Allosteric pyruvate kinase-based "logic gate" synergistically senses energy and sugar levels in Mycobacterium tuberculosis

Structural Basis of Nucleotide Selectivity in Pyruvate Kinase

Nucleoside triphosphates are indispensable in numerous biological processes, with enzymes involved in their biogenesis playing pivotal roles in cell proliferation. Pyruvate kinase (PYK), commonly regarded as the terminal glycolytic enzyme that generates ATP in tandem with pyruvate, is also capable of synthesizing a wide range of nucleoside triphosphates from their diphosphate precursors. Despite their substrate promiscuity, some PYKs show preference towards specific nucleotides, suggesting an underlying mechanism for differentiating nucleotide bases. However, the thorough characterization of this mechanism has been hindered by the paucity of nucleotide-bound PYK structures. Here, we present crystal structures of Streptococcus pneumoniae PYK in complex with four different nucleotides. These structures facilitate direct comparison of the protein-nucleotide interactions and offer structural insights into its pronounced selectivity for GTP synthesis. Notably, this selectivity is dependent on a sequence motif in the nucleotide recognition site that is widely present among prokaryotic PYKs, particularly in Firmicutes species. We show that pneumococcal cell growth is significantly impaired when expressing a PYK variant with compromised GTP and UTP synthesis activity, underscoring the importance of PYK in maintaining nucleotide homeostasis. Our findings collectively advance our understanding of PYK biochemistry and prokaryotic metabolism.

Allosteric Regulation of Pyruvate Kinase Enables Efficient and Robust Gluconeogenesis by Preventing Metabolic Conflicts and Carbon Overflow

Glycolysis and gluconeogenesis are reciprocal metabolic pathways that utilize different carbon sources. Pyruvate kinase catalyzes the irreversible final step of glycolysis, yet the physiological function of its regulation is poorly understood. Through metabolomics and enzyme kinetics studies, we discovered that pyruvate kinase activity is inhibited during gluconeogenesis in the soil bacterium Bacillus subtilis . This regulation involves an extra C-terminal domain (ECTD) of pyruvate kinase, which is essential for autoinhibition and regulation by metabolic effectors. Introducing a pyruvate kinase mutant lacking the ECTD into B. subtilis resulted in defects specifically under gluconeogenic conditions, including inefficient carbon utilization, slower growth, and decreased resistance to the herbicide glyphosate. These defects are not caused by the phosphoenolpyruvate-pyruvate-oxaloacetate futile cycle. Instead, we identified two significant metabolic consequences of pyruvate kinase dysregulation during gluconeogenesis: increased carbon overflow into the medium and failure to expand glycolytic intermediates such as phosphoenolpyruvate (PEP). In silico analysis revealed that in wild-type cells, an expanded PEP pool enabled by pyruvate kinase regulation is critical for the thermodynamic feasibility of gluconeogenesis. Our findings underscore the importance of allosteric regulation during gluconeogenesis in coordinating metabolic flux, efficient energy utilization, and antimicrobial resistance.

Electron transport chain capacity expands yellow fever vaccine immunogenicity

Vaccination has successfully controlled several infectious diseases although better vaccines remain desirable. Host response to vaccination studies have identified correlates of vaccine immunogenicity that could be useful to guide development and selection of future vaccines. However, it remains unclear whether these findings represent mere statistical correlations or reflect functional associations with vaccine immunogenicity. Functional associations, rather than statistical correlates, would offer mechanistic insights into vaccine-induced adaptive immunity. Through a human experimental study to test the immunomodulatory properties of metformin, an anti-diabetic drug, we chanced upon a functional determinant of neutralizing antibodies. Although vaccine viremia is a known correlate of antibody response, we found that in healthy volunteers with no detectable or low yellow fever 17D viremia, metformin-treated volunteers elicited higher neutralizing antibody titers than placebo-treated volunteers. Transcriptional and metabolomic analyses collectively showed that a brief course of metformin, started 3 days prior to YF17D vaccination and stopped at 3 days after vaccination, expanded oxidative phosphorylation and protein translation capacities. These increased capacities directly correlated with YF17D neutralizing antibody titers, with reduced reactive oxygen species response compared to placebo-treated volunteers. Our findings thus demonstrate a functional association between cellular respiration and vaccine-induced humoral immunity and suggest potential approaches to enhancing vaccine immunogenicity.

A three-level regulatory mechanism of the aldo-keto reductase subfamily AKR12D

Modulation of protein function through allosteric regulation is central in biology, but biomacromolecular systems involving multiple subunits and ligands may exhibit complex regulatory mechanisms at different levels, which remain poorly understood. Here, we discover an aldo-keto reductase termed AKRtyl and present its three-level regulatory mechanism. Specifically, by combining steady-state and transient kinetics, X-ray crystallography and molecular dynamics simulation, we demonstrate that AKRtyl exhibits a positive synergy mediated by an unusual Monod-Wyman-Changeux (MWC) paradigm of allosteric regulation at low concentrations of the cofactor NADPH, but an inhibitory effect at high concentrations is observed. While the substrate tylosin binds at a remote allosteric site with positive cooperativity. We further reveal that these regulatory mechanisms are conserved in AKR12D subfamily, and that substrate cooperativity is common in AKRs across three kingdoms of life. This work provides an intriguing example for understanding complex allosteric regulatory networks.

What is allosteric regulation? Exploring the exceptions that prove the rule!

"Allosteric" was first introduced to mean the other site (i.e., a site distinct from the active or orthosteric site), an adjective for "regulation" to imply a regulatory outcome resulting from ligand binding at another site. That original idea outlines a system with two ligand-binding events at two distinct locations on a macromolecule (originally a protein system), which defines a four-state energy cycle. An allosteric energy cycle provides a quantifiable allosteric coupling constant and focuses our attention on the unique properties of the four equilibrated protein complexes that constitute the energy cycle. Because many observed phenomena have been referenced as "allosteric regulation" in the literature, the goal of this work is to use literature examples to explore which systems are and are not consistent with the two-ligand thermodynamic energy cycle-based definition of allosteric regulation. We emphasize the need for consistent language so comparisons can be made among the ever-increasing number of allosteric systems. Building on the mutually exclusive natures of an energy cycle definition of allosteric regulation versus classic two-state models, we conclude our discussion by outlining how the often-proposed Rube-Goldberg-like mechanisms are likely inconsistent with an energy cycle definition of allosteric regulation.

Allosteric communication and signal transduction in proteins

Allostery is one of the cornerstones of biological function, as it plays a fundamental role in regulating protein activity. The modelling of allostery has gradually moved from a conformation-based framework, linked to structural changes, to dynamics-based allostery, whereby the effects of ligand binding propagate via signal transduction from the allosteric site to other regions of the protein via inter-residue interactions. Characterising such allosteric signalling pathways, which do not necessarily lead to conformational changes, has been pursued experimentally and complemented by computational analysis of protein networks to detect subtle dynamic propagation paths. Considering allostery from the perspective of signal transduction broadens the understanding of allosteric mechanisms, underscores the importance of protein topology, and can provide insights into allosteric drug design.

Bactericidal bissulfone B7 targets bacterial pyruvate kinase to impair bacterial biology and pathogenicity in plants

The prevention and control of rice bacterial leaf blight (BLB) disease has not yet been achieved due to the lack of effective agrochemicals and available targets. Herein, we develop a series of novel bissulfones and a novel target with a unique mechanism to address this challenge. The developed bissulfones can control Xanthomonas oryzae pv. oryzae (Xoo), and 2-(bis(methylsulfonyl)methylene)-N-(4-chlorophenyl) hydrazine-1-carboxamide (B7) is more effective than the commercial drugs thiodiazole copper (TC) and bismerthiazol (BT). Pyruvate kinase (PYK) in Xoo has been identified for the first time as the target protein of our bissulfone B7. PYK modulates bacterial virulence via a CRP-like protein (Clp)/two-component system regulatory protein (regR) axis. The elucidation of this pathway facilitates the use of B7 to reduce PYK expression at the transcriptional level, block PYK activity at the protein level, and impair the interaction within the PYK-Clp-regR complex via competitive inhibition, thereby attenuating bacterial biology and pathogenicity. This study offers insights into the molecular and mechanistic aspects underlying anti-Xoo strategies that target PYK. We believe that these valuable discoveries will be used for bacterial disease control in the future.

A conserved transcription factor controls gluconeogenesis via distinct targets in hypersaline-adapted archaea with diverse metabolic capabilities

Timely regulation of carbon metabolic pathways is essential for cellular processes and to prevent futile cycling of intracellular metabolites. In Halobacterium salinarum, a hypersaline adapted archaeon, a sugar-sensing TrmB family protein controls gluconeogenesis and other biosynthetic pathways. Notably, Hbt. salinarum does not utilize carbohydrates for energy, uncommon among Haloarchaea. We characterized a TrmB-family transcriptional regulator in a saccharolytic generalist, Haloarcula hispanica, to investigate whether the targets and function of TrmB, or its regulon, is conserved in related species with distinct metabolic capabilities. In Har. hispanica, TrmB binds to 15 sites in the genome and induces the expression of genes primarily involved in gluconeogenesis and tryptophan biosynthesis. An important regulatory control point in Hbt. salinarum, activation of ppsA and repression of pykA, is absent in Har. hispanica. Contrary to its role in Hbt. salinarum and saccharolytic hyperthermophiles, TrmB does not act as a global regulator: it does not directly repress the expression of glycolytic enzymes, peripheral pathways such as cofactor biosynthesis, or catabolism of other carbon sources in Har. hispanica. Cumulatively, these findings suggest rewiring of the TrmB regulon alongside metabolic network evolution in Haloarchaea.

Metabolism of glucose activates TORC1 through multiple mechanisms in Saccharomyces cerevisiae

Target of Rapamycin Complex 1 (TORC1) is a conserved eukaryotic protein complex that links the presence of nutrients with cell growth. In Saccharomyces cerevisiae, TORC1 activity is positively regulated by the presence of amino acids and glucose in the medium. However, the mechanisms underlying nutrient-induced TORC1 activation remain poorly understood. By utilizing an in vivo TORC1 activation assay, we demonstrate that differential metabolism of glucose activates TORC1 through three distinct pathways in yeast. The first "canonical Rag guanosine triphosphatase (GTPase)-dependent pathway" requires conversion of glucose to fructose 1,6-bisphosphate, which activates TORC1 via the Rag GTPase heterodimer Gtr1GTP-Gtr2GDP. The second "non-canonical Rag GTPase-dependent pathway" requires conversion of glucose to glucose 6-phosphate, which activates TORC1 via a process that involves Gtr1GTP-Gtr2GTP and mitochondrial function. The third "Rag GTPase-independent pathway" requires complete glycolysis and vacuolar ATPase reassembly for TORC1 activation. We have established a roadmap to deconstruct the link between glucose metabolism and TORC1 activation.

Programming conformational cooperativity to regulate allosteric protein-oligonucleotide signal transduction

Conformational cooperativity is a universal molecular effect mechanism and plays a critical role in signaling pathways. However, it remains a challenge to develop artificial molecular networks regulated by conformational cooperativity, due to the difficulties in programming and controlling multiple structural interactions. Herein, we develop a cooperative strategy by programming multiple conformational signals, rather than chemical signals, to regulate protein-oligonucleotide signal transduction, taking advantage of the programmability of allosteric DNA constructs. We generate a cooperative regulation mechanism, by which increasing the loop lengths at two different structural modules induced the opposite effects manifesting as down- and up-regulation. We implement allosteric logic operations by using two different proteins. Further, in cell culture we demonstrate the feasibility of this strategy to cooperatively regulate gene expression of PLK1 to inhibit tumor cell proliferation, responding to orthogonal protein-signal stimulation. This programmable conformational cooperativity paradigm has potential applications in the related fields.

Functional and structural characterization of Streptococcus pneumoniae pyruvate kinase involved in fosfomycin resistance

Glycolysis is the primary metabolic pathway in the strictly fermentative Streptococcus pneumoniae, which is a major human pathogen associated with antibiotic resistance. Pyruvate kinase (PYK) is the last enzyme in this pathway that catalyzes the production of pyruvate from phosphoenolpyruvate (PEP) and plays a crucial role in controlling carbon flux; however, while S. pneumoniae PYK (SpPYK) is indispensable for growth, surprisingly little is known about its functional properties. Here, we report that compromising mutations in SpPYK confer resistance to the antibiotic fosfomycin, which inhibits the peptidoglycan synthesis enzyme MurA, implying a direct link between PYK and cell wall biogenesis. The crystal structures of SpPYK in the apo and ligand-bound states reveal key interactions that contribute to its conformational change as well as residues responsible for the recognition of PEP and the allosteric activator fructose 1,6-bisphosphate (FBP). Strikingly, FBP binding was observed at a location distinct from previously reported PYK effector binding sites. Furthermore, we show that SpPYK could be engineered to become more responsive to glucose 6-phosphate instead of FBP by sequence and structure-guided mutagenesis of the effector binding site. Together, our work sheds light on the regulatory mechanism of SpPYK and lays the groundwork for antibiotic development that targets this essential enzyme.

