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Epidermal growth factor receptor (EGFR) gene mutation is an important cause of non-small cell lung cancer (NSCLC) . The S768I point mutation is a rare mutation of EGFR, and there is no standard targeted therapy at present. Therefore, a detailed understanding of the structural differences between the EGFR S768I mutant and the wild type (WT) is crucial for the development of related drugs. In order to probe the role of the S768I mutation in NSCLC, we performed molecular dynamics (MD) simulations, essential dynamics (ED) analyses, and free energy landscape (FEL) constructions on WT and S768I mutant EGFR. MD simulations suggest that the S768I mutation increases both of the global and local flexibility of EGFR. The large concerted motions derived from ED analyses indicate that two important structural elements A-loop and αC-helix which distinguish the active state from the inactive state both have a more pronounced tendency to transition to the active state in S768I mutant than in WT. The free energy calculations reveal a more rugged and complex FEL for the S768I mutant than for the WT EGFR, implying that the mutant form has a richer conformational diversity. The study provides a reasonable molecular mechanism explanation for S768I mutations leading to NSCLC, and provide assistance for the development of new targeted therapeutic drugs for patients with S768I mutations. [ABSTRACT FROM AUTHOR]

Platelet-derived growth factor receptor beta (PDGFRβ) belongs to the receptor tyrosine kinase (RTK) protein family and is implicated in several disorders such as hematopoietic, glial, and soft-tissue cancer, non-cancerous disorders, including skeletal defects, brain calcification, and vascular anomalies. The research on small molecule inhibitors targeting PDGFRβ in cancer treatment has seen promising developments, but significant gaps remain. PDGFRβ, receptor tyrosine kinase, is overexpressed in various cancers and plays an important role in tumor progression, making it a potential therapeutic target. However, despite advances in identifying and characterizing PDGFRβ inhibitors, few have progressed to clinical trials, and the mechanistic details of PDGFRβ′s interactions with small molecule inhibitors are still not fully understood. Moreover, the specificity and selectivity of these inhibitors remain challenging, as off-target effects can lead to unwanted toxicity. In this investigation, two compounds, Genostrychnine and Chelidonine, were discovered that help inhibit the kinase activity of PDGFRβ. These small molecules were identified by employing various parameters involved in the drug discovery process, such as Lipinski’s rule of five (RO5), 2D similarity search and 3D pharmacophore-based virtual screening followed by MD simulation studies. The identified molecules were found to be effective and significantly bound with the PDGFRβ kinase domain. Overall, our findings demonstrate that these small drug-like compounds can be beneficial tools in studying the properties of PDGFRβ and can play a crucial role in the therapeutic development of cancers and other associated diseases.

A new theobromine-derived EGFR inhibitor (2-(3,7-Dimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-1-yl)-N-(2,6-dimethylphenyl)acetamide) has been developed that has the essential structural characteristics to interact with EGFR's pocket. The designed compound is 2,6-di ortho methylphenyl)acetamide derivative of the well-known alkaloid, theobromine, (T-1-DOMPA). Firstly, deep DFT studies have been conducted to study the optimized chemical structure, molecular orbital and chemical reactivity analysis of T-1-DOMPA. Then, T-1-DOMPA's anticancer potentialities were estimated first through a structure-based computational approach. Utilizing molecular docking, molecular dynamics, MD, simulations over 100 ns, MM-PBSA and PLIP studies, T-1-DOMPA bonded to and inhibited the EGFR protein effectively. Subsequently, the ADMET profiles of T-1-DOMPA were computed before preparation, and its drug-likeness was anticipated. Therefore, T-1-DOMPA was prepared for the purposes of scrutinizing both the design and the results obtained in silico. The in vitro potential of T-1-DOMPA against triple-negative breast cancer cell lines, MDA- MB-231, was very promising with an IC50 value of1.8 µM, comparable to the reference drug (0.9 µM), and a much higher selectivity index of 2.6. Interestingly, T-1-DOMPA inhibited three other cancer cell lines (CaCO-2, HepG-2, and A549) with IC50 values of 1.98, 2.53, and 2.39 µM exhibiting selectivity index values of 2,4, 1.9, and 2, respectively. Additionally, T-1-DOMPA prevented effectively the MDA-MB-231cell line's healing and migration abilities. Also, T-1-DOMPA's abilities to induce apoptosis were confirmed by acridine orange/ethidium bromide (AO/EB) staining assay. Finally, T-1-DOMPA caused an up-regulation of the gene expression of the apoptotic gene, Caspase-3, in the treated MDA-MB-231cell. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the potential of patuletin, a rare natural flavonoid, as a virulence and LasR inhibitor against Pseudomonas aeruginosa. Various computational studies were utilized to explore the binding of Patuletin and LasR at a molecular level. Molecular docking revealed that Patuletin strongly interacted with the active pocket of LasR, with a high binding affinity value of -20.96 kcal/mol. Further molecular dynamics simulations, molecular mechanics generalized Born surface area (MM/GBSA), protein-ligand interaction profile (PLIP), and essential dynamics analyses confirmed the stability of the patuletin-LasR complex, and no significant structural changes were observed in the LasR protein upon binding. Key amino acids involved in binding were identified, along with a free energy value of -26.9 kcal/mol. In vitro assays were performed to assess patuletin's effects on P. aeruginosa. At a sub-inhibitory concentration (1/4 MIC), patuletin significantly reduced biofilm formation by 48% and 42%, decreased pyocyanin production by 24% and 14%, and decreased proteolytic activities by 42% and 20% in P. aeruginosa isolate ATCC 27853 (PA27853) and P. aeruginosa clinical isolate (PA1), respectively. In summary, this study demonstrated that patuletin effectively inhibited LasR activity in silico and attenuated virulence factors in vitro, including biofilm formation, pyocyanin production, and proteolytic activity. These findings suggest that patuletin holds promise as a potential therapeutic agent in combination with antibiotics to combat antibiotic-tolerant P. aeruginosa infections. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the potential of patuletin, a rare natural flavonoid, as a virulence and LasR inhibitor against Pseudomonas aeruginosa. Various computational studies were utilized to explore the binding of Patuletin and LasR at a molecular level. Molecular docking revealed that Patuletin strongly interacted with the active pocket of LasR, with a high binding affinity value of −20.96 kcal/mol. Further molecular dynamics simulations, molecular mechanics generalized Born surface area (MM/GBSA), protein-ligand interaction profile (PLIP), and essential dynamics analyses confirmed the stability of the patuletin-LasR complex, and no significant structural changes were observed in the LasR protein upon binding. Key amino acids involved in binding were identified, along with a free energy value of −26.9 kcal/mol. In vitro assays were performed to assess patuletin’s effects on P. aeruginosa. At a sub-inhibitory concentration (1/4 MIC), patuletin significantly reduced biofilm formation by 48% and 42%, decreased pyocyanin production by 24% and 14%, and decreased proteolytic activities by 42% and 20% in P. aeruginosa isolate ATCC 27853 (PA27853) and P. aeruginosa clinical isolate (PA1), respectively. In summary, this study demonstrated that patuletin effectively inhibited LasR activity in silico and attenuated virulence factors in vitro, including biofilm formation, pyocyanin production, and proteolytic activity. These findings suggest that patuletin holds promise as a potential therapeutic agent in combination with antibiotics to combat antibiotic-tolerant P. aeruginosa infections.

Metamorphic, or fold-switching, proteins feature different folds that are physiologically relevant. The human chemokine XCL1 (or Lymphotactin) is a metamorphic protein that features two native states, an α - β and an all - β fold, which have similar stability at physiological condition. Here, extended molecular dynamics (MD) simulations, principal component analysis of atomic fluctuations and thermodynamic modeling based on both the configurational volume and free energy landscape, are used to obtain a detailed characterization of the conformational thermodynamics of human Lymphotactin and of one of its ancestors (as was previously obtained by genetic reconstruction). Comparison of our computational results with the available experimental data show that the MD-based thermodynamics can explain the experimentally observed variation of the conformational equilibrium between the two proteins. In particular, our computational data provide an interpretation of the thermodynamic evolution in this protein, revealing the relevance of the configurational entropy and of the shape of the free energy landscape within the essential space (i.e., the space defined by the generalized internal coordinates providing the largest, typically non-Gaussian, structural fluctuations). [ABSTRACT FROM AUTHOR]

Analysing protein conformational ensembles whether from molecular dynamics (MD) simulation or other sources for functionally relevant conformational changes can be very challenging. In the nineteen nineties dimensional reduction methods were developed primarily for analysing MD trajectories to determine dominant motions with the aim of understanding their relationship to function. Coarse-graining methods were also developed so the conformational change between two structures could be described in terms of the relative motion of a small number of quasi-rigid regions rather than in terms of a large number of atoms. When these methods are combined, they can characterize the large-scale motions inherent in a conformational ensemble providing insight into possible functional mechanism. The dimensional reduction methods first applied to protein conformational ensembles were referred to as Quasi-Harmonic Analysis, Principal Component Analysis and Essential Dynamics Analysis. A retrospective on the origin of these methods is presented, the relationships between them explained, and more recent developments reviewed. [ABSTRACT FROM AUTHOR]

Oxya chinensis sinuosa (rice field grasshopper) is an edible insect with numerous health beneficial properties, traditionally being used to treat many ailments in Korea and other countries. O. chinensis sinuosa has been used from centuries, however, a little is known about the chemical functionality of its bioactive compounds. Therefore, this study examined the anti-inflammatory and cathepsin C inhibitory activities of N-acetyldopamine dimer (2R, 3S)-2-(3′,4′-dihydroxyphenyl)-3-acetylamino-7-(N-acetyl-2″-aminoethyl)-1,4-benzodioxane (DAB1) isolated from O. chinensis sinuosa. Results showed that DAB1 reduced the expression of pro-inflammatory mediator (iNOS, COX-2) and cytokines (TNF-α, IL-1β, and IL-6), and curtailed the nuclear translocation of NF-κB by inhibiting the phosphorylation of IκBα in lipopolysaccharide stimulated macrophages. Additionally, DAB1 inhibited cathepsin C activity at the cellular level, supported by in vitro assay (Ki, 71.56 ± 10.21 µM and Kis, 133.55 ± 18.2 µM). Moreover, combinatorial molecular simulation and binding free energy analysis suggested a significant stability and binding affinity of cathepsin C-DAB1 complex via formation of hydrogen bond and hydrophobic interactions with the catalytic residues (Gln228, Thr379, Asn380, and Hie381). Also, essential dynamics analysis showed DAB1 induced non-functional motions in cathepsin C structure. Collectively, DAB1 was concluded as anti-inflammatory and cathepsin C inhibiting agent and could be used in the drug development against respective diseases.

The introduction of CRISPR/Cas9 based gene editing has greatly accelerated therapeutic genome editing. However, the off-target DNA cleavage by CRISPR/Cas9 protein hampers its clinical translation, hindering its widespread use as a programmable genome editing tool. Although Cas9 variants with better mismatch discrimination have been developed, they have significantly lower rates of on-target DNA cleavage. Here, we have compared the dynamics of a more specific naturally occurring Cas9 from Francisella novicida (FnCas9) to the most widely used, SpCas9 protein. Long-scale atomistic MD simulation of free and gRNA bound forms of both the Cas9 proteins was performed, and their domain rearrangements and binding affinity with gRNA were compared to decipher the possible reason behind the enhanced specificity of FnCas9 protein. The greater binding affinity with gRNA, high domain electrostatics, and more volatility of FnCas9 than SpCas9 may explain its increased specificity and lower tolerance for mismatches.

The present study consists in a novel computational protocol to model the UV-circular dichroism spectra of solvated species. It makes use of quantum-chemical calculations on a series of conformations of a flexible chromophore or on a series of chromophore/solvent clusters extracted from molecular dynamic simulations. The protocol is described and applied to the aqueous cationic tripeptide GAG+ and to the aqueous neutral decapeptide (GVGVP)2. The protocol has proven able to: (i) properly consider the conformational motion of solute in the given environment; (ii) give the actual statistical weight of each conformational state; (iii) provide a reliable quantum mechanical method able to reproduce the spectral features. Temperature effects on conformations and spectral properties are properly taken into account. The role of explicit solvent on the conformational analysis and the spectra calculation is discussed. The comparison of the calculated circular dichroism spectra with experimental ones recorded at different temperatures represents a strict validation test of the method. [ABSTRACT FROM AUTHOR]

Abstract Background Principal component analysis (PCA) is commonly applied to the atomic trajectories of biopolymers to extract essential dynamics that describe biologically relevant motions. Although application of PCA is straightforward, specialized software to facilitate workflows and analysis of molecular dynamics simulation data to fully harness the power of PCA is lacking. The Java Essential Dynamics inspector (JEDi) software is a major upgrade from the previous JED software. Results Employing multi-threading, JEDi features a user-friendly interface to control rapid workflows for interrogating conformational motions of biopolymers at various spatial resolutions and within subregions, including multiple chain proteins. JEDi has options for Cartesian-based coordinates (cPCA) and internal distance pair coordinates (dpPCA) to construct covariance (Q), correlation (R), and partial correlation (P) matrices. Shrinkage and outlier thresholding are implemented for the accurate estimation of covariance. The effect of rare events is quantified using outlier and inlier filters. Applying sparsity thresholds in statistical models identifies latent correlated motions. Within a hierarchical approach, small-scale atomic motion is first calculated with a separate local cPCA calculation per residue to obtain eigenresidues. Then PCA on the eigenresidues yields rapid and accurate description of large-scale motions. Local cPCA on all residue pairs creates a map of all residue-residue dynamical couplings. Additionally, kernel PCA is implemented. JEDi output gives high quality PNG images by default, with options for text files that include aligned coordinates, several metrics that quantify mobility, PCA modes with their eigenvalues, and displacement vector projections onto the top principal modes. JEDi provides PyMol scripts together with PDB files to visualize individual cPCA modes and the essential dynamics occurring within user-selected time scales. Subspace comparisons performed on the most relevant eigenvectors using several statistical metrics quantify similarity/overlap of high dimensional vector spaces. Free energy landscapes are available for both cPCA and dpPCA. Conclusion JEDi is a convenient toolkit that applies best practices in multivariate statistics for comparative studies on the essential dynamics of similar biopolymers. JEDi helps identify functional mechanisms through many integrated tools and visual aids for inspecting and quantifying similarity/differences in mobility and dynamic correlations.

Serum and glucocorticoid-regulated kinase 1 (SGK1) is a Ser/Thr protein kinase involved in regulating cell survival, growth, proliferation, and migration. Its elevated expression and dysfunction are reported in breast, prostate, hepatocellular, lung adenoma, and renal carcinomas. We have analyzed the SGK1 mutations to explore their impact at the sequence and structure level by utilizing state-of-the-art computational approaches. Several pathogenic and destabilizing mutations were identified based on their impact on SGK1 and analyzed in detail. Three amino acid substitutions, K127M, T256A, and Y298A, in the kinase domain of SGK1 were identified and incorporated structurally into original coordinates of SGK1 to explore their time evolution impact using all-atom molecular dynamic (MD) simulations for 200 ns. MD results indicate substantial conformational alterations in SGK1, thus its functional loss, particularly upon T256A mutation. This study provides meaningful insights into SGK1 dysfunction upon mutation, leading to disease progression, including cancer, and neurodegeneration.

Caterina Arcangeli,1 Chiara Lico,2 Selene Baschieri,2 Mariateresa Mancuso3 1Laboratory of Health and Environment, Italian National Agency for New Technologies, Energy and Sustainable Economic Development, ENEA, Rome, Italy; 2Laboratory of Biotechnology, Italian National Agency for New Technologies, Energy and Sustainable Economic Development, ENEA, Rome, Italy; 3Laboratory of Biomedical Technologies, Italian National Agency for New Technologies, Energy and Sustainable Economic Development, ENEA, Rome, ItalyCorrespondence: Caterina Arcangeli; Mariateresa MancusoENEA, Italian National Agency for New Technologies, Energy and Sustainable Economic Development, Casaccia Research Centre, Via Anguillarese 301, Rome 00123, ItalyTel +39 06 3048 6898/4993Fax +39 06 3048 6559/3644Email caterina.arcangeli@enea.it; mariateresa.mancuso@enea.itIntroduction: The new frontier of tumor diagnosis and treatment relies on the development of delivery strategies capable of allowing the specific targeting of the diagnostic agents/chemotherapeutics, avoiding side effects. In the case of brain tumors, achieving this goal is made more difficult by the presence of the blood–brain barrier (BBB). Peptides have been revealed as excellent candidates for both BBB crossing and specific cancer homing. Nanoparticles (NPs), functionalized with BBB crossing and tumor homing (TH) peptides, are emerging as smart theranostic systems. However, there is still poor knowledge concerning the molecular structure and dynamical properties of these peptides, essential requirements for a suitable functionalization of the delivery systems themselves.Methods: In this work, by means of molecular dynamics (MD) simulations, we have extensively characterized the structural and dynamical behavior of several peptides, known to be endowed of BBB crossing and TH properties.Results: The simulations point out that, on the basis of their conformational dynamics, the peptides can be classified in two main groups: 1) peptides assuming a specific structural conformation, a feature that could be important for interacting with the molecular target but that may limit their use as functionalizing molecules and 2) highly flexible peptides whose interaction with the target may be independent of a particular structural conformation and that may represent good candidates for the functionalization of theranostic NP-based platforms.Discussion: Such findings may be useful for the de novo designing of NP-based delivery systems.Keywords: conformational flexibility, free energy landscapes, essential dynamics, peptides, brain, theranostic platform

Background: Principal component analysis (PCA) is commonly applied to the atomic trajectories of biopolymers to extract essential dynamics that describe biologically relevant motions. Although application of PCA is straightforward, specialized software to facilitate workflows and analysis of molecular dynamics simulation data to fully harness the power of PCA is lacking. The Java Essential Dynamics inspector (JEDi) software is a major upgrade from the previous JED software. Results: Employing multi-threading, JEDi features a user-friendly interface to control rapid workflows for interrogating conformational motions of biopolymers at various spatial resolutions and within subregions, including multiple chain proteins. JEDi has options for Cartesian-based coordinates (cPCA) and internal distance pair coordinates (dpPCA) to construct covariance (Q), correlation (R), and partial correlation (P) matrices. Shrinkage and outlier thresholding are implemented for the accurate estimation of covariance. The effect of rare events is quantified using outlier and inlier filters. Applying sparsity thresholds in statistical models identifies latent correlated motions. Within a hierarchical approach, small-scale atomic motion is first calculated with a separate local cPCA calculation per residue to obtain eigenresidues. Then PCA on the eigenresidues yields rapid and accurate description of large-scale motions. Local cPCA on all residue pairs creates a map of all residue-residue dynamical couplings. Additionally, kernel PCA is implemented. JEDi output gives high quality PNG images by default, with options for text files that include aligned coordinates, several metrics that quantify mobility, PCA modes with their eigenvalues, and displacement vector projections onto the top principal modes. JEDi provides PyMol scripts together with PDB files to visualize individual cPCA modes and the essential dynamics occurring within user-selected time scales. Subspace comparisons performed on the most relevant eigenvectors using several statistical metrics quantify similarity/overlap of high dimensional vector spaces. Free energy landscapes are available for both cPCA and dpPCA. Conclusion: JEDi is a convenient toolkit that applies best practices in multivariate statistics for comparative studies on the essential dynamics of similar biopolymers. JEDi helps identify functional mechanisms through many integrated tools and visual aids for inspecting and quantifying similarity/differences in mobility and dynamic correlations. [ABSTRACT FROM AUTHOR]

Precision medicine has revolutionized modern cancer therapeutic management by targeting specific molecular aberrations responsible for the onset and progression of tumorigenesis. ROS proto-oncogene 1 (ROS1) is a receptor tyrosine kinase (RTK) that can induce tumorigenesis through various signaling pathways, such as cell proliferation, survival, migration, and metastasis. It has emerged as a promising therapeutic target in various cancer types. However, there is very limited availability of specific ROS1 inhibitors for therapeutic purposes. Exploring repurposed drugs for rapid and effective treatment is a useful approach. In this study, we utilized an integrated approach of virtual screening and molecular dynamics (MD) simulations of repurposing existing drugs for ROS1 kinase inhibition. Using a curated library of 3648 FDA-approved drugs, virtual screening identified drugs capable of binding to ROS1 kinase domain. The results unveil two hits, Midostaurin and Alectinib with favorable binding profiles and stable interactions with the active site residues of ROS1. These hits were subjected to stability assessment through all-atom MD simulations for 200 ns. MD results showed that Midostaurin and Alectinib were stable with ROS1. Taken together, the study showed a rational framework for the selection of repurposed Midostaurin and Alectinib with ROS1 inhibitory potential for therapeutic management after further validation., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Alrouji, Yasmin, Alhumaydhi, Sharaf, Shahwan and Shamsi.)

Abstract Background Essential Dynamics (ED) is a common application of principal component analysis (PCA) to extract biologically relevant motions from atomic trajectories of proteins. Covariance and correlation based PCA are two common approaches to determine PCA modes (eigenvectors) and their eigenvalues. Protein dynamics can be characterized in terms of Cartesian coordinates or internal distance pairs. In understanding protein dynamics, a comparison of trajectories taken from a set of proteins for similarity assessment provides insight into conserved mechanisms. Comprehensive software is needed to facilitate comparative-analysis with user-friendly features that are rooted in best practices from multivariate statistics. Results We developed a Java based Essential Dynamics toolkit called JED to compare the ED from multiple protein trajectories. Trajectories from different simulations and different proteins can be pooled for comparative studies. JED implements Cartesian-based coordinates (cPCA) and internal distance pair coordinates (dpPCA) as options to construct covariance (Q) or correlation (R) matrices. Statistical methods are implemented for treating outliers, benchmarking sampling adequacy, characterizing the precision of Q and R, and reporting partial correlations. JED output results as text files that include transformed coordinates for aligned structures, several metrics that quantify protein mobility, PCA modes with their eigenvalues, and displacement vector (DV) projections onto the top principal modes. Pymol scripts together with PDB files allow movies of individual Q- and R-cPCA modes to be visualized, and the essential dynamics occurring within user-selected time scales. Subspaces defined by the top eigenvectors are compared using several statistical metrics to quantify similarity/overlap of high dimensional vector spaces. Free energy landscapes can be generated for both cPCA and dpPCA. Conclusions JED offers a convenient toolkit that encourages best practices in applying multivariate statistics methods to perform comparative studies of essential dynamics over multiple proteins. For each protein, Cartesian coordinates or internal distance pairs can be employed over the entire structure or user-selected parts to quantify similarity/differences in mobility and correlations in dynamics to develop insight into protein structure/function relationships.

The dengue virus (DENV) infects approximately 400 million people annually worldwide causing significant morbidity and mortality. Despite advances in understanding the virus life cycle and infectivity, no specific treatment for this disease exists due to the lack of therapeutic drugs. In addition, vaccines available currently are ineffective with severe side effects. Therefore, there is an urgent need for developing therapeutics suitable for effective management of DENV infection. In this study, we adopted a drug repurposing strategy to identify new therapeutic use of existing FDA approved drug molecules to target DENV2 non-structural proteins NS3 and NS5 using computational approaches. We used Drugbank database molecules for virtual screening and multiple docking analysis against a total of four domains, the NS3 protease and helicase domains and NS5 MTase and RdRp domains. Subsequently, MD simulations and MM-PBSA analysis were performed to validate the intrinsic atomic interactions and the binding affinities. Furthermore, the internal dynamics in all four protein domains, in presence of drug molecule binding were assessed using essential dynamics and free energy landscape analyses, which were further coupled with conformational dynamics-based clustering studies and cross-correlation analysis to map the regions that exhibit these structural variations. Our comprehensive analysis identified tolcapone, cefprozil, delavirdine and indinavir as potential inhibitors of NS5 MTase, NS5 RdRp, NS3 protease and NS3 helicase functions, respectively. These high-confidence candidate molecules will be useful for developing effective anti-DENV therapy to combat dengue infection.

Heparanase (HPSE) is an endo-β-D-glucuronidase that has diverse functions in mammals which includes cell survival, cell adhesion and cell migration. HPSE features both enzymatic and non-enzymatic functionalities in a pH dependent manner. Hence, in this study, an extensive molecular dynamics simulation, molecular docking, protein Angular dispersion analysis were performed for apo form and holo forms to understand its conformational changes at varied pH conditions. On comparative conformational analysis of apo and holo forms, it was inferred that the HSPE has undergone pH dependent structural changes, thereby affecting the binding of Heparan sulfate proteