superfamily of Rossmannoid domains that use a conserved active site with a cysteine to catalyze a range of phosphate-transfer, thiotransfer, selenotransfer and redox activities. While these enzymes have been extensively studied in the context of protein/lipid head group dephosphorylation and various thiotransfer reactions, their overall diversity and catalytic potential remain poorly understood. Using comparative genomics and sequence/structure analysis, we comprehensively investigate and develop a natural classification for this superfamily. As a result, we identified several novel clades, both those which retain the catalytic cysteine and those where a distinct active site has emerged in the same location (e.g. diphthine synthase-like methylases and RNA 2' OH ribosyl phosphate transferases). We also present evidence that the superfamily has a wider range of catalytic capabilities than previously known, including a set of parallel activities operating on various sugar/sugar alcohol groups in the context of NAD+-derivatives and RNA termini, and potential phosphate transfer activities involving sugars and nucleotides. We show that such activities are particularly expanded in the RapZ-C-DUF488-DUF4326 clade, defined here for the first time. Some enzymes from this clade are predicted to catalyze novel DNA-end processing activities as part of nucleic-acid-modifying systems that are likely to function in biological conflicts between viruses and their hosts.

Acetylation of Cyclic AMP Receptor Protein by Acetyl Phosphate Modulates Mycobacterial Virulence

The success of Mycobacterium tuberculosis (Mtb) as a pathogen is partly attributed to its ability to sense and respond to dynamic host microenvironments. The cyclic AMP (cAMP) receptor protein (CRP) is closely related to the pathogenicity of Mtb and plays an important role in this process. However, the molecular mechanisms guiding the autoregulation and downstream target genes of CRP while Mtb responds to its environment are not fully understood. Here, it is demonstrated that the acetylation of conserved lysine 193 (K193) within the C-terminal DNA-binding domain of CRP reduces its DNA-binding ability and inhibits transcriptional activity. The reversible acetylation status of CRP K193 was shown to significantly affect mycobacterial growth phenotype, alter the stress response, and regulate the expression of biologically relevant genes using a CRP K193 site-specific mutation. Notably, the acetylation level of K193 decreases under CRP-activating conditions, including the presence of cAMP, low pH, high temperature, and oxidative stress, suggesting that microenvironmental signals can directly regulate CRP K193 acetylation. Both cell- and murine-based infection assays confirmed that CRP K193 is critical to the regulation of Mtb virulence. Furthermore, the acetylation of CRP K193 was shown to be dependent on the intracellular metabolic intermediate acetyl phosphate (AcP), and deacetylation was mediated by NAD⁺-dependent deacetylases. These findings indicate that AcP-mediated acetylation of CRP K193 decreases CRP activity and negatively regulates the pathogenicity of Mtb. We believe that the underlying mechanisms of cross talk between transcription, posttranslational modifications, and metabolites are a common regulatory mechanism for pathogenic bacteria. IMPORTANCE Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis, and the ability of Mtb to survive harsh host conditions has been the subject of intensive research. As a result, we explored the molecular mechanisms guiding downstream target genes of CRP when Mtb responds to its environment. Our study makes a contribution to the literature because we describe the role of acetylated K193 in regulating its binding affinity to target DNA and influencing the virulence of mycobacteria. We discovered that mycobacteria can regulate their pathogenicity through the reversible acetylation of CRP K193 and that this reversible acetylation is mediated by AcP and a NAD⁺-dependent deacetylase. The regulation of CRP_Mtb by posttranslational modifications, at the transcriptional level, and by metabolic intermediates contribute to a better understanding of its role in the survival and pathogenicity of mycobacteria.

Bacterial NadQ (COG4111) is a Nudix-like, ATP-responsive regulator of NAD biosynthesis

Nicotinamide-adenine dinucleotide (NAD) is centrally important to metabolic reactions that involve redox chemistry. In bacteria, NAD biosynthesis is controlled by different transcription factors, depending on the species. Among the four regulators identified so far, the protein NadQ is reported to act as a repressor of the de novo NAD biosynthetic pathway in proteobacteria. Using comparative genomics, a systematic reconstruction of NadQ regulons in thousands of fully sequenced bacterial genomes has been performed, confirming that NadQ is present in α-proteobacteria and some β- and γ-proteobacteria, including pathogens like Bordetella pertussis and Neisseria meningitidis, where it likely controls de novo NAD biosynthesis. Through mobility shift assay and mutagenesis, the DNA binding activity of NadQ from Agrobacterium tumefaciens was experimentally validated and determined to be suppressed by ATP. The crystal structures of NadQ in native form and in complex with ATP were determined, indicating that NadQ is a dimer, with each monomer composed of an N-terminal Nudix domain hosting the effector binding site and a C-terminal winged helix-turn-helix domain that binds DNA. Within the dimer, we found one ATP molecule bound, at saturating concentration of the ligand, in keeping with an intrinsic asymmetry of the quaternary structure. Overall, this study provided the basis for depicting a working model of NadQ regulation mechanism.