PYK-SubstitutionOME: an integrated database containing allosteric coupling, ligand affinity and mutational, structural, pathological, bioinformatic and computational information about pyruvate kinase isozymes

Interpreting changes in patient genomes, understanding how viruses evolve and engineering novel protein function all depend on accurately predicting the functional outcomes that arise from amino acid substitutions. To that end, the development of first-generation prediction algorithms was guided by historic experimental datasets. However, these datasets were heavily biased toward substitutions at positions that have not changed much throughout evolution (i.e. conserved). Although newer datasets include substitutions at positions that span a range of evolutionary conservation scores, these data are largely derived from assays that agglomerate multiple aspects of function. To facilitate predictions from the foundational chemical properties of proteins, large substitution databases with biochemical characterizations of function are needed. We report here a database derived from mutational, biochemical, bioinformatic, structural, pathological and computational studies of a highly studied protein family-pyruvate kinase (PYK). A centerpiece of this database is the biochemical characterization-including quantitative evaluation of allosteric regulation-of the changes that accompany substitutions at positions that sample the full conservation range observed in the PYK family. We have used these data to facilitate critical advances in the foundational studies of allosteric regulation and protein evolution and as rigorous benchmarks for testing protein predictions. We trust that the collected dataset will be useful for the broader scientific community in the further development of prediction algorithms. Database URL https://github.com/djparente/PYK-DB.

Analysis of Akkermansia muciniphila in Mulberry Galacto-Oligosaccharide Medium via Comparative Transcriptomics

Akkermansia muciniphila is a common member of the human gut microbiota and belongs to the phylum Verrucomicrobia. Decreased levels of A. muciniphila are associated with many diseases, so it is thought to be a beneficial resident of the intestinal mucosal layer. In this study, we found that different prebiotics promoted the proliferation of A. muciniphila, and mulberry galacto-oligosaccharide (MGO) had the greatest effect. We cultured A. muciniphila in a brian heart infusion (BHI) medium containing 5% galactooligosaccharides (GOS), mulberry polysaccharide solution (MPS), and MGO, and transcriptomic analyses were performed. The results revealed that, after 6 days of cultivation, the numbers of upregulated functional genes (based on Gene Ontology) were approximately 0.7 and 19% higher with MPS and MGO, respectively, than with GOS. Analysis using the Kyoto Encyclopedia of Genes and Genomes showed that, when A. muciniphila was cultured with MGO, genes that were upregulated were enriched in the carbohydrate metabolism, the metabolism of cofactors and vitamins, the energy metabolism, the amino acid metabolism, and the lipid metabolism. Upregulated genes included galM and pfkA in the galactose metabolism, and pgi, pfk, fbaA, tpiA, gapA, pgk, gpml, eno, pyk, and lpd in the glycolysis/gluconeogenesis pathway. Real-time quantitative PCR results were consistent with the RNA-Seq data. This work provides valuable knowledge which can be available for the functional application of A. muciniphila and MGO.

PKM2 deficiency exacerbates gram-negative sepsis-induced cardiomyopathy via disrupting cardiac calcium homeostasis

Sepsis is a life-threatening syndrome with multi-organ dysfunction in critical care medicine. With the occurrence of sepsis-induced cardiomyopathy (SIC), characterized by reduced ventricular contractility, the mortality of sepsis is boosted to 70-90%. Pyruvate kinase M2 (PKM2) functions in a variety of biological processes and diseases other than glycolysis, and has been documented as a cardioprotective factor in several heart diseases. It is currently unknown whether PKM2 influences the development of SIC. Here, we found that PKM2 was upregulated in cardiomyocytes treated with LPS both in vitro and in vivo. Pkm2 inhibition exacerbated the LPS-induced cardiac damage to neonatal rat cardiomyocytes (NRCMs). Furthermore, cardiomyocytes lacking PKM2 aggravated LPS-induced cardiomyopathy, including myocardial damage and impaired contractility, whereas PKM2 overexpression and activation mitigated SIC. Mechanism investigation revealed that PKM2 interacted with sarcoplasmic/endoplasmic reticulum calcium ATPase 2a (SERCA2a), a key regulator of the excitation-contraction coupling, to maintain calcium homeostasis, and PKM2 deficiency exacerbated LPS-induced cardiac systolic dysfunction by impairing SERCA2a expression. In conclusion, these findings highlight that PKM2 plays an essential role in gram-negative sepsis-induced cardiomyopathy, which provides an attractive target for the prevention and treatment of septic cardiomyopathy.

TMEM41B and VMP1 modulate cellular lipid and energy metabolism for facilitating dengue virus infection

Transmembrane Protein 41B (TMEM41B) and Vacuole Membrane Protein 1 (VMP1) are two ER-associated lipid scramblases that play a role in autophagosome formation and cellular lipid metabolism. TMEM41B is also a recently validated host factor required by flaviviruses and coronaviruses. However, the exact underlying mechanism of TMEM41B in promoting viral infections remains an open question. Here, we validated that both TMEM41B and VMP1 are essential host dependency factors for all four serotypes of dengue virus (DENV) and human coronavirus OC43 (HCoV-OC43), but not chikungunya virus (CHIKV). While HCoV-OC43 failed to replicate entirely in both TMEM41B- and VMP1-deficient cells, we detected diminished levels of DENV infections in these cell lines, which were accompanied by upregulation of the innate immune dsRNA sensors, RIG-I and MDA5. Nonetheless, this upregulation did not correspondingly induce the downstream effector TBK1 activation and Interferon-beta expression. Despite low levels of DENV replication, classical DENV replication organelles were undetectable in the infected TMEM41B-deficient cells, suggesting that the upregulation of the dsRNA sensors is likely a consequence of aberrant viral replication rather than a causal factor for reduced DENV infection. Intriguingly, we uncovered that the inhibitory effect of TMEM41B deficiency on DENV replication, but not HCoV-OC43, can be partially reversed using exogenous fatty acid supplements. In contrast, VMP1 deficiency cannot be rescued using the metabolite treatment. In line with the observed phenotypes, we found that both TMEM41B- and VMP1-deficient cells harbor higher levels of compromised mitochondria, especially in VMP1 deficiency which results in severe dysregulations of mitochondrial beta-oxidation. Using a metabolomic profiling approach, we revealed distinctive global dysregulations of the cellular metabolome, particularly lipidome, in TMEM41B- and VMP1-deficient cells. Our findings highlight a central role for TMEM41B and VMP1 in modulating multiple cellular pathways, including lipid mobilization, mitochondrial beta-oxidation, and global metabolic regulations, to facilitate the replication of flaviviruses and coronaviruses.

Given the concerns over potential global health burdens imposed by endless emerging and re-emerging viruses as well as the limited therapeutic options to intervene, host-directed therapeutics can serve as a promising approach to broadly prepare for future pandemics. TMEM41B and VMP1 have been demonstrated as essential host factors for at least two unrelated groups of clinically important RNA viruses with outbreak potential. Therefore these ER membrane proteins could potentially serve as cellular targets for developing host-directed therapeutics. However, the effort must be first supported by a comprehensive understanding of their function in viral infection. Here, we dissected the role of TMEM41B and VMP1 in dengue virus infection, showing that both these proteins are crucial for the normal functionality of mitochondria and the regulation of cellular metabolites. We further provided evidence that these metabolic roles contribute to TMEM41B and VMP1 essentiality in dengue virus infection.

Odd one out? Functional tuning of Zymomonas mobilis pyruvate kinase is narrower than its allosteric, human counterpart

Various protein properties are often illuminated using sequence comparisons of protein homologs. For example, in analyses of the pyruvate kinase multiple sequence alignment, the set of positions that changed during speciation ("phylogenetic" positions) were enriched for "rheostat" positions in human liver pyruvate kinase (hLPYK). (Rheostat positions are those which, when substituted with various amino acids, yield a range of functional outcomes). However, the correlation was moderate, which could result from multiple biophysical constraints acting on the same position during evolution and/or various sources of noise. To further examine this correlation, we here tested Zymomonas mobilis PYK (ZmPYK), which has <65% sequence identity to any other PYK sequence. Twenty-six ZmPYK positions were selected based on their phylogenetic scores, substituted with multiple amino acids, and assessed for changes in Kapp-PEP . Although we expected to identify multiple, strong rheostat positions, only one moderate rheostat position was detected. Instead, nearly half of the 271 ZmPYK variants were inactive and most others showed near wild-type function. Indeed, for the active ZmPYK variants, the total range of Kapp,PEP values ("tunability") was 40-fold less than that observed for hLPYK variants. The combined functional studies and sequence comparisons suggest that ZmPYK has evolved functional and/or structural attributes that differ from the rest of the family. We hypothesize that including such "orphan" sequences in MSA analyses obscures the correlations used to predict rheostat positions. Finally, results raise the intriguing biophysical question as to how the same protein fold can support rheostat positions in one homolog but not another.

Catalyst-Based Biomolecular Logic Gates

Regulatory processes in biology can be re-conceptualized in terms of logic gates, analogous to those in computer science. Frequently, biological systems need to respond to multiple, sometimes conflicting, inputs to provide the correct output. The language of logic gates can then be used to model complex signal transduction and metabolic processes. Advances in synthetic biology in turn can be used to construct new logic gates, which find a variety of biotechnology applications including in the production of high value chemicals, biosensing, and drug delivery. In this review, we focus on advances in the construction of logic gates that take advantage of biological catalysts, including both protein-based and nucleic acid-based enzymes. These catalyst-based biomolecular logic gates can read a variety of molecular inputs and provide chemical, optical, and electrical outputs, allowing them to interface with other types of biomolecular logic gates or even extend to inorganic systems. Continued advances in molecular modeling and engineering will facilitate the construction of new logic gates, further expanding the utility of biomolecular computing.

Diethyl phthalate (DEP) perturbs nitrogen metabolism in Saccharomyces cerevisiae

Phthalates are ubiquitously used as plasticizers in various consumer care products. Diethyl phthalate (DEP), one of the main phthalates, elicits developmental and reproductive toxicities but the underlying mechanisms are not fully understood. Chemogenomic profiling of DEP in S. cerevisiae revealed that two transcription factors Stp1 and Dal81 involved in the Ssy1-Ptr5-Ssy5 (SPS) amino acid-sensing pathway provide resistance to DEP. Growth inhibition of yeast cells by DEP was stronger in poor nitrogen medium in comparison to nitrogen-rich medium. Addition of amino acids to nitrogen-poor medium suppressed DEP toxicity. Catabolism of amino acids via the Ehrlich pathway is required for suppressing DEP toxicity. Targeted metabolite analyses showed that DEP treatment alters the amino acid profile of yeast cells. We propose that DEP inhibits the growth of yeast cells by affecting nitrogen metabolism and discuss the implications of our findings on DEP-mediated toxic effects in humans.

Pyruvate Kinase M2 Protects Heart from Pressure Overload-Induced Heart Failure by Phosphorylating RAC1

Background

Heart failure, caused by sustained pressure overload, remains a major public health problem. PKM (pyruvate kinase M) acts as a rate‐limiting enzyme of glycolysis. PKM2 (pyruvate kinase M2), an alternative splicing product of PKM, plays complex roles in various biological processes and diseases. However, the role of PKM2 in the development of heart failure remains unknown.

Methods and Results

Cardiomyocyte‐specific Pkm2 knockout mice were generated by crossing the floxed Pkm2 mice with α‐MHC (myosin heavy chain)‐Cre transgenic mice, and cardiac specific Pkm2 overexpression mice were established by injecting adeno‐associated virus serotype 9 system. The results showed that cardiomyocyte‐specific Pkm2 deletion resulted in significant deterioration of cardiac functions under pressure overload, whereas Pkm2 overexpression mitigated transverse aortic constriction‐induced cardiac hypertrophy and improved heart functions. Mechanistically, we demonstrated that PKM2 acted as a protein kinase rather than a pyruvate kinase, which inhibited the activation of RAC1 (rho family, small GTP binding protein)‐MAPK (mitogen‐activated protein kinase) signaling pathway by phosphorylating RAC1 in the progress of heart failure. In addition, blockade of RAC1 through NSC23766, a specific RAC1 inhibitor, attenuated pathological cardiac remodeling in Pkm2 deficiency mice subjected to transverse aortic constriction.

Conclusions

This study revealed that PKM2 attenuated overload‐induced pathological cardiac hypertrophy and heart failure, which provides an attractive target for the prevention and treatment of cardiomyopathies.

The K+-Dependent and -Independent Pyruvate Kinases Acquire the Active Conformation by Different Mechanisms

Eukarya pyruvate kinases possess glutamate at position 117 (numbering of rabbit muscle enzyme), whereas bacteria have either glutamate or lysine. Those with E117 are K⁺-dependent, whereas those with K117 are K⁺-independent. In a phylogenetic tree, 80% of the sequences with E117 are occupied by T113/K114/T120 and 77% of those with K117 possess L113/Q114/(L,I,V)120. This work aims to understand these residues’ contribution to the K⁺-independent pyruvate kinases using the K⁺-dependent rabbit muscle enzyme. Residues 117 and 120 are crucial in the differences between the K⁺-dependent and -independent mutants. K⁺-independent activity increased with L113 and Q114 to K117, but L120 induced structural differences that inactivated the enzyme. T120 appears to be key in folding the protein and closure of the lid of the active site to acquire its active conformation in the K⁺-dependent enzymes. E117K mutant was K⁺-independent and the enzyme acquired the active conformation by a different mechanism. In the K⁺-independent apoenzyme of Mycobacterium tuberculosis, K72 (K117) flips out of the active site; in the holoenzyme, K72 faces toward the active site bridging the substrates through water molecules. The results provide evidence that two different mechanisms have evolved for the catalysis of this reaction.

High-Throughput CRISPR Screens To Dissect Macrophage-Shigella Interactions

Shigellosis causes most diarrheal deaths worldwide, particularly affecting children. Shigella invades and replicates in the epithelium of the large intestine, eliciting inflammation and tissue destruction. To understand how Shigella rewires macrophages prior to epithelium invasion, we performed genome-wide and focused secondary CRISPR knockout and CRISPR interference (CRISPRi) screens in Shigella flexneri-infected human monocytic THP-1 cells. Knockdown of the Toll-like receptor 1/2 signaling pathway significantly reduced proinflammatory cytokine and chemokine production, enhanced host cell survival, and controlled intracellular pathogen growth. Knockdown of the enzymatic component of the mitochondrial pyruvate dehydrogenase complex enhanced THP-1 cell survival. Small-molecule inhibitors blocking key components of these pathways had similar effects; these were validated with human monocyte-derived macrophages, which closely mimic the in vivo physiological state of macrophages postinfection. High-throughput CRISPR screens can elucidate how S. flexneri triggers inflammation and redirects host pyruvate catabolism for energy acquisition before killing macrophages, pointing to new shigellosis therapies.

Dysregulated metabolism underpins Zika-virus-infection-associated impairment in fetal development

Zika virus (ZIKV) is an Aedes-mosquito-borne flavivirus that causes debilitating congenital and developmental disorders. Improved understanding of ZIKV pathogenesis could assist efforts to fill the therapeutic and vaccine gap. We use several ZIKV strains, including a pair differing by a single phenylalanine-to-leucine substitution (M-F37L) in the membrane (M) protein, coupled with unbiased genomics to demarcate the border between attenuated and pathogenic infection. We identify infection-induced metabolic dysregulation as a minimal set of host alterations that differentiates attenuated from pathogenic ZIKV strains. Glycolytic rewiring results in impaired oxidative phosphorylation and mitochondrial dysfunction that trigger inflammation and apoptosis in pathogenic but not attenuated ZIKV strains. Critically, pyruvate supplementation prevents cell death, in vitro, and rescues fetal development in ZIKV-infected dams. Our findings thus demonstrate dysregulated metabolism as an underpinning of ZIKV pathogenicity and raise the potential of pyruvate supplementation in expectant women as a prophylaxis against congenital Zika syndrome.

Structure, Function and Regulation of a Second Pyruvate Kinase Isozyme in Pseudomonas aeruginosa

Pseudomonas aeruginosa (PA) depends on the Entner-Doudoroff pathway (EDP) for glycolysis. The main enzymatic regulator in the lower half of the EDP is pyruvate kinase. PA contains genes that encode two isoforms of pyruvate kinase, denoted PykAPA and PykFPA. In other well-characterized organisms containing two pyruvate kinase isoforms (such as Escherichia coli) each isozyme is differentially regulated. The structure, function and regulation of PykAPA has been previously characterized in detail, so in this work, we set out to assess the biochemical and structural properties of the PykFPA isozyme. We show that pykF PA expression is induced in the presence of the diureide, allantoin. In spite of their relatively low amino acid sequence identity, PykAPA and PykFPA display broadly comparable kinetic parameters, and are allosterically regulated by a very similar set of metabolites. However, the x-ray crystal structure of PykFPA revealed significant differences compared with PykAPA. Notably, although the main allosteric regulator binding-site of PykFPA was empty, the "ring loop" covering the site adopted a partially closed conformation. Site-directed mutation of the proline residues flanking the ring loop yielded apparent "locked on" and "locked off" allosteric activation phenotypes, depending on the residue mutated. Analysis of PykFPA inter-protomer interactions supports a model in which the conformational transition(s) accompanying allosteric activation involve re-orientation of the A and B domains of the enzyme and subsequent closure of the active site.

Identification of the antibacterial mechanism of cryptotanshinone on methicillin-resistant Staphylococcus aureus using bioinformatics analysis

Cryptotanshinone (CT) is an extract from the traditional Chinese medicine Salvia miltiorrhiza, which inhibits the growth of methicillin-resistant Staphylococcus aureus (MRSA) in vitro. This study aims to determine the antibacterial mechanisms of CT by integrating bioinformatics analysis and microbiology assay. The microarray data of GSE13203 was retrieved from the Gene Expression Omnibus (GEO) database to screen the differentially expressed genes (DEGs) of S. aureus strains that were treated with CT treatment. Gene ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were used to identify the potential target of CT. Data mining on the microarray dataset indicated that pyruvate kinase (PK) might be involved in the antimicrobial activities of CT. The minimum inhibition concentrations (MICs) of CT or vancomycin against the MRSA strain ATCC43300 and seven other clinical strains were determined using the broth dilution method. The effects of CT on the activity of PK were further measured. In vitro tests verified that CT inhibited the growth of an MRSA reference strain and seven other clinical strains. CT hampered the activity of the PK of ATCC43300 and five clinical MRSA strains. CT might hinder bacterial energy metabolism by inhibiting the activity of PK.

Induction of the glycolysis product methylglyoxal on trimethylamine lyase synthesis in the intestinal microbiota from mice fed with choline and dietary fiber

The present study investigated the induction of the glycolysis product methylglyoxal by trimethylamine (TMA) lyase synthesis in the intestinal microbiota and investigated the intervention mechanism of the effects of dietary fiber on methylglyoxal formation. Intestinal digesta samples, collected from the ceca of mice fed with choline-rich and fiber-supplemented diets, were incubated in an anaerobic environment at 37 °C and pH 7.0 with choline, glycine, and methylglyoxal as inductive factors. The differences between the gut microbiota and its metagenomic and metabonomics profiles were determined using 16S rRNA gene sequencing analysis. The results elucidated that the different dietary interventions could induce differences in the composition of the microbiota, gene expression profiles associated with glycine metabolism, and glycolysis. As compared to the gut microbiota of choline-diet fed mice, fiber supplementation effectively altered the composition of the microbiota and inhibited the genes involved in choline metabolism, glycine and methylglyoxal accumulation, and TMA lyase expression, and improved the methylglyoxal utilization by regulating the pathway related to pyruvate production. However, the intervention of exogenous methylglyoxal significantly decreased these effects. These findings successfully revealed the correlations between the TMA lyase expression and glycine level, as well as the inhibitory effects of dietary fiber on the glycine level, thereby highlighting the role of common glycolytic metabolites as a potential target for TMA production.

