Transition state analogue structures of human phosphoglycerate kinase establish the importance of charge balance in catalysis

Phosphorylation of cytosolic hPGK1 affects protein stability and ligand binding: implications for its subcellular targeting in cancer

Human phosphoglycerate kinase 1(hPGK1) is a key glycolytic enzyme that regulates the balance between ADP and ATP concentrations inside the cell. Phosphorylation of hPGK1 at S203 and S256 has been associated with enzyme import from the cytosol to the mitochondria and the nucleus respectively. These changes in subcellular locations drive tumorigenesis and are likely associated with site-specific changes in protein stability. In this work, we investigate the effects of site-specific phosphorylation on thermal and kinetic stability and protein structural dynamics by hydrogen-deuterium exchange (HDX) and molecular dynamics (MD) simulations. We also investigate the binding of 3-phosphoglycerate and Mg-ADP using these approaches. We show that the phosphomimetic mutation S256D reduces hPGK1 kinetic stability by 50-fold, with no effect of the mutation S203D. Calorimetric studies of ligand binding show a large decrease in affinity for Mg-ADP in the S256D variant, whereas Mg-ADP binding to the WT and S203D can be accurately investigated using protein kinetic stability and binding thermodynamic models. HDX and MD simulations confirmed the destabilization caused by the mutation S256D (with some long-range effects on stability) and its reduced affinity for Mg-ADP due to the strong destabilization of its binding site (particularly in the apo-state). Our research provides evidence suggesting that modifications in protein stability could potentially enhance the translocation of hPGK1 to the nucleus in cancer. While the structural and energetic basis of its mitochondrial import remain unknown.

Magnesium induced structural reorganization in the active site of adenylate kinase

Phosphoryl transfer is a fundamental reaction in cellular signaling and metabolism that requires Mg2+ as an essential cofactor. While the primary function of Mg2+ is electrostatic activation of substrates, such as ATP, the full spectrum of catalytic mechanisms exerted by Mg2+ is not known. In this study, we integrate structural biology methods, molecular dynamic (MD) simulations, phylogeny, and enzymology assays to provide molecular insights into Mg2+-dependent structural reorganization in the active site of the metabolic enzyme adenylate kinase. Our results demonstrate that Mg2+ induces a conformational rearrangement of the substrates (ATP and ADP), resulting in a 30° adjustment of the angle essential for reversible phosphoryl transfer, thereby optimizing it for catalysis. MD simulations revealed transitions between conformational substates that link the fluctuation of the angle to large-scale enzyme dynamics. The findings contribute detailed insight into Mg2+ activation of enzymes and may be relevant for reversible and irreversible phosphoryl transfer reactions.

Metal fluorides-multi-functional tools for the study of phosphoryl transfer enzymes, a practical guide

Enzymes facilitating the transfer of phosphate groups constitute the most extensive protein families across all kingdoms of life. They make up approximately 10% of the proteins found in the human genome. Understanding the mechanisms by which enzymes catalyze these reactions is essential in characterizing the processes they regulate. Metal fluorides can be used as multifunctional tools to study these enzymes. These ionic species bear the same charge as phosphate and the transferring phosphoryl group and, in addition, allow the enzyme to be trapped in catalytically important states with spectroscopically sensitive atoms interacting directly with active site residues. The ionic nature of these phosphate surrogates also allows their removal and replacement with other analogs. Here, we describe the best practices to obtain these complexes, their use in NMR, X-ray crystallography, cryo-EM, and SAXS and describe a new metal fluoride, scandium tetrafluoride, which has significant anomalous signal using soft X-rays.

Chemoproteomic Profiling Maps Zinc-Dependent Cysteine Reactivity

As a vital micronutrient, zinc is integral to the structure, function, and signaling networks of diverse proteins. Dysregulated zinc levels, due to either excess intake or deficiency, are associated with a spectrum of health disorders. In this context, understanding zinc-regulated biological processes at the molecular level holds significant relevance to public health and clinical practice. Identifying and characterizing zinc-regulated proteins in their diverse proteoforms, however, remain a difficult task in advancing zinc biology. Herein, we address this challenge by developing a quantitative chemical proteomics platform that globally profiles the reactivities of proteinaceous cysteines upon cellular zinc depletion. Exploiting a protein-conjugated resin for the selective removal of Zn2+ from culture media, we identify an array of zinc-sensitive cysteines on proteins with diverse functions based on their increased reactivity upon zinc depletion. Notably, we find that zinc regulates the enzymatic activities, post-translational modifications, and subcellular distributions of selected target proteins such as peroxiredoxin 6 (PRDX6), platelet-activating factor acetylhydrolase IB subunit alpha1 (PAFAH1B3), and phosphoglycerate kinase (PGK1).

PRMT1-mediated PGK1 arginine methylation promotes colorectal cancer glycolysis and tumorigenesis

Many types of cancer cells, including colorectal cancer cells (CRC), can simultaneously enhance glycolysis and repress the mitochondrial tricarboxylic acid (TCA) cycle, which is called the Warburg effect. However, the detailed mechanisms of abnormal activation of the glycolysis pathway in colorectal cancer are largely unknown. In this study, we reveal that the protein arginine methyltransferase 1 (PRMT1) promotes glycolysis, proliferation, and tumorigenesis in CRC cells. Mechanistically, PRMT1-mediated arginine asymmetric dimethylation modification of phosphoglycerate kinase 1 (PGK1, the first ATP-producing enzyme in glycolysis) at R206 (meR206-PGK1) enhances the phosphorylation level of PGK1 at S203 (pS203-PGK1), which inhibits mitochondrial function and promotes glycolysis. We found that PRMT1 and meR206-PGK1 expression were positively correlated with pS203-PGK1 expression in tissues from colorectal cancer patients. Furthermore, we also confirmed that meR206-PGK1 expression is positively correlated with the poor survival of patients with colorectal cancer. Our findings show that PRMT1 and meR206-PGK1 may become promising predictive biomarkers for the prognosis of patients with CRC and that arginine methyltransferase inhibitors have great potential in colorectal cancer treatment.

Metastable States in the Hinge-Bending Landscape of an Enzyme in an Atomistic Cytoplasm Simulation

Many enzymes undergo major conformational changes to function in cells, particularly when they bind to more than one substrate. We quantify the large-amplitude hinge-bending landscape of human phosphoglycerate kinase (PGK) in a human cytoplasm. Approximately 70 μs of all-atom simulations, upon coarse graining, reveal three metastable states of PGK with different hinge angle distributions and additional substates. The "open" state was more populated than the "semi-open" or "closed" states. In addition to free energies and barriers within the landscape, we characterized the average transition state passage time of ≈0.3 μs and reversible substrate and product binding. Human PGK in a dilute solution simulation shows a transition directly from the open to closed states, in agreement with previous SAXS experiments, suggesting that the cell-like model environment promotes stability of the human PGK semi-open state. Yeast PGK also sampled three metastable states within the cytoplasm model, with the closed state favored in our simulation.

Far-reaching effects of tyrosine64 phosphorylation on Ras revealed with BeF3- complexes

Tyrosine phosphorylation on Ras by Src kinase is known to uncouple Ras from upstream regulation and downstream communication. However, the mechanisms by which phosphorylation modulates these interactions have not been detailed. Here, the major mono-phosphorylation level on tyrosine64 is quantified by 31P NMR and mutagenesis. Crystal structures of unphosphorylated and tyrosine64-phosphorylated Ras in complex with a BeF3- ground state analogue reveal "closed" Ras conformations very different from those of the "open" conformations previously observed for non-hydrolysable GTP analogue structures of Ras. They deliver new mechanistic and conformational insights into intrinsic GTP hydrolysis. Phosphorylation of tyrosine64 delivers conformational changes distant from the active site, showing why phosphorylated Ras has reduced affinity to its downstream effector Raf. 19F NMR provides evidence for changes in the intrinsic GTPase and nucleotide exchange rate and identifies the concurrent presence of a major "closed" conformation alongside a minor yet functionally important "open" conformation at the ground state of Ras. This study expands the application of metal fluoride complexes in revealing major and minor conformational changes of dynamic and modified Ras proteins.

Importance of aspartate 4 in the Mg2+ dependent regulation of Leishmania major PAS domain-containing phosphoglycerate kinase

Magnesium is an important divalent cation for the regulation of catalytic activity. Recently, we have described that the Mg2+ binding through the PAS domain inhibits the phosphoglycerate kinase (PGK) activity in PAS domain-containing PGK from Leishmania major (LmPAS-PGK) at neutral pH 7.5, but PGK activity is derepressed at acidic pH 5.5. The acidic residue within the PAS domain of LmPAS-PGK is expected to bind the cofactor Mg2+ ion at neutral pH, but which specific acidic residue(s) is/are responsible for the Mg2+ binding is still unknown. To identify the residues, we exploited mutational studies of all acidic (twelve Asp/Glu) residues in the PAS domain for plausible Mg2+ binding. Mg2+ ion-dependent repression at pH 7.5 is withdrawn by substitution of Asp-4 with Ala, whereas other acidic residue mutants (D16A, D22A, D24A, D29A, D43A, D44A, D60A, D63A, D77A, D87A, and E107A) showed similar features compared to the wild-type protein. Fluorescence spectroscopic studies and isothermal titration calorimetry analysis showed that the Asp-4 is crucial for Mg2+ binding in the absence of both PGK's substrates. These results suggest that Asp-4 residue in the regulatory (PAS) domain of wild type enzymes is required for Mg2+ dependent repressed state of the catalytic PGK domain at neutral pH.

Structural characterization of a novel cyclic 2,3-diphosphoglycerate synthetase involved in extremolyte production in the archaeon Methanothermus fervidus

The enzyme cyclic di-phosphoglycerate synthetase that is involved in the production of the osmolyte cyclic 2,3-diphosphoglycerate has been studied both biochemically and structurally. Cyclic 2,3-diphosphoglycerate is found exclusively in the hyperthermophilic archaeal methanogens, such as Methanothermus fervidus, Methanopyrus kandleri, and Methanothermobacter thermoautotrophicus. Its presence increases the thermostability of archaeal proteins and protects the DNA against oxidative damage caused by hydroxyl radicals. The cyclic 2,3-diphosphoglycerate synthetase enzyme has been crystallized and its structure solved to 1.7 Å resolution by experimental phasing. It has also been crystallized in complex with its substrate 2,3 diphosphoglycerate and the co-factor ADP and this structure has been solved to 2.2 Å resolution. The enzyme structure has two domains, the core domain shares some structural similarity with other NTP-dependent enzymes. A significant proportion of the structure, including a 127 amino acid N-terminal domain, has no structural similarity to other known enzyme structures. The structure of the complex shows a large conformational change that occurs in the enzyme during catalytic turnover. The reaction involves the transfer of the γ-phosphate group from ATP to the substrate 2,3 -diphosphoglycerate and the subsequent SN2 attack to form a phosphoanhydride. This results in the production of the unusual extremolyte cyclic 2,3 -diphosphoglycerate which has important industrial applications.

Synergistic effect of conformational changes in phosphoglycerate kinase 1 product release

In the glycolysis pathway, phosphoglycerate kinase 1 (PGK1) transfers one phosphoryl-group from 1,3-diphosphoglycerate (1,3BPG) to ADP to product 3-phosphoglycerate (3PG) and ATP. The catalytic process is accompanied with the conversion between the open conformation and the closed conformation of PGK1. However, the dynamic collaboration mechanism between the PGK1 conformation transition and the products releasing process remains poorly understood. Here using molecular dynamics simulations combined with molecular mechanics generalized born surface area (MM/GBSA) analysis, we demonstrated that PGK1 in the closed conformation first releases the product ATP to reach a semi-open conformation, and releases the product 3PG to achieve the full open conformation, which could accept new substrates ADP and 1,3BPG for the next cycle. It is noteworthy that the phosphorylation of PGK1 at T243 causes the loop region (residues L248-E260) flip outside the protein, and the phosphorylation of Y324 leads PGK1 become looser. Both modifications cause the exposure of the ADP/ATP binding site, which was beneficial for the substrates/products binding/releasing of PGK1. In addition, the other post translational modifications (PTMs) were also able to regulate the ligands binding/releasing with different effects. Our results revealed the dynamic cooperative molecular mechanism of PGK1 conformational transition with products releasing, as well as the influence of PTMs, which would contribute to the understanding of PGK1 substrates/products conversion process and the development of small molecule drugs targeting PGK1.Communicated by Ramaswamy H. Sarma.

Targeting phosphoglycerate kinases by tatridin A, a natural sesquiterpenoid endowed with anti-cancer activity, using a proteomic platform

Tatridin A (TatA) is a germacrane sesquiterpenoid containing one E-double bond and one Z-double bond in its 10-membered ring, which is fused to a 3-methylene-dihydrofuran-2-one moiety. Tatridin A bioactivity has been poorly investigated despite its interesting chemical structure. Here, a functional proteomic platform was adapted to disclose its most reliable targets in leukemia monocytic cells, and phosphoglycerate kinases were recognized as the most affine enzymes. Through a combination of limited proteolysis and molecular docking, it has been discovered that tatridin A interacts with the active domains of phosphoglycerate kinase 1, altering its hinge region, and it can be accountable for tatridin A inhibition potency on enzyme activity. A more detailed tatridin A biological profile showed that it is also fully active against gastric cancer cells, downregulating the mRNA levels of chemokine receptor 4 and β-catenin and inhibiting the invasiveness of living KATO III cells as a direct consequence of phosphoglycerate kinase 1 antagonism.

Sampling of Protein Conformational Space Using Hybrid Simulations: A Critical Assessment of Recent Methods

Recent years have seen several hybrid simulation methods for exploring the conformational space of proteins and their complexes or assemblies. These methods often combine fast analytical approaches with computationally expensive full atomic molecular dynamics (MD) simulations with the goal of rapidly sampling large and cooperative conformational changes at full atomic resolution. We present here a systematic comparison of the utility and limits of four such hybrid methods that have been introduced in recent years: MD with excited normal modes (MDeNM), collective modes-driven MD (CoMD), and elastic network model (ENM)-based generation, clustering, and relaxation of conformations (ClustENM) as well as its updated version integrated with MD simulations (ClustENMD). We analyzed the predicted conformational spaces using each of these four hybrid methods, applied to four well-studied proteins, triosephosphate isomerase (TIM), 3-phosphoglycerate kinase (PGK), HIV-1 protease (PR) and HIV-1 reverse transcriptase (RT), which provide extensive ensembles of experimental structures for benchmarking and comparing the methods. We show that a rigorous multi-faceted comparison and multiple metrics are necessary to properly assess the differences between conformational ensembles and provide an optimal protocol for achieving good agreement with experimental data. While all four hybrid methods perform well in general, being especially useful as computationally efficient methods that retain atomic resolution, the systematic analysis of the same systems by these four hybrid methods highlights the strengths and limitations of the methods and provides guidance for parameters and protocols to be adopted in future studies.

Molecular mechanism of glycolytic flux control intrinsic to human phosphoglycerate kinase

Glycolysis plays a fundamental role in energy production and metabolic homeostasis. The intracellular [adenosine triphosphate]/[adenosine diphosphate] ([ATP]/[ADP]) ratio controls glycolytic flux; however, the regulatory mechanism underlying reactions catalyzed by individual glycolytic enzymes enabling flux adaptation remains incompletely understood. Phosphoglycerate kinase (PGK) catalyzes the reversible phosphotransfer reaction, which directly produces ATP in a near-equilibrium step of glycolysis. Despite extensive studies on the transcriptional regulation of PGK expression, the mechanism in response to changes in the [ATP]/[ADP] ratio remains obscure. Here, we report a protein-level regulation of human PGK (hPGK) by utilizing the switching ligand-binding cooperativities between adenine nucleotides and 3-phosphoglycerate (3PG). This was revealed by nuclear magnetic resonance (NMR) spectroscopy at physiological salt concentrations. MgADP and 3PG bind to hPGK with negative cooperativity, whereas MgAMPPNP (a nonhydrolyzable ATP analog) and 3PG bind to hPGK with positive cooperativity. These opposite cooperativities enable a shift between different ligand-bound states depending on the intracellular [ATP]/[ADP] ratio. Based on these findings, we present an atomic-scale description of the reaction scheme for hPGK under physiological conditions. Our results indicate that hPGK intrinsically modulates its function via ligand-binding cooperativities that are finely tuned to respond to changes in the [ATP]/[ADP] ratio. The alteration of ligand-binding cooperativities could be one of the self-regulatory mechanisms for enzymes in bidirectional pathways, which enables rapid adaptation to changes in the intracellular environment.

Octahedral Trifluoromagnesate, an Anomalous Metal Fluoride Species, Stabilizes the Transition State in a Biological Motor

Isoelectronic metal fluoride transition state analogue (TSA) complexes, MgF₃^– and AlF₄^–, have proven to be immensely useful in understanding mechanisms of biological motors utilizing phosphoryl transfer. Here we report a previously unobserved octahedral TSA complex, MgF₃(H₂O)⁻, in a 1.5 Å resolution Zika virus NS3 helicase crystal structure. ¹⁹F NMR provided independent validation and also the direct observation of conformational tightening resulting from ssRNA binding in solution. The TSA stabilizes the two conformations of motif V of the helicase that link ATP hydrolysis with mechanical work. DFT analysis further validated the MgF₃(H₂O)⁻ species, indicating the significance of this TSA for studies of biological motors.

Phosphoglycerate kinase: structural aspects and functions, with special emphasis on the enzyme from Kinetoplastea

Phosphoglycerate kinase (PGK) is a glycolytic enzyme that is well conserved among the three domains of life. PGK is usually a monomeric enzyme of about 45 kDa that catalyses one of the two ATP-producing reactions in the glycolytic pathway, through the conversion of 1,3-bisphosphoglycerate (1,3BPGA) to 3-phosphoglycerate (3PGA). It also participates in gluconeogenesis, catalysing the opposite reaction to produce 1,3BPGA and ADP. Like most other glycolytic enzymes, PGK has also been catalogued as a moonlighting protein, due to its involvement in different functions not associated with energy metabolism, which include pathogenesis, interaction with nucleic acids, tumorigenesis progression, cell death and viral replication. In this review, we have highlighted the overall aspects of this enzyme, such as its structure, reaction kinetics, activity regulation and possible moonlighting functions in different protistan organisms, especially both free-living and parasitic Kinetoplastea. Our analysis of the genomes of different kinetoplastids revealed the presence of open-reading frames (ORFs) for multiple PGK isoforms in several species. Some of these ORFs code for unusually large PGKs. The products appear to contain additional structural domains fused to the PGK domain. A striking aspect is that some of these PGK isoforms are predicted to be catalytically inactive enzymes or ‘dead’ enzymes. The roles of PGKs in kinetoplastid parasites are analysed, and the apparent significance of the PGK gene duplication that gave rise to the different isoforms and their expression in Trypanosoma cruzi is discussed.

Allomorphy as a mechanism of post-translational control of enzyme activity

Enzyme regulation is vital for metabolic adaptability in living systems. Fine control of enzyme activity is often delivered through post-translational mechanisms, such as allostery or allokairy. β-phosphoglucomutase (βPGM) from Lactococcus lactis is a phosphoryl transfer enzyme required for complete catabolism of trehalose and maltose, through the isomerisation of β-glucose 1-phosphate to glucose 6-phosphate via β-glucose 1,6-bisphosphate. Surprisingly for a gatekeeper of glycolysis, no fine control mechanism of βPGM has yet been reported. Herein, we describe allomorphy, a post-translational control mechanism of enzyme activity. In βPGM, isomerisation of the K145-P146 peptide bond results in the population of two conformers that have different activities owing to repositioning of the K145 sidechain. In vivo phosphorylating agents, such as fructose 1,6-bisphosphate, generate phosphorylated forms of both conformers, leading to a lag phase in activity until the more active phosphorylated conformer dominates. In contrast, the reaction intermediate β-glucose 1,6-bisphosphate, whose concentration depends on the β-glucose 1-phosphate concentration, couples the conformational switch and the phosphorylation step, resulting in the rapid generation of the more active phosphorylated conformer. In enabling different behaviours for different allomorphic activators, allomorphy allows an organism to maximise its responsiveness to environmental changes while minimising the diversion of valuable metabolites.

