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

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.

Secreted PGK1 and IGFBP2 contribute to the bystander effect of miR-10b gene editing in glioma

MicroRNA-10b (miR-10b) is an essential glioma driver and one of the top candidates for targeted therapies for glioblastoma and other cancers. This unique miRNA controls glioma cell cycle and viability via an array of established conventional and unconventional mechanisms. Previously reported CRISPR-Cas9-mediated miR-10b gene editing of glioma cells in vitro and established orthotopic glioblastoma in mouse models demonstrated the efficacy of this approach and its promise for therapy development. However, therapeutic gene editing in patients' brain tumors may be hampered, among other factors, by the imperfect delivery and distribution of targeting vectors. Here, we demonstrate that miR-10b gene editing in glioma cells triggers a potent bystander effect that leads to the selective cell death of the unedited glioma cells without affecting the normal neuroglial cells. The effect is mediated by the secreted miR-10b targets phosphoglycerate kinase 1 (PGK1) and insulin-like growth factor binding protein 2 (IGFBP2) that block cell-cycle progression and induce glioma cell death. These findings further support the feasibility of therapeutic miR-10b editing without the need to target every cell of the tumor.

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.

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.

Dynamics of Substrate Processing by PPIP5K2, a Versatile Catalytic Machine

Processing of substrates by enzymes can only be fully understood through their conformational dynamics; this is particularly true for the diphosphoinositol pentakisphosphate kinase PPIP5K2, an enzyme with critical roles in cell signaling and bioenergetic homeostasis. PPIP5K2 is remarkable for the reversible nature of its kinase activity, its unique ligand-stimulated ATPase activity, and the substrate traveling between two ligand-binding sites. Here we use molecular dynamics and data analysis techniques to rationalize these PPIP5K2 activities, thereby increasing our understanding of complex enzymatic mechanisms. In particular, we demonstrate how the enzyme's distinctive, ratchet-like mechanism harnesses the energy of random fluctuations to significantly reduce the entropy toll for intramolecular substrate transfer. We show that pre-reaction pulling forces along the reaction coordinate are predictive of the various PPIP5K2 catalytic activities. An unexpected possibility, raised by these computational studies, that 3,5-IP8 might be a substrate for dephosphorylation was experimentally interrogated and confirmed in a luciferase assay.

Identification of potential allosteric communication pathways between functional sites of the bacterial ribosome by graph and elastic network models

BACKGROUND

Accumulated evidence indicates that bacterial ribosome employs allostery throughout its structure for protein synthesis. The nature of the allosteric communication between remote functional sites remains unclear, but the contact topology and dynamics of residues may play role in transmission of a perturbation to distant sites.

METHODS/RESULTS

We employ two computationally efficient approaches - graph and elastic network modeling to gain insights about the allosteric communication in ribosome. Using graph representation of the structure, we perform k-shortest pathways analysis between peptidyl transferase center-ribosomal tunnel, decoding center-peptidyl transferase center - previously reported functional sites having allosteric communication. Detailed analysis on intact structures points to common and alternative shortest pathways preferred by different states of translation. All shortest pathways capture drug target sites and allosterically important regions. Elastic network model further reveals that residues along all pathways have the ability of quickly establishing pair-wise communication and to help the propagation of a perturbation in long-ranges during functional motions of the complex.

CONCLUSIONS

Contact topology and inherent dynamics of ribosome configure potential communication pathways between functional sites in different translation states. Inter-subunit bridges B2a, B3 and P-tRNA come forward for their high potential in assisting allostery during translation. Especially B3 emerges as a potential druggable site.

GENERAL SIGNIFICANCE

This study indicates that the ribosome topology forms a basis for allosteric communication, which can be disrupted by novel drugs to kill drug-resistant bacteria. Our computationally efficient approach not only overlaps with experimental evidence on allosteric regulation in ribosome but also proposes new druggable sites.

Molecular Mechanism of Nucleotide-Dependent Allosteric Regulation in AMP-Activated Protein Kinase

The AMP-activated protein kinase (AMPK), a central enzyme in the regulation of energy homeostasis, is an important drug target for type 2 diabetes, obesity, and cancer. Binding of adenosine nucleotides to the regulatory γ-subunit tightly regulates the activity of this enzyme. Though recent crystal structures of AMPK have provided important insights into the allosteric activation of AMPK, molecular details of the regulatory mechanism of AMPK activation is still elusive. Here, we have performed extensive all-atom molecular dynamics (MD) simulations and shown that the kinase domain (KD) and γ-subunit come closer resulting in a more compact heterotrimeric AMPK complex in AMP-bound state compared to the ATP-bound state. The binding of ATP at site 3 of regulatory γ-subunit allosterically inhibits AMPK by destabilizing different regulatory regions of α-subunit: the autoinhibitory domain, the linker region, and the activation loop of the kinase core. The catalytically important residues experience a change in mechanical stress, and major rearrangements in community structure derived from residue-residue interaction energy-based network are observed in KD and α-linker region upon binding of different nucleotides. Our results also highlight the role of conserved charged residues forming an ionic network near the site 3 of γ-subunit in allosteric communications.

One-Way Allosteric Communication between the Two Disulfide Bonds in Tissue Factor

Tissue factor (TF) is a transmembrane glycoprotein that plays distinct roles in the initiation of extrinsic coagulation cascade and thrombosis. TF contains two disulfide bonds, one each in the N-terminal and C-terminal extracellular domains. The C-domain disulfide, Cys186-Cys209, has a -RHStaple configuration in crystal structures, suggesting that this disulfide carries high pre-stress. The redox state of this disulfide has been proposed to regulate TF encryption/decryption. Ablating the N-domain Cys49-Cys57 disulfide bond was found to increase the redox potential of the Cys186-Cys209 bond, implying an allosteric communication between the domains. Using molecular dynamics simulations, we observed that the Cys186-Cys209 disulfide bond retained the -RHStaple configuration, whereas the Cys49-Cys57 disulfide bond fluctuated widely. The Cys186-Cys209 bond featured the typical -RHStaple disulfide properties, such as a longer S-S bond length, larger C-S-S angles, and higher bonded prestress, in comparison to the Cys49-Cys57 bond. Force distribution analysis was used to sense the subtle structural changes upon ablating the disulfide bonds, and allowed us to identify a one-way allosteric communication mechanism from the N-terminal to the C-terminal domain. We propose a force propagation pathway using a shortest-pathway algorithm, which we suggest is a useful method for searching allosteric signal transduction pathways in proteins. As a possible explanation for the pathway being one-way, we identified a pronounced lower degree of conformational fluctuation, or effectively higher stiffness, in the N-terminal domain. Thus, the changes of the rigid domain (N-terminal domain) can induce mechanical force propagation to the soft domain (C-terminal domain), but not vice versa.

Advances in Quantum Mechanochemistry: Electronic Structure Methods and Force Analysis

In quantum mechanochemistry, quantum chemical methods are used to describe molecules under the influence of an external force. The calculation of geometries, energies, transition states, reaction rates, and spectroscopic properties of molecules on the force-modified potential energy surfaces is the key to gain an in-depth understanding of mechanochemical processes at the molecular level. In this review, we present recent advances in the field of quantum mechanochemistry and introduce the quantum chemical methods used to calculate the properties of molecules under an external force. We place special emphasis on quantum chemical force analysis tools, which can be used to identify the mechanochemically relevant degrees of freedom in a deformed molecule, and spotlight selected applications of quantum mechanochemical methods to point out their synergistic relationship with experiments.

Release of Entropic Spring Reveals Conformational Coupling Mechanism in the ABC Transporter BtuCD-F

Substrate translocation by ATP-binding cassette (ABC) transporters involves coupling of ATP binding and hydrolysis in the nucleotide-binding domains (NBDs) to conformational changes in the transmembrane domains. We used molecular dynamics simulations to investigate the atomic-level mechanism of conformational coupling in the ABC transporter BtuCD-F, which imports vitamin B12 across the inner membrane of Escherichia coli. Our simulations show how an engineered disulfide bond across the NBD dimer interface reduces conformational fluctuations and hence configurational entropy. As a result, the disulfide bond is under substantial mechanical stress. Releasing this entropic spring, as is the case in the wild-type transporter, combined with analyzing the pairwise forces between individual residues, unravels the coupling mechanism. The identified pathways along which force is propagated from the NBDs via the coupling helix to the transmembrane domains are composed of highly conserved residues, underlining their functional relevance. This study not only reveals the details of conformational coupling in BtuCD-F, it also provides a promising approach to other long-range conformational couplings, e.g., in ABC exporters or other ATP-driven molecular machines.