Beyond mitochondria: Alternative energy-producing pathways from all strata of life

It is well-established that mitochondria are the powerhouses of the cell, producing adenosine triphosphate (ATP), the universal energy currency. However, the most significant strengths of the electron transport chain (ETC), its intricacy and efficiency, are also its greatest downfalls. A reliance on metal complexes (FeS clusters, hemes), lipid moities such as cardiolipin, and cofactors including alpha-lipoic acid and quinones render oxidative phosphorylation vulnerable to environmental toxins, intracellular reactive oxygen species (ROS) and fluctuations in diet. To that effect, it is of interest to note that temporal disruptions in ETC activity in most organisms are rarely fatal, and often a redundant number of failsafes are in place to permit continued ATP production when needed. Here, we highlight the metabolic reconfigurations discovered in organisms ranging from parasitic Entamoeba to bacteria such as pseudomonads and then complex eukaryotic systems that allow these species to adapt to and occasionally thrive in harsh environments. The overarching aim of this review is to demonstrate the plasticity of metabolic networks and recognize that in times of duress, life finds a way.

Inhibition of Pyruvate Kinase From Thermoanaerobacterium saccharolyticum by IMP Is Independent of the Extra-C Domain

The pyruvate kinase (PYK) isozyme from Thermoanaerobacterium saccharolyticum (TsPYK) has previously been used in metabolic engineering for improved ethanol production. This isozyme belongs to a subclass of PYK isozymes that include an extra C-domain. Like other isozymes that include this extra C-domain, we found that TsPYK is activated by AMP and ribose-5-phosphate (R5P). Our use of sugar-phosphate analogs generated a surprising result in that IMP and GMP are allosteric inhibitors (rather than activators) of TsPYK. We believe this to be the first report of any PYK isozyme being inhibited by IMP and GMP. A truncated protein that lacks the extra C-domain is also inhibited by IMP. A screen of several other bacterial PYK enzymes (include several that have the extra-C domain) indicates that the inhibition by IMP is specific to only a subset of those isozymes.

Bedaquiline reprograms central metabolism to reveal glycolytic vulnerability in Mycobacterium tuberculosis

The approval of bedaquiline (BDQ) for the treatment of tuberculosis has generated substantial interest in inhibiting energy metabolism as a therapeutic paradigm. However, it is not known precisely how BDQ triggers cell death in Mycobacterium tuberculosis (Mtb). Using ¹³C isotopomer analysis, we show that BDQ-treated Mtb redirects central carbon metabolism to induce a metabolically vulnerable state susceptible to genetic disruption of glycolysis and gluconeogenesis. Metabolic flux profiles indicate that BDQ-treated Mtb is dependent on glycolysis for ATP production, operates a bifurcated TCA cycle by increasing flux through the glyoxylate shunt, and requires enzymes of the anaplerotic node and methylcitrate cycle. Targeting oxidative phosphorylation (OXPHOS) with BDQ and simultaneously inhibiting substrate level phosphorylation via genetic disruption of glycolysis leads to rapid sterilization. Our findings provide insight into the metabolic mechanism of BDQ-induced cell death and establish a paradigm for the development of combination therapies that target OXPHOS and glycolysis.

Structural and kinetic characterization of Trypanosoma congolense pyruvate kinase

Trypanosoma are blood-borne parasites and are the causative agents of neglected tropical diseases (NTDs) affecting both humans and animals. These parasites mainly rely on glycolysis for their energy production within the mammalian host, which is why trypanosomal glycolytic enzymes have been pursued as interesting targets for the development of trypanocidal drugs. The structure-function relationships of pyruvate kinases (PYKs) from trypanosomatids (Trypanosoma and Leishmania) have been well-studied within this context. In this paper, we describe the structural and enzymatic characterization of PYK from T. congolense (TcoPYK), the main causative agent of Animal African Trypanosomosis (AAT), by employing a combination of enzymatic assays, thermal unfolding studies and X-ray crystallography.

Integrated Computational Approaches and Tools forAllosteric Drug Discovery

Understanding molecular mechanisms underlying the complexity of allosteric regulationin proteins has attracted considerable attention in drug discovery due to the benefits and versatilityof allosteric modulators in providing desirable selectivity against protein targets while minimizingtoxicity and other side effects. The proliferation of novel computational approaches for predictingligand-protein interactions and binding using dynamic and network-centric perspectives has ledto new insights into allosteric mechanisms and facilitated computer-based discovery of allostericdrugs. Although no absolute method of experimental and in silico allosteric drug/site discoveryexists, current methods are still being improved. As such, the critical analysis and integration ofestablished approaches into robust, reproducible, and customizable computational pipelines withexperimental feedback could make allosteric drug discovery more efficient and reliable. In this article,we review computational approaches for allosteric drug discovery and discuss how these tools can beutilized to develop consensus workflows for in silico identification of allosteric sites and modulatorswith some applications to pathogen resistance and precision medicine. The emerging realization thatallosteric modulators can exploit distinct regulatory mechanisms and can provide access to targetedmodulation of protein activities could open opportunities for probing biological processes and insilico design of drug combinations with improved therapeutic indices and a broad range of activities.

A biocomputing platform with electrochemical and fluorescent signal outputs based on multi-sensitive copolymer film electrodes with entrapped Au nanoclusters and tetraphenylethene and electrocatalysis of NADH

In this work, poly(N,N'-dimethylaminoethylmethacrylate-co-N-isopropylacrylamide) copolymer films were polymerized on the surface of Au electrodes with a facile one-step method, and Au nanoclusters (AuNCs) and tetraphenylethene (TPE) were synchronously embedded in the films, designated as P(DMA-co-NIPA)/AuNCs/TPE. Ferrocene dicarboxylic acid (FDA), an electroactive probe in solution displayed inverse pH- and SO42--sensitive on-off cyclic voltammetric (CV) behaviors at the film electrodes. The electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) mediated by FDA in solution could substantially amplify the CV response difference between the on and off states. Moreover, the two fluorescence emission (FL) signals from the TPE constituent at 450 nm and AuNCs component at 660 nm in the films also demonstrated SO42-- and pH-sensitive behaviors. Based on the aforementioned results, a 4-input/9-output biomolecular logic circuit was constructed with pH, Na2SO4, FDA and NADH as the inputs, and the CV signals and the FL responses at 450 and 660 nm at different levels as the outputs. Additionally, some functional non-Boolean devices were elaborately designed on an identical platform, including a 1-to-2 decoder, a 2-to-1 encoder, a 1-to-2 demultiplexer and different types of keypad locks. This work combines copolymer films, bioelectrocatalysis, and fluorescence together so that more complicated biocomputing systems could be established. This work may pave a new way to develop advanced and sophisticated biocomputing logic circuits and functional devices in the future.

Biochemical and biophysical characterization of the smallest pyruvate kinase from Entamoeba histolytica

Entamoeba histolytica infection is highly prevalent in developing countries across the globe. The ATP synthesis in this pathogen is solely dependent on the glycolysis pathway where pyruvate kinase (Pyk) catalyzes the final reaction. Here, we have cloned, overexpressed and purified the pyruvate kinase (EhPyk) from E. histolytica. EhPyk is the shortest currently known Pyk till date as it contains only two of the three characterized domains when compared to the other homologues and our phylogenetic analysis places it on a distinct branch from the known type I/II Pyks. Our purification results suggested that it exists as a homodimer in solution. The kinetic characterization showed that EhPyk has maximum activity at pH 7.5 where it exhibited Michaelis-Menten's kinetics for phosphoenolpyruvate with a K_m of 0.23 mM, and it lost its activity at both the acidic pH 4.0 and basic pH 10.0. We also determined the key secondary structural elements of EhPyk at different pH values. MD simulation of EhPyk structure at different pH values suggested that it is most stable at pH 7.0, while least stable at pH 10.0 followed by pH 4.0. Together, our computational simulations correlate well with the experimental studies. In summary, this study expands the current understanding of the EhPyk identified earlier in the amoebic genome and provides the first characterization of this bacterially expressed protein.

Evolutionary plasticity in the allosteric regulator-binding site of pyruvate kinase isoform PykA from Pseudomonas aeruginosa

Unlike many other well-characterized bacteria, the opportunistic human pathogen Pseudomonas aeruginosa relies exclusively on the Entner-Doudoroff pathway (EDP) for glycolysis. Pyruvate kinase (PK) is the main "pacemaker" of the EDP, and its activity is also relevant for P. aeruginosa virulence. Two distinct isozymes of bacterial PK have been recognized, PykA and PykF. Here, using growth and expression analyses of relevant PK mutants, we show that PykA is the dominant isoform in P. aeruginosa Enzyme kinetics assays revealed that PykA displays potent K-type allosteric activation by glucose 6-phosphate and by intermediates from the pentose phosphate pathway. Unexpectedly, the X-ray structure of PykA at 2.4 Å resolution revealed that glucose 6-phosphate binds in a pocket that is distinct from the binding site reported for this metabolite in the PK from Mycobacterium tuberculosis (the only other available bacterial PK structure containing bound glucose 6-phosphate). We propose a mechanism by which glucose 6-phosphate binding at the allosteric site communicates with the PykA active site. Taken together, our findings indicate remarkable evolutionary plasticity in the mechanism(s) by which PK senses and responds to allosteric signals.

Metabolic principles of persistence and pathogenicity in Mycobacterium tuberculosis

Metabolism was once relegated to the supply of energy and biosynthetic precursors, but it has now become clear that it is a specific mediator of nearly all physiological processes. In the context of microbial pathogenesis, metabolism has expanded outside its canonical role in bacterial replication. Among human pathogens, this expansion has emerged perhaps nowhere more visibly than for Mycobacterium tuberculosis, the causative agent of tuberculosis. Unlike most pathogens, M. tuberculosis has evolved within humans, which are both host and reservoir. This makes unrestrained replication and perpetual quiescence equally incompatible strategies for survival as a species. In this Review, we summarize recent work that illustrates the diversity of metabolic functions that not only enable M. tuberculosis to establish and maintain a state of chronic infection within the host but also facilitate its survival in the face of drug pressure and, ultimately, completion of its life cycle.

An overview of structure, function, and regulation of pyruvate kinases

In the last step of glycolysis Pyruvate kinase catalyzes the irreversible conversion of ADP and phosphoenolpyruvate to ATP and pyruvic acid, both crucial for cellular metabolism. Thus pyruvate kinase plays a key role in controlling the metabolic flux and ATP production. The hallmark of the activity of different pyruvate kinases is their tight modulation by a variety of mechanisms including the use of a large number of physiological allosteric effectors in addition to their homotropic regulation by phosphoenolpyruvate. Binding of effectors signals precise and orchestrated movements in selected areas of the protein structure that alter the catalytic action of these evolutionarily conserved enzymes with remarkably conserved architecture and sequences. While the diverse nature of the allosteric effectors has been discussed in the literature, the structural basis of their regulatory effects is still not well understood because of the lack of data representing conformations in various activation states. Results of recent studies on pyruvate kinases of different families suggest that members of evolutionarily related families follow somewhat conserved allosteric strategies but evolutionarily distant members adopt different strategies. Here we review the structure and allosteric properties of pyruvate kinases of different families for which structural data are available.

Pyruvate Kinase Regulates the Pentose-Phosphate Pathway in Response to Hypoxia in Mycobacterium tuberculosis

In response to the stress of infection, Mycobacterium tuberculosis (Mtb) reprograms its metabolism to accommodate nutrient and energetic demands in a changing environment. Pyruvate kinase (PYK) is an essential glycolytic enzyme in the phosphoenolpyruvate-pyruvate-oxaloacetate node that is a central switch point for carbon flux distribution. Here we show that the competitive binding of pentose monophosphate inhibitors or the activator glucose 6-phosphate (G6P) to MtbPYK tightly regulates the metabolic flux. Intriguingly, pentose monophosphates were found to share the same binding site with G6P. The determination of a crystal structure of MtbPYK with bound ribose 5-phosphate (R5P), combined with biochemical analyses and molecular dynamic simulations, revealed that the allosteric inhibitor pentose monophosphate increases PYK structural dynamics, weakens the structural network communication, and impairs substrate binding. G6P, on the other hand, primes and activates the tetramer by decreasing protein flexibility and strengthening allosteric coupling. Therefore, we propose that MtbPYK uses these differences in conformational dynamics to up- and down-regulate enzymic activity. Importantly, metabolome profiling in mycobacteria reveals a significant increase in the levels of pentose monophosphate during hypoxia, which provides insights into how PYK uses dynamics of the tetramer as a competitive allosteric mechanism to retard glycolysis and facilitate metabolic reprogramming toward the pentose-phosphate pathway for achieving redox balance and an anticipatory metabolic response in Mtb.

Ligand-Binding-Site Structure Shapes Allosteric Signal Transduction and the Evolution of Allostery in Protein Complexes

The structure of ligand-binding sites has been shown to profoundly influence the evolution of function in homomeric protein complexes. Complexes with multichain binding sites (MBSs) have more conserved quaternary structure, more similar binding sites and ligands between homologs, and evolve new functions slower than homomers with single-chain binding sites (SBSs). Here, using in silico analyses of protein dynamics, we investigate whether ligand-binding-site structure shapes allosteric signal transduction pathways, and whether the structural similarity of binding sites influences the evolution of allostery. Our analyses show that: 1) allostery is more frequent among MBS complexes than in SBS complexes, particularly in homomers; 2) in MBS homomers, semirigid communities and critical residues frequently connect interfaces and thus they are characterized by signal transduction pathways that cross protein-protein interfaces, whereas SBS homomers usually not; 3) ligand binding alters community structure differently in MBS and SBS homomers; and 4) except MBS homomers, allosteric proteins are more likely to have homologs with similar binding site than nonallosteric proteins, suggesting that binding site similarity is an important factor driving the evolution of allostery.

Functional cross-talk between allosteric effects of activating and inhibiting ligands underlies PKM2 regulation

Several enzymes can simultaneously interact with multiple intracellular metabolites, however, how the allosteric effects of distinct ligands are integrated to coordinately control enzymatic activity remains poorly understood. We addressed this question using, as a model system, the glycolytic enzyme pyruvate kinase M2 (PKM2). We show that the PKM2 activator fructose 1,6-bisphosphate (FBP) alone promotes tetramerisation and increases PKM2 activity, but addition of the inhibitor L-phenylalanine (Phe) prevents maximal activation of FBP-bound PKM2 tetramers. We developed a method, AlloHubMat, that uses eigenvalue decomposition of mutual information derived from molecular dynamics trajectories to identify residues that mediate FBP-induced allostery. Experimental mutagenesis of these residues identified PKM2 variants in which activation by FBP remains intact but cannot be attenuated by Phe. Our findings reveal residues involved in FBP-induced allostery that enable the integration of allosteric input from Phe and provide a paradigm for the coordinate regulation of enzymatic activity by simultaneous allosteric inputs.

New views on an old enzyme: allosteric regulation and evolution of archaeal pyruvate kinases

Pyruvate kinases (PKs) synthesize ATP as the final step of glycolysis in the three domains of life. PKs from most bacteria and eukarya are allosteric enzymes that are activated by sugar phosphates; for example, the feed-forward regulator fructose-1,6-bisphosphate, or AMP as a sensor of energy charge. Archaea utilize unusual glycolytic pathways, but the allosteric properties of PKs from these species are largely unknown. Here, we present an analysis of 24 PKs from most archaeal clades with respect to allosteric properties, together with phylogenetic analyses constructed using a novel mode of rooting protein trees. We find that PKs from many Thermoproteales, an order of crenarchaeota, are allosterically activated by 3-phosphoglycerate (3PG). We also identify five conserved amino acids that form the binding pocket for 3PG. 3PG is generated via an irreversible reaction in the modified glycolytic pathway of these archaea and therefore functions as a feed-forward regulator. We also show that PKs from hyperthermophilic Methanococcales, an order of euryarchaeota, are activated by AMP. Phylogenetic analyses indicate that 3PG-activated PKs form an evolutionary lineage that is distinct from that of sugar-phosphate activated PKs, and that sugar phosphate-activated PKs originated as AMP-regulated PKs in hyperthermophilic Methanococcales. Since the phospho group of sugar phosphates and 3PG overlap in the allosteric site, our data indicate that the allostery in PKs first started from a progenitor phosphate-binding site that evolved in two spatially distinct directions: one direction generated the canonical site that responds to sugar phosphates and the other gave rise to the 3PG site present in Thermoproteales. Overall, our data suggest an intimate connection between the allosteric properties and evolution of PKs.

Allosteric regulation of pyruvate kinase from Mycobacterium tuberculosis by metabolites

Mycobacterium tuberculosis (Mtb) causes both acute tuberculosis and latent, symptom-free infection that affects roughly one-third of the world's population. It is a globally important pathogen that poses multiple dangers. Mtb reprograms its metabolism in response to the host niche, and this adaptation contributes to its pathogenicity. Knowledge of the metabolic regulation mechanisms in Mtb is still limited. Pyruvate kinase, involved in the late stage of glycolysis, helps link various metabolic routes together. Here, we demonstrate that Mtb pyruvate kinase (Mtb PYK) predominantly catalyzes the reaction leading to the production of pyruvate, but its activity is influenced by multiple metabolites from closely interlinked pathways that act as allosteric regulators (activators and inhibitors). We identified allosteric activators and inhibitors of Mtb PYK originating from glycolysis, citrate cycle, nucleotide/nucleoside inter-conversion related pathways that had not been described so far. Enzyme was found to be activated by fructose-1,6-bisphosphate, ribose-5-phosphate, adenine, adenosine, hypoxanthine, inosine, L-2-phosphoglycerate, l-aspartate, glycerol-2-phosphate, glycerol-3-phosphate. On the other hand thiamine pyrophosphate, glyceraldehyde-3-phosphate and L-malate were identified as inhibitors of Mtb PYK. The detailed kinetic analysis indicated a morpheein model of Mtb PYK allosteric control which is strictly dependent on Mg²⁺ and substantially increased by the co-presence of Mg²⁺ and K⁺.

Redox regulation of pyruvate kinase M2 by cysteine oxidation and S-nitrosation

We show here that the M2 isoform of human pyruvate kinase (M2PYK) is susceptible to nitrosation and oxidation, and that these modifications regulate enzyme activity by preventing the formation of the active tetrameric form. The biotin-switch assay carried out on M1 and M2 isoforms showed that M2PYK is sensitive to nitrosation and that Cys326 is highly susceptible to redox modification. Structural and enzymatic studies have been carried out on point mutants for three cysteine residues (Cys424, Cys358, and Cys326) to characterise their potential roles in redox regulation. Nine cysteines are conserved between M2PYK and M1PYK. Cys424 is the only cysteine unique to M2PYK. C424S, C424A, and C424L showed a moderate effect on enzyme activity with 80, 100, and 140% activity, respectively, compared with M2PYK. C358 had been previously identified from in vivo studies to be the favoured target for oxidation. Our characterised mutant showed that this mutation stabilises tetrameric M2PYK, suggesting that the in vivo resistance to oxidation for the Cys358Ser mutation is due to stabilisation of the tetrameric form of the enzyme. In contrast, the Cys326Ser mutant exists predominantly in monomeric form. A biotin-switch assay using this mutant also showed a significant reduction in biotinylation of M2PYK, confirming that this is a major target for nitrosation and probably oxidation. Our results show that the sensitivity of M2PYK to oxidation and nitrosation is regulated by its monomer–tetramer equilibrium. In the monomer state, residues (in particular C326) are exposed to oxidative modifications that prevent reformation of the active tetrameric form.