β-phosphoglucomutase (βPGM) from Lactococcus lactis is a phosphoryl transfer enzyme required for catabolism of trehalose and maltose. Coupled analyses of multiple βPGM structures and enzymatic activity lead to the proposal of allomorphy — a post-translational mechanism controlling enzyme activity.

Potent Anticancer Effect of the Natural Steroidal Saponin Gracillin Is Produced by Inhibiting Glycolysis and Oxidative Phosphorylation-Mediated Bioenergetics

Metabolic rewiring to utilize aerobic glycolysis is a hallmark of cancer. However, recent findings suggest the role of mitochondria in energy generation in cancer cells and the metabolic switch to oxidative phosphorylation (OXPHOS) in response to the blockade of glycolysis. We previously demonstrated that the antitumor effect of gracillin occurs through the inhibition of mitochondrial complex II-mediated energy production. Here, we investigated the potential of gracillin as an anticancer agent targeting both glycolysis and OXPHOS in breast and lung cancer cells. Along with the reduction in adenosine triphosphate (ATP) production, gracillin markedly suppresses the production of several glycolysis-associated metabolites. A docking analysis and enzyme assay suggested phosphoglycerate kinase 1 (PGK1) is a potential target for the antiglycolytic effect of gracillin. Gracillin reduced the viability and colony formation ability of breast cancer cells by inducing apoptosis. Gracillin displayed efficacious antitumor effects in mice bearing breast cancer cell line or breast cancer patient-derived tumor xenografts with no overt changes in body weight. An analysis of publicly available datasets further suggested that PGK1 expression is associated with metastasis status and poor prognosis in patients with breast cancer. These results suggest that gracillin is a natural anticancer agent that inhibits both glycolysis and mitochondria-mediated bioenergetics.

Regulation of Leishmania major PAS domain-containing phosphoglycerate kinase by cofactor Mg2+ ion at neutral pH

Recently, we described the PAS domain-containing phosphoglycerate kinase (PGK) from Leishmania major (LmPAS-PGK) that shows acidic pH (5.5)-dependent optimum catalytic activity. The PAS domain of LmPAS-PGK is expected to regulate PGK activity during catalysis, but the mechanism of regulation by PAS domain at the molecular level is uncharacterized. In this work, we have utilized the full-length, PAS domain-deleted, and mutant enzymes to measure the enzymatic activity in the presence of divalent cation at various pH values. Catalytic activity measurement indicates that Mg²⁺ binding through PAS domain inhibits the PGK activity at pH 7.5, and this inhibition is withdrawn at pH 5.5. To identify the Mg²⁺ binding residues of the PAS domain, we exploited a systematic mutational analysis of all (four) His residues in the PAS domain for potential divalent cation binding. Replacement of His-57 with alanine resulted in depression in the presence of Mg²⁺ at pH 7.5, but H71A, H89A, and H111A showed similar characteristics with respect to the wild-type protein. Fluorescence and isothermal titration calorimetry studies revealed that H57 is responsible for Mg²⁺ binding in the absence of substrates. Thus, the protonated form of His57 at acidic pH 5.5 destabilizes the Mg²⁺ binding in the PAS domain, which is an essential requirement in the wild-type LmPAS-PGK for a conformational alteration in the sensor domain that, sequentially, activates the PGK domain, resulting in the synthesis of higher amounts of ATP.

The phosphoglycerate kinase 1 variants found in carcinoma cells display different catalytic activity and conformational stability compared to the native enzyme

Cancer cells are able to survive in difficult conditions, reprogramming their metabolism according to their requirements. Under hypoxic conditions they shift from oxidative phosphorylation to aerobic glycolysis, a behavior known as Warburg effect. In the last years, glycolytic enzymes have been identified as potential targets for alternative anticancer therapies. Recently, phosphoglycerate kinase 1 (PGK1), an ubiquitous enzyme expressed in all somatic cells that catalyzes the seventh step of glycolysis which consists of the reversible phosphotransfer reaction from 1,3-bisphosphoglycerate to ADP, has been discovered to be overexpressed in many cancer types. Moreover, several somatic variants of PGK1 have been identified in tumors. In this study we analyzed the effect of the single nucleotide variants found in cancer tissues on the PGK1 structure and function. Our results clearly show that the variants display a decreased catalytic efficiency and/or thermodynamic stability and an altered local tertiary structure, as shown by the solved X-ray structures. The changes in the catalytic properties and in the stability of the PGK1 variants, mainly due to the local changes evidenced by the X-ray structures, suggest also changes in the functional role of PGK to support the biosynthetic need of the growing and proliferating tumour cells.

1H, 15N, 13C backbone resonance assignments of human phosphoglycerate kinase in a transition state analogue complex with ADP, 3-phosphoglycerate and magnesium trifluoride

Human phosphoglycerate kinase (PGK) is an energy generating glycolytic enzyme that catalyses the transfer of a phosphoryl group from 1,3-bisphosphoglycerate (BPG) to ADP producing 3-phosphoglycerate (3PG) and ATP. PGK is composed of two α/β Rossmann-fold domains linked by a central α-helix and the active site is located in the cleft formed between the N-domain which binds BPG or 3PG, and the C-domain which binds the nucleotides ADP or ATP. Domain closure is required to bring the two substrates into close proximity for phosphoryl transfer to occur, however previous structural studies involving a range of native substrates and substrate analogues only yielded open or partly closed PGK complexes. X-ray crystallography using magnesium trifluoride (MgF₃^-) as a isoelectronic and near-isosteric mimic of the transferring phosphoryl group (PO₃^-), together with 3PG and ADP has been successful in trapping human PGK in a fully closed transition state analogue (TSA) complex. In this work we report the ¹H, ¹⁵N and ¹³C backbone resonance assignments of human PGK in the solution conformation of the fully closed PGK:3PG:MgF₃:ADP TSA complex. Assignments were obtained by heteronuclear multidimensional NMR spectroscopy. In total, 97% of all backbone resonances were assigned in the complex, with 385 out of a possible 399 residues assigned in the ¹H-¹⁵N TROSY spectrum. Prediction of solution secondary structure from a chemical shift analysis using the TALOS-N webserver is in good agreement with the published X-ray crystal structure of this complex.

Assessing the Influence of Mutation on GTPase Transition States by Using X-ray Crystallography, 19 F NMR, and DFT Approaches

We report X-ray crystallographic and ¹⁹ F NMR studies of the G-protein RhoA complexed with MgF₃^- , GDP, and RhoGAP, which has the mutation Arg85'Ala. When combined with DFT calculations, these data permit the identification of changes in transition state (TS) properties. The X-ray data show how Tyr34 maintains solvent exclusion and the core H-bond network in the active site by relocating to replace the missing Arg85' sidechain. The ¹⁹ F NMR data show deshielding effects that indicate the main function of Arg85' is electronic polarization of the transferring phosphoryl group, primarily mediated by H-bonding to O^3G and thence to P^G . DFT calculations identify electron-density redistribution and pinpoint why the TS for guanosine 5'-triphosphate (GTP) hydrolysis is higher in energy when RhoA is complexed with RhoGAP_Arg85'Ala relative to wild-type (WT) RhoGAP. This study demonstrates that ¹⁹ F NMR measurements, in combination with X-ray crystallography and DFT calculations, can reliably dissect the response of small GTPases to site-specific modifications.

Virtual Screening against Phosphoglycerate Kinase 1 in Quest of Novel Apoptosis Inhibitors

Inhibition of apoptosis is a potential therapy to treat human diseases such as neurodegenerative disorders (e.g., Parkinson’s disease), stroke, and sepsis. Due to the lack of druggable targets, it remains a major challenge to discover apoptosis inhibitors. The recent repositioning of a marketed drug (i.e., terazosin) as an anti-apoptotic agent uncovered a novel target (i.e., human phosphoglycerate kinase 1 (hPgk1)). In this study, we developed a virtual screening (VS) pipeline based on the X-ray structure of Pgk1/terazosin complex and applied it to a screening campaign for potential anti-apoptotic agents. The hierarchical filters in the pipeline (i.e., similarity search, a pharmacophore model, a shape-based model, and molecular docking) rendered 13 potential hits from Specs chemical library. By using PC12 cells (exposed to rotenone) as a cell model for bioassay, we first identified that AK-918/42829299, AN-465/41520984, and AT-051/43421517 were able to protect PC12 cells from rotenone-induced cell death. Molecular docking suggested these hit compounds were likely to bind to hPgk1 in a similar mode to terazosin. In summary, we not only present a versatile VS pipeline for potential apoptosis inhibitors discovery, but also provide three novel-scaffold hit compounds that are worthy of further development and biological study.

Metal Fluorides as Analogues for Studies on Phosphoryl Transfer Enzymes

The 1994 structure of a transition-state analogue with AlF₄^- and GDP complexed to G1α, a small G protein, heralded a new field of research into the structure and mechanism of enzymes that manipulate the transfer of phosphoryl (PO₃^- ) groups. The number of enzyme structures in the PDB containing metal fluorides (MF_x ) as ligands that imitate either a phosphoryl or a phosphate group was 357 at the end of 2016. They fall into three distinct geometrical classes: 1) Tetrahedral complexes based on BeF₃^- that mimic ground-state phosphates; 2) octahedral complexes, primarily based on AlF₄^- , which mimic "in-line" anionic transition states for phosphoryl transfer; and 3) trigonal bipyramidal complexes, represented by MgF₃^- and putative AlF₃⁰ moieties, which mimic the geometry of the transition state. The interpretation of these structures provides a deeper mechanistic understanding into the behavior and manipulation of phosphate monoesters in molecular biology. This Review provides a comprehensive overview of these structures, their uses, and their computational development.

Metal Fluorides: Tools for Structural and Computational Analysis of Phosphoryl Transfer Enzymes

The phosphoryl group, PO₃^-, is the dynamic structural unit in the biological chemistry of phosphorus. Its transfer from a donor to an acceptor atom, with oxygen much more prevalent than nitrogen, carbon, or sulfur, is at the core of a great majority of enzyme-catalyzed reactions involving phosphate esters, anhydrides, amidates, and phosphorothioates. The serendipitous discovery that the phosphoryl group could be labeled by "nuclear mutation," by substitution of PO₃^- by MgF₃^- or AlF₄^-, has underpinned the application of metal fluoride (MF _x ) complexes to mimic transition states for enzymatic phosphoryl transfer reactions, with sufficient stability for experimental analysis. Protein crystallography in the solid state and ¹⁹F NMR in solution have enabled direct observation of ternary and quaternary protein complexes embracing MF _x transition state models with precision. These studies have underpinned a radically new mechanistic approach to enzyme catalysis for a huge range of phosphoryl transfer processes, as varied as kinases, phosphatases, phosphomutases, and phosphohydrolases. The results, without exception, have endorsed trigonal bipyramidal geometry (tbp) for concerted, "in-line" stereochemistry of phosphoryl transfer. QM computations have established the validity of tbp MF _x complexes as reliable models for true transition states, delivering similar bond lengths, coordination to essential metal ions, and virtually identical hydrogen bond networks. The emergence of protein control of reactant orbital overlap between bond-forming species within enzyme transition states is a new challenging theme for wider exploration.

MgF3- and AlF4- transition state analogue complexes of yeast phosphoglycerate kinase

The phospho-transfer mechanism of yeast phosphoglycerate kinase (PGK) has been probed through formation of trifluoromagnesate (MgF₃^-) and tetrafluoroaluminate (AlF₄^-) transition state analogue complexes and analyzed using ¹⁹F, ¹H waterLOGSY and ¹H chemical shift perturbation NMR spectroscopy. We observed the first ¹⁹F NMR spectroscopic evidence for the formation of metal fluoride transition state analogues of yeast PGK and also observed significant changes to proton chemical shifts of PGK in the presence, but not in the absence, of fluoride upon titration of ligands, providing indirect evidence of the formation of a closed ternary transition state. WaterLOGSY NMR spectroscopy experiments using an uncompetitive model were used in an attempt to measure ligand binding affinities within the transition state analogue complexes.

(19)F NMR and DFT Analysis Reveal Structural and Electronic Transition State Features for RhoA-Catalyzed GTP Hydrolysis

Molecular details for RhoA/GAP catalysis of the hydrolysis of GTP to GDP are poorly understood. We use (19)F NMR chemical shifts in the MgF3(-) transition state analogue (TSA) complex as a spectroscopic reporter to indicate electron distribution for the γ-PO3(-) oxygens in the corresponding TS, implying that oxygen coordinated to Mg has the greatest electron density. This was validated by QM calculations giving a picture of the electronic properties of the transition state (TS) for nucleophilic attack of water on the γ-PO3(-) group based on the structure of a RhoA/GAP-GDP-MgF3(-) TSA complex. The TS model displays a network of 20 hydrogen bonds, including the GAP Arg85' side chain, but neither phosphate torsional strain nor general base catalysis is evident. The nucleophilic water occupies a reactive location different from that in multiple ground state complexes, arising from reorientation of the Gln-63 carboxamide by Arg85' to preclude direct hydrogen bonding from water to the target γ-PO3(-) group.

Synthesis, structure and reactivity of a terminal magnesium fluoride compound, [TpBut,Me]MgF: hydrogen bonding, halogen bonding and C-F bond formation

The bulky tris(3-tert-butyl-5-pyrazolyl)hydroborato ligand, [TpBut,Me], has been employed to obtain the first structurally characterized example of a molecular magnesium compound that features a terminal fluoride ligand, namely [TpBut,Me]MgF, via the reaction of [TpBut,Me]MgMe with Me3SnF. The chloride, bromide and iodide complexes, [TpBut,Me]MgX (X = Cl, Br, I), can also be obtained by an analogous method using Me3SnX. The molecular structures of the complete series of halide derivatives, [TpBut,Me]MgX (X = F, Cl, Br, I) have been determined by X-ray diffraction. In each case, the Mg-X bond lengths are shorter than the sum of the covalent radii, thereby indicating that there is a significant ionic component to the bonding, in agreement with density functional theory calculations. The fluoride ligand of [TpBut,Me]MgF undergoes halide exchange with Me3SiX (X = Cl, Br, I) to afford [TpBut,Me]MgX and Me3SiF. The other halide derivatives [TpBut,Me]MgX undergo similar exchange reactions, but the thermodynamic driving forces are much smaller than those involving fluoride transfer, a manifestation of the often discussed silaphilicity of fluorine. In accord with the highly polarized Mg-F bond, the fluoride ligand of [TpBut,Me]MgF is capable of serving as a hydrogen bond and halogen bond acceptor, such that it forms adducts with indole and C6F5I. [TpBut,Me]MgF also reacts with Ph3CCl to afford Ph3CF, thereby demonstrating that [TpBut,Me]MgF may be used to form C-F bonds.

Insulin and mTOR Pathway Regulate HDAC3-Mediated Deacetylation and Activation of PGK1

Phosphoglycerate kinase 1 (PGK1) catalyzes the reversible transfer of a phosphoryl group from 1, 3-bisphosphoglycerate (1, 3-BPG) to ADP, producing 3-phosphoglycerate (3-PG) and ATP. PGK1 plays a key role in coordinating glycolytic energy production with one-carbon metabolism, serine biosynthesis, and cellular redox regulation. Here, we report that PGK1 is acetylated at lysine 220 (K220), which inhibits PGK1 activity by disrupting the binding with its substrate, ADP. We have identified KAT9 and HDAC3 as the potential acetyltransferase and deacetylase, respectively, for PGK1. Insulin promotes K220 deacetylation to stimulate PGK1 activity. We show that the PI3K/AKT/mTOR pathway regulates HDAC3 S424 phosphorylation, which promotes HDAC3-PGK1 interaction and PGK1 K220 deacetylation. Our study uncovers a previously unknown mechanism for the insulin and mTOR pathway in regulation of glycolytic ATP production and cellular redox potential via HDAC3-mediated PGK1 deacetylation.

On the mechanism of phosphoenolpyruvate synthetase (PEPs) and its inhibition by sodium fluoride: potential magnesium and aluminum fluoride complexes of phosphoryl transfer

Phosphoenolpyruvate synthase (PEPs) catalyzes the conversion of pyruvate to phosphoenolpyruvate (PEP) using a two-step mechanism invoking a phosphorylated-His intermediate. Formation of PEP is an initial step in gluconeogenesis, and PEPs is essential for growth of Escherichia coli on 3-carbon sources such as pyruvate. The production of PEPs has also been linked to bacterial virulence and antibiotic resistance. As such, PEPs is of interest as a target for antibiotic development, and initial investigations of PEPs have indicated inhibition by sodium fluoride. Similar inhibition has been observed in a variety of phospho-transfer enzymes through the formation of metal fluoride complexes within the active site. Herein we quantify the inhibitory capacity of sodium fluoride through a coupled spectrophotometric assay. The observed inhibition provides indirect evidence for the formation of a MgF3−complex within the enzyme active site and insight into the phospho-transfer mechanism of PEPs. The effect of AlCl3on PEPs enzyme activity was also assessed and found to decrease substrate binding and turnover.

The energy landscape of adenylate kinase during catalysis

Kinases perform phosphoryl-transfer reactions in milliseconds; without enzymes, these reactions would take about 8,000 years under physiological conditions. Despite extensive studies, a comprehensive understanding of kinase energy landscapes, including both chemical and conformational steps, is lacking. Here we scrutinize the microscopic steps in the catalytic cycle of adenylate kinase, through a combination of NMR measurements during catalysis, pre-steady-state kinetics, molecular-dynamics simulations and crystallography of active complexes. We find that the Mg(2+) cofactor activates two distinct molecular events: phosphoryl transfer (>10(5)-fold) and lid opening (10(3)-fold). In contrast, mutation of an essential active site arginine decelerates phosphoryl transfer 10(3)-fold without substantially affecting lid opening. Our results highlight the importance of the entire energy landscape in catalysis and suggest that adenylate kinases have evolved to activate key processes simultaneously by precise placement of a single, charged and very abundant cofactor in a preorganized active site.

Polyphosphate-containing bisubstrate analogues as inhibitors of a bacterial cell wall thymidylyltransferase

The first synthesis and evaluation of bisubstrate analogues with a thymidylyltransferase is reported. WaterLOGSY NMR and kinetic analyses provide insight into bisubstrate analogue binding.

Insights into human phosphoglycerate kinase 1 deficiency as a conformational disease from biochemical, biophysical, and in vitro expression analyses

Mutations in genes encoding metabolic enzymes are often the cause of inherited diseases. Mutations usually affect the ability of proteins to fold properly, thus leading to enzyme loss of function. In this work, we explored the relationships between protein stability, aggregation, and degradation in vitro and inside cells in a large set of mutants associated with human phosphoglycerate kinase 1 (hPGK1) deficiency. To this end, we studied a third of the pathogenic alleles reported in the literature using expression analyses and biochemical, biophysical, and computational procedures. Our results show that most pathogenic variants studied had an increased tendency to aggregate when expressed in Escherichia coli, well correlating with the denaturation half-lives measured by thermal denaturation in vitro. Further, the most deleterious mutants show reduced stability toward chemical denaturation and proteolysis, supporting a pivotal role of thermodynamic stability in the propensity toward aggregation and proteolysis of pathogenic hPGK1 mutants in vitro and inside cells. Our strategy allowed us to unravel the complex relationships between protein stability, aggregation, and degradation in hPGK1 deficiency, which might be used to understand disease mechanisms in many inborn errors of metabolism. Our results suggest that pharmacological chaperones and protein homeostasis modulators could be considered as good candidates for therapeutic approaches for hPGK1 deficiency.

Thioredoxin-dependent redox regulation of chloroplastic phosphoglycerate kinase from Chlamydomonas reinhardtii

In photosynthetic organisms, thioredoxin-dependent redox regulation is a well established mechanism involved in the control of a large number of cellular processes, including the Calvin-Benson cycle. Indeed, 4 of 11 enzymes of this cycle are activated in the light through dithiol/disulfide interchanges controlled by chloroplastic thioredoxin. Recently, several proteomics-based approaches suggested that not only four but all enzymes of the Calvin-Benson cycle may withstand redox regulation. Here, we characterized the redox features of the Calvin-Benson enzyme phosphoglycerate kinase (PGK1) from the eukaryotic green alga Chlamydomonas reinhardtii, and we show that C. reinhardtii PGK1 (CrPGK1) activity is inhibited by the formation of a single regulatory disulfide bond with a low midpoint redox potential (-335 mV at pH 7.9). CrPGK1 oxidation was found to affect the turnover number without altering the affinity for substrates, whereas the enzyme activation appeared to be specifically controlled by f-type thioredoxin. Using a combination of site-directed mutagenesis, thiol titration, mass spectrometry analyses, and three-dimensional modeling, the regulatory disulfide bond was shown to involve the not strictly conserved Cys(227) and Cys(361). Based on molecular mechanics calculation, the formation of the disulfide is proposed to impose structural constraints in the C-terminal domain of the enzyme that may lower its catalytic efficiency. It is therefore concluded that CrPGK1 might constitute an additional light-modulated Calvin-Benson cycle enzyme with a low activity in the dark and a TRX-dependent activation in the light. These results are also discussed from an evolutionary point of view.

α-Fluorophosphonates reveal how a phosphomutase conserves transition state conformation over hexose recognition in its two-step reaction

β-Phosphoglucomutase (βPGM) catalyzes isomerization of β-D-glucose 1-phosphate (βG1P) into D-glucose 6-phosphate (G6P) via sequential phosphoryl transfer steps using a β-D-glucose 1,6-bisphosphate (βG16BP) intermediate. Synthetic fluoromethylenephosphonate and methylenephosphonate analogs of βG1P deliver novel step 1 transition state analog (TSA) complexes for βPGM, incorporating trifluoromagnesate and tetrafluoroaluminate surrogates of the phosphoryl group. Within an invariant protein conformation, the β-D-glucopyranose ring in the βG1P TSA complexes (step 1) is flipped over and shifted relative to the G6P TSA complexes (step 2). Its equatorial hydroxyl groups are hydrogen-bonded directly to the enzyme rather than indirectly via water molecules as in step 2. The (C)O-P bond orientation for binding the phosphate in the inert phosphate site differs by ∼ 30° between steps 1 and 2. By contrast, the orientations for the axial O-Mg-O alignment for the TSA of the phosphoryl group in the catalytic site differ by only ∼ 5°, and the atoms representing the five phosphorus-bonded oxygens in the two transition states (TSs) are virtually superimposable. The conformation of βG16BP in step 1 does not fit into the same invariant active site for step 2 by simple positional interchange of the phosphates: the TS alignment is achieved by conformational change of the hexose rather than the protein.

A structural perspective of compensatory evolution

The study of molecular evolution is important because it reveals how protein functions emerge and evolve. Recently, several types of studies indicated that substitutions in molecular evolution occur in a compensatory manner, whereby the occurrence of a substitution depends on the amino acid residues at other sites. However, a molecular or structural basis behind the compensation often remains obscure. Here, we review studies on the interface of structural biology and molecular evolution that revealed novel aspects of compensatory evolution. In many cases structural studies benefit from evolutionary data while structural data often add a functional dimension to the study of molecular evolution.

Phosphate analogues in the dissection of mechanism

Phosphoryl group transfer is central to genetic replication, cellular signalling and many metabolic processes. Understanding the mechanisms of phosphorylation and phosphate ester and anhydride cleavage is key to efforts towards biotechnological and biomedical exploitation of phosphate-handling enzymes. Analogues of phosphate esters and anhydrides are indispensable tools, alongside protein mutagenesis and computational methods, for the dissection of phosphoryl transfer mechanisms. Hydrolysable and non-hydrolysable phosphate analogues have provided insight into the nature and sites of phosphoryl transfer processes. Kinetic isotope effects and crystallography using transition state analogues have painted more detailed pictures of transition states and how enzymes work to stabilise them.

pH-dependent relationship between thermodynamic and kinetic stability in the denaturation of human phosphoglycerate kinase 1

Human phosphoglycerate kinase 1 (hPGK1) is a glycolytic enzyme essential for ATP synthesis, and it is implicated in different pathological conditions such as inherited diseases, oncogenesis and activation of drugs for cancer and viral treatments. Particularly, mutations in hPGK1 cause human PGK1 deficiency, a rate metabolic conformational disease. We have recently found that most of these mutations cause protein kinetic destabilization by significant changes in the structure/energetics of the transition state for irreversible denaturation. In this work, we explore the relationships between protein conformation, thermodynamic and kinetic stability in hPGK1 by performing comprehensive analyses in a wide pH range (2.5-8). hPGK1 remains in a native conformation at pH 5-8, but undergoes a conformational transition to a molten globule-like state at acidic pH. Interestingly, hPGK1 kinetic stability remains essentially constant at pH 6-8, but is significantly reduced when pH is decreased from 6 to 5. We found that this decrease in kinetic stability is caused by significant changes in the energetic/structural balance of the denaturation transition state, which diverge from those found for disease-causing mutations. We also show that protein kinetic destabilization by acidic pH is strongly linked to lower thermodynamic stability, while in disease-causing mutations seems to be linked to lower unfolding cooperativity. These results highlight the plasticity of the hPGK1 denaturation mechanism that responds differently to changes in pH and in disease-causing mutations. New insight is presented into the different factors contributing to hPGK1 thermodynamic and kinetic stability and the role of denaturation mechanisms in hPGK1 deficiency.

Crystal structures of the novel cytosolic 5'-nucleotidase IIIB explain its preference for m7GMP

5′-nucleotidases catalyze the hydrolytic dephosphorylation of nucleoside monophosphates. As catabolic enzymes they contribute significantly to the regulation of cellular nucleotide levels; misregulation of nucleotide metabolism and nucleotidase deficiencies are associated with a number of diseases. The seven human 5′-nucleotidases differ with respect to substrate specificity and cellular localization. Recently, the novel cytosolic 5′-nucleotidase III-like protein, or cN-IIIB, has been characterized in human and Drosophila. cN-IIIB exhibits a strong substrate preference for the modified nucleotide 7-methylguanosine monophosphate but the structural reason for this preference was unknown. Here, we present crystal structures of cN-IIIB from Drosophila melanogaster bound to the reaction products 7-methylguanosine or cytidine. The structural data reveal that the cytosine- and 7-methylguanine moieties of the products are stacked between two aromatic residues in a coplanar but off-centered position. 7-methylguanosine is specifically bound through π-π interactions and distinguished from unmodified guanosine by additional cation-π coulomb interactions between the aromatic side chains and the positively charged 7-methylguanine. Notably, the base is further stabilized by T-shaped edge-to-face stacking of an additional tryptophan packing perpendicularly against the purine ring and forming, together with the other aromates, an aromatic slot. The structural data in combination with site-directed mutagenesis experiments reveal the molecular basis for the broad substrate specificity of cN-IIIB but also explain the substrate preference for 7-methylguanosine monophosphate. Analyzing the substrate specificities of cN-IIIB and the main pyrimidine 5′-nucleotidase cN-IIIA by mutagenesis studies, we show that cN-IIIA dephosphorylates the purine m⁷GMP as well, hence redefining its substrate spectrum. Docking calculations with cN-IIIA and m⁷GMP as well as biochemical data reveal that Asn69 does not generally exclude the turnover of purine substrates thus correcting previous suggestions.

Theoretical studies of cyclic adenosine monophosphate dependent protein kinase: native enzyme and ground-state and transition-state analogues

The mechanisms of phosphoryl transfer enzymes have garnered considerable attention. Cyclic AMP-dependent protein kinase (cAPK) catalyzes the transfer of the γ phosphoryl group of ATP to the serine hydroxyl group of a peptide chain. Metal-containing fluoro species have been used as transition-state and ground-state analogues in a variety of phosphoryl transfer enzymes and have shed light on the nature of the requirements in the active site to catalyze phosphoryl transfer. For cAPK, we present computational studies of the mechanism of phosphoryl transfer and the structure and (19)F NMR spectra of various ground- (BeF3(-)) and transition-state (MgF3(-), AlF4(-), and AlF3(0)) analogues. With native substrate, the phosphoryl transfer proceeds through a five-coordinate phosphorane transition state, i.e., there is not a five-coordinate phosphorane intermediate. Comparisons of simulated and experimental (19)F NMR spectra show cAPK prefers a monoanionic analogue (MgF3(-) or AlF4(-)) over a neutral analogue (AlF3), supporting the charge balance hypothesis.

An allosteric signaling pathway of human 3-phosphoglycerate kinase from force distribution analysis

3-Phosphogycerate kinase (PGK) is a two domain enzyme, which transfers a phosphate group between its two substrates, 1,3-bisphosphoglycerate bound to the N-domain and ADP bound to the C-domain. Indispensable for the phosphoryl transfer reaction is a large conformational change from an inactive open to an active closed conformation via a hinge motion that should bring substrates into close proximity. The allosteric pathway resulting in the active closed conformation has only been partially uncovered. Using Molecular Dynamics simulations combined with Force Distribution Analysis (FDA), we describe an allosteric pathway, which connects the substrate binding sites to the interdomain hinge region. Glu192 of alpha-helix 7 and Gly394 of loop L14 act as hinge points, at which these two secondary structure elements straighten, thereby moving the substrate-binding domains towards each other. The long-range allosteric pathway regulating hPGK catalytic activity, which is partially validated and can be further tested by mutagenesis, highlights the virtue of monitoring internal forces to reveal signal propagation, even if only minor conformational distortions, such as helix bending, initiate the large functional rearrangement of the macromolecule.

3-Phosphoglycerate kinase (PGK) is an essential enzyme for living organisms. It catalyzes the phospho-transfer reaction between two catabolites during carbohydrate metabolism. In addition to this physiological role, human PGK has been shown to phosphorylate L-nucleoside analogues, potential drugs against viral infection and cancer. PGK is a two domain enzyme, with the two substrates bound to the two separate domains. In order to perform its function the enzyme has to undergo a large conformational change involving a hinge bending to bring the substrates into close proximity. The allosteric pathway from the open non-reactive state of PGK to the closed reactive state as triggered by substrate binding has only been partially uncovered by experimental studies. Here we describe a complete allosteric pathway, which connects the substrate binding sites to the interdomain hinge region using Molecular Dynamics simulations combined with Force Distribution Analysis (FDA). While previously identified key residues involved in PGK domain closure are part of this pathway, we here fill the numerous gaps in the pathway by identifying newly uncovered residues and interesting candidates for future mutational studies.

Measurement of the intrinsic variability within protein crystals: implications for sample-evaluation and data-collection strategies

The advent of micro-focused X-ray beams has led to the development of a number of advanced methods of sample evaluation and data collection. In particular, multiple-position data-collection and helical oscillation strategies are now becoming commonplace in order to alleviate the problems associated with radiation damage. However, intra-crystal and inter-crystal variation means that it is not always obvious on which crystals or on which region or regions of a crystal these protocols should be performed. For the automation of this process for large-scale screening, and to provide an indication of the best strategy for data collection, a metric of crystal variability could be useful. Here, measures of the intrinsic variability within protein crystals are presented and their implications for optimal data-collection strategies are discussed.

Protein Stability, Folding and Misfolding in Human PGK1 Deficiency

Conformational diseases are often caused by mutations, altering protein folding and stability in vivo. We review here our recent work on the effects of mutations on the human phosphoglycerate kinase 1 (hPGK1), with a particular focus on thermodynamics and kinetics of protein folding and misfolding. Expression analyses and in vitro biophysical studies indicate that disease-causing mutations enhance protein aggregation propensity. We found a strong correlation among protein aggregation propensity, thermodynamic stability, cooperativity and dynamics. Comparison of folding and unfolding properties with previous reports in PGKs from other species suggests that hPGK1 is very sensitive to mutations leading to enhance protein aggregation through changes in protein folding cooperativity and the structure of the relevant denaturation transition state for aggregation. Overall, we provide a mechanistic framework for protein misfolding of hPGK1, which is insightful to develop new therapeutic strategies aimed to target native state stability and foldability in hPGK1 deficient patients.

OptZyme: computational enzyme redesign using transition state analogues

OptZyme is a new computational procedure for designing improved enzymatic activity (i.e., kcat or kcat/KM) with a novel substrate. The key concept is to use transition state analogue compounds, which are known for many reactions, as proxies for the typically unknown transition state structures. Mutations that minimize the interaction energy of the enzyme with its transition state analogue, rather than with its substrate, are identified that lower the transition state formation energy barrier. Using Escherichia coli β-glucuronidase as a benchmark system, we confirm that KM correlates (R(2) = 0.960) with the computed interaction energy between the enzyme and the para-nitrophenyl- β, D-glucuronide substrate, kcat/KM correlates (R(2) = 0.864) with the interaction energy of the transition state analogue, 1,5-glucarolactone, and kcat correlates (R(2) = 0.854) with a weighted combination of interaction energies with the substrate and transition state analogue. OptZyme is subsequently used to identify mutants with improved KM, kcat, and kcat/KM for a new substrate, para-nitrophenyl- β, D-galactoside. Differences between the three libraries reveal structural differences that underpin improving KM, kcat, or kcat/KM. Mutants predicted to enhance the activity for para-nitrophenyl- β, D-galactoside directly or indirectly create hydrogen bonds with the altered sugar ring conformation or its substituents, namely H162S, L361G, W549R, and N550S.