Dual Role of the Active Site Residues of Thermus thermophilus 3-Isopropylmalate Dehydrogenase: Chemical Catalysis and Domain Closure

The key active site residues K185, Y139, D217, D241, D245, and N102 of Thermus thermophilus 3-isopropylmalate dehydrogenase (Tt-IPMDH) have been replaced, one by one, with Ala. A drastic decrease in the kcat value (0.06% compared to that of the wild-type enzyme) has been observed for the K185A and D241A mutants. Similarly, the catalytic interactions (Km values) of these two mutants with the substrate IPM are weakened by more than 1 order of magnitude. The other mutants retained some (1-13%) of the catalytic activity of the wild-type enzyme and do not exhibit appreciable changes in the substrate Km values. The pH dependence of the wild-type enzyme activity (pK = 7.4) is shifted toward higher values for mutants K185A and D241A (pK values of 8.4 and 8.5, respectively). For the other mutants, smaller changes have been observed. Consequently, K185 and D241 may constitute a proton relay system that can assist in the abstraction of a proton from the OH group of IPM during catalysis. Molecular dynamics simulations provide strong support for the neutral character of K185 in the resting state of the enzyme, which implies that K185 abstracts the proton from the substrate and D241 assists the process via electrostatic interactions with K185. Quantum mechanics/molecular mechanics calculations revealed a significant increase in the activation energy of the hydride transfer of the redox step for both D217A and D241A mutants. Crystal structure analysis of the molecular contacts of the investigated residues in the enzyme-substrate complex revealed their additional importance (in particular that of K185, D217, and D241) in stabilizing the domain-closed active conformation. In accordance with this, small-angle X-ray scattering measurements indicated the complete absence of domain closure in the cases of D217A and D241A mutants, while only partial domain closure could be detected for the other mutants. This suggests that the same residues that are important for catalysis are also essential for inducing domain closure.

Mapping Mechanical Force Propagation through Biomolecular Complexes

Here we employ single-molecule force spectroscopy with an atomic force microscope (AFM) and steered molecular dynamics (SMD) simulations to reveal force propagation pathways through a mechanically ultrastable multidomain cellulosome protein complex. We demonstrate a new combination of network-based correlation analysis supported by AFM directional pulling experiments, which allowed us to visualize stiff paths through the protein complex along which force is transmitted. The results implicate specific force-propagation routes nonparallel to the pulling axis that are advantageous for achieving high dissociation forces.

Dynamic Allostery of the Catabolite Activator Protein Revealed by Interatomic Forces

The Catabolite Activator Protein (CAP) is a showcase example for entropic allostery. For full activation and DNA binding, the homodimeric protein requires the binding of two cyclic AMP (cAMP) molecules in an anti-cooperative manner, the source of which appears to be largely of entropic nature according to previous experimental studies. We here study at atomic detail the allosteric regulation of CAP with Molecular dynamics (MD) simulations. We recover the experimentally observed entropic penalty for the second cAMP binding event with our recently developed force covariance entropy estimator and reveal allosteric communication pathways with Force Distribution Analyses (FDA). Our observations show that CAP binding results in characteristic changes in the interaction pathways connecting the two cAMP allosteric binding sites with each other, as well as with the DNA binding domains. We identified crucial relays in the mostly symmetric allosteric activation network, and suggest point mutants to test this mechanism. Our study suggests inter-residue forces, as opposed to coordinates, as a highly sensitive measure for structural adaptations that, even though minute, can very effectively propagate allosteric signals.

The Catabolite Activator Protein (CAP) is a well-studied example for how cellular catabolite levels are integrated into the gene regulation. Its affinity for a specific stretch of DNA can be switched on by the binding of two nucleotide molecules termed cAMP to its two protomers. Even though the nucleotides occupy structurally identical binding pockets, the second cAMP binding occurs at an affinity orders of magnitude lower than the first cAMP binding. The question arises how, in the absence of structural changes, the first binding can affect the second. An answer from experiments has been that the communication is largely of entropic nature, i.e. the second cAMP binding would lead to a pronounced reduction in atomic fluctuations of the protein without affecting the atomic mean positions. We here revisited this question by performing Molecular Dynamics simulations. By measuring correlations of forces, a newly derived method outperforming the more common coordinate-based approach, we could recover the previously determined entropic penalty. In addition, however, we observed unobtrusive structural changes of side-chain interactions leading to the occlusion of the second binding pocket that add a critical ‘enthalpic’ component hitherto overlooked. Our study provides a mechanistic view onto the intriguing anti-cooperativity of CAP.

Allosteric regulation of focal adhesion kinase by PIP₂ and ATP

Focal adhesion kinase (FAK) is a nonreceptor tyrosine kinase that regulates cell signaling, proliferation, migration, and development. A major mechanism of regulation of FAK activity is an intramolecular autoinhibitory interaction between two of its domains--the catalytic and FERM domains. Upon cell adhesion to the extracellular matrix, FAK is being translocated toward focal adhesion sites and activated. Interactions of FAK with phosphoinositide phosphatidylinsositol-4,5-bis-phosphate (PIP₂) are required to activate FAK. However, the molecular mechanism of the activation remains poorly understood. Recent fluorescence resonance energy transfer experiments revealed a closure of the FERM-kinase interface upon ATP binding, which is reversed upon additional binding of PIP₂. Here, we addressed the allosteric regulation of FAK by performing all-atom molecular-dynamics simulations of a FAK fragment containing the catalytic and FERM domains, and comparing the dynamics in the absence or presence of ATP and PIP₂. As a major conformational change, we observe a closing and opening motion upon ATP and additional PIP₂ binding, respectively, in good agreement with the fluorescence resonance energy transfer experiments. To reveal how the binding of the regulatory PIP₂ to the FERM F2 lobe is transduced to the very distant F1/N-lobe interface, we employed force distribution analysis. We identified a network of mainly charged residue-residue interactions spanning from the PIP₂ binding site to the distant interface between the kinase and FERM domains, comprising candidate residues for mutagenesis to validate the predicted mechanism of FAK activation.

Calculation and visualization of atomistic mechanical stresses in nanomaterials and biomolecules

Many biomolecules have machine-like functions, and accordingly are discussed in terms of mechanical properties like force and motion. However, the concept of stress, a mechanical property that is of fundamental importance in the study of macroscopic mechanics, is not commonly applied in the biomolecular context. We anticipate that microscopical stress analyses of biomolecules and nanomaterials will provide useful mechanistic insights and help guide molecular design. To enable such applications, we have developed Calculator of Atomistic Mechanical Stress (CAMS), an open-source software package for computing atomic resolution stresses from molecular dynamics (MD) simulations. The software also enables decomposition of stress into contributions from bonded, nonbonded and Generalized Born potential terms. CAMS reads GROMACS topology and trajectory files, which are easily generated from AMBER files as well; and time-varying stresses may be animated and visualized in the VMD viewer. Here, we review relevant theory and present illustrative applications.

Allostery without a conformational change? Revisiting the paradigm

Classically, allostery induces a functional switch through a conformational change. However, lately an increasing number of studies concluded that the allostery they observe takes place through sheer dynamics. Here we explain that even if a structural comparison between the active and inactive states does not detect a conformational change, it does not mean that there is no conformational change. We list likely reasons for this lack of observation, including crystallization conditions and crystal effects; one of the states is disordered; the structural comparisons disregard the quaternary protein structure; overlooking synergy effects among allosteric effectors and graded incremental switches and too short molecular dynamics simulations. Specific functions are performed by distinct conformations; they emerge through specific interactions between conformationally selected states.