Apprehending the NAD+–ADPr-Dependent Systems in the Virus World

NAD⁺ and ADP-ribose (ADPr)-containing molecules are at the interface of virus–host conflicts across life encompassing RNA processing, restriction, lysogeny/dormancy and functional hijacking. We objectively defined the central components of the NAD⁺–ADPr networks involved in these conflicts and systematically surveyed 21,191 completely sequenced viral proteomes representative of all publicly available branches of the viral world to reconstruct a comprehensive picture of the viral NAD⁺–ADPr systems. These systems have been widely and repeatedly exploited by positive-strand RNA and DNA viruses, especially those with larger genomes and more intricate life-history strategies. We present evidence that ADP-ribosyltransferases (ARTs), ADPr-targeting Macro, NADAR and Nudix proteins are frequently packaged into virions, particularly in phages with contractile tails (Myoviruses), and deployed during infection to modify host macromolecules and counter NAD⁺-derived signals involved in viral restriction. Genes encoding NAD⁺–ADPr-utilizing domains were repeatedly exchanged between distantly related viruses, hosts and endo-parasites/symbionts, suggesting selection for them across the virus world. Contextual analysis indicates that the bacteriophage versions of ADPr-targeting domains are more likely to counter soluble ADPr derivatives, while the eukaryotic RNA viral versions might prefer macromolecular ADPr adducts. Finally, we also use comparative genomics to predict host systems involved in countering viral ADP ribosylation of host molecules.

NrtR Mediated Regulation of H1-T6SS in Pseudomonas aeruginosa

NrtR is a Nudix-related transcriptional regulator that is distributed among diverse bacteria and plays an important role in modulating bacterial intracellular NAD homeostasis. Previously, we showed that NrtR influences the T3SS expression and pathogenesis of Pseudomonas aeruginosa and demonstrated that NrtR mediates T3SS regulation through the cAMP/Vfr pathway. In the present study, we found that mutation of the nrtR gene leads to upregulation of the Hcp secretion island-I type VI secretion system (H1-T6SS). Further analysis revealed that mutation of the nrtR gene results in upregulation of regulatory RNAs (RsmY/RsmZ) that are known to control the H1-T6SS by sequestration of RsmA or RsmN. Simultaneous deletion of rsmY/rsmZ reduced the expression of H1-T6SS in the ΔnrtR mutant. In addition, overexpression of either rsmA or rsmN in ΔnrtR decreased H1-T6SS expression. Chromatin immunoprecipitation (ChIP)-Seq and electrophoretic mobility shift assay (EMSA) analyses revealed that NrtR directly binds to the promoters of rsmY, rsmZ and tssA1 (first gene of the H1-T6SS operon). Overall, the results from this study reveal the molecular details of NrtR-mediated regulation of H1-T6SS in P. aeruginosa.

IMPORTANCE NrtR is a Nudix-related transcriptional regulator and controls the NAD cofactor biosynthesis in bacteria. P. aeruginosa NrtR binds to the intergenic region between nadD2 and pcnA to repress the expression of the two operons, therefore controlling the NAD biosynthesis. We have previously reported that NrtR controls T3SS expression via the cAMP/Vfr pathway in P. aeruginosa. However, the global regulatory function and direct binding targets of the NrtR remain elusive in P. aeruginosa. This study reveals novel direct regulatory targets of the NrtR in P. aeruginosa, elucidating the molecular mechanism of NrtR-mediated regulation of H1-T6SS.

A catalogue of signal molecules that interact with sensor kinases, chemoreceptors and transcriptional regulators

Bacteria have evolved many different signal transduction systems that sense signals and generate a variety of responses. Generally, most abundant are transcriptional regulators, sensor histidine kinases and chemoreceptors. Typically, these systems recognize their signal molecules with dedicated ligand-binding domains (LBDs), which, in turn, generate a molecular stimulus that modulates the activity of the output module. There are an enormous number of different LBDs that recognize a similarly diverse set of signals. To give a global perspective of the signals that interact with transcriptional regulators, sensor kinases and chemoreceptors, we manually retrieved information on the protein-ligand interaction from about 1,200 publications and 3D structures. The resulting 811 proteins were classified according to the Pfam family into 127 groups. These data permit a delineation of the signal profiles of individual LBD families as well as distinguishing between families that recognize signals in a promiscuous manner and those that possess a well-defined ligand range. A major bottleneck in the field is the fact that the signal input of many signaling systems is unknown. The signal repertoire reported here will help the scientific community design experimental strategies to identify the signaling molecules for uncharacterised sensor proteins.

Integrated mass spectrometry-based multi-omics for elucidating mechanisms of bacterial virulence

Despite being considered the simplest form of life, bacteria remain enigmatic, particularly in light of pathogenesis and evolving antimicrobial resistance. After three decades of genomics, we remain some way from understanding these organisms, and a substantial proportion of genes remain functionally unknown. Methodological advances, principally mass spectrometry (MS), are paving the way for parallel analysis of the proteome, metabolome and lipidome. Each provides a global, complementary assay, in addition to genomics, and the ability to better comprehend how pathogens respond to changes in their internal (e.g. mutation) and external environments consistent with infection-like conditions. Such responses include accessing necessary nutrients for survival in a hostile environment where co-colonizing bacteria and normal flora are acclimated to the prevailing conditions. Multi-omics can be harnessed across temporal and spatial (sub-cellular) dimensions to understand adaptation at the molecular level. Gene deletion libraries, in conjunction with large-scale approaches and evolving bioinformatics integration, will greatly facilitate next-generation vaccines and antimicrobial interventions by highlighting novel targets and pathogen-specific pathways. MS is also central in phenotypic characterization of surface biomolecules such as lipid A, as well as aiding in the determination of protein interactions and complexes. There is increasing evidence that bacteria are capable of widespread post-translational modification, including phosphorylation, glycosylation and acetylation; with each contributing to virulence. This review focuses on the bacterial genotype to phenotype transition and surveys the recent literature showing how the genome can be validated at the proteome, metabolome and lipidome levels to provide an integrated view of organism response to host conditions.

Identification of a Toxin-Antitoxin System That Contributes to Persister Formation by Reducing NAD in Pseudomonas aeruginosa

Bacterial persisters are slow-growing or dormant cells that are highly tolerant to bactericidal antibiotics and contribute to recalcitrant and chronic infections. Toxin/antitoxin (TA) systems play important roles in controlling persister formation. Here, we examined the roles of seven predicted type II TA systems in the persister formation of a Pseudomonas aeruginosa wild-type strain PA14. Overexpression of a toxin gene PA14_51010 or deletion of the cognate antitoxin gene PA14_51020 increased the bacterial tolerance to antibiotics. Co-overexpression of PA14_51010 and PA14_51020 or simultaneous deletion of the two genes resulted in a wild-type level survival rate following antibiotic treatment. The two genes were located in the same operon that was repressed by PA14_51020. We further demonstrated the interaction between PA14_51010 and PA14_51020. Sequence analysis revealed that PA14_51010 contained a conserved RES domain. Overexpression of PA14_51010 reduced the intracellular level of nicotinamide adenine dinucleotide (NAD⁺). Mutation of the RES domain abolished the abilities of PA14_51010 in reducing NAD⁺ level and promoting persister formation. In addition, overproduction of NAD⁺ by mutation in an nrtR gene counteracted the effect of PA14_51010 overexpression in promoting persister formation. In combination, our results reveal a novel TA system that contributes to persister formation through reducing the intracellular NAD⁺ level in P. aeruginosa.

Individual Nudix hydrolases affect diverse features of Pseudomonas aeruginosa

Nudix proteins catalyze the hydrolysis of pyrophosphate bonds in a variety of substrates and are ubiquitous in all domains of life. The genome of an important opportunistic human pathogen, Pseudomonas aeruginosa, encodes multiple Nudix proteins. To determine the role of nine Nudix hydrolases of the P. aeruginosa PAO1161 strain in its fitness, virulence or antibiotic resistance mutants devoid of individual enzymes were constructed and analyzed for growth rate, motility, biofilm formation, pyocyanin production, and susceptibility to oxidative stress and different antibiotics. The potential effect on bacterial virulence was studied using the Caenorhabditis elegans-P. aeruginosa infection model. Of the nine mutants tested, five had an altered phenotype in comparison with the wild-type strain. The ΔPA3470, ΔPA3754, and ΔPA4400 mutants showed increased pyocyanin production, were more resistant to the β-lactam antibiotic piperacillin, and were more sensitive to killing by H2 O2 . In addition, ΔPA4400 and ΔPA5176 had impaired swarming motility and were less virulent for C. elegans. The ΔPA4841 had an increased sensitivity to oxidative stress. These changes were reversed by providing the respective nudix gene in trans indicating that the observed phenotype alterations were indeed due to the lack of the particular Nudix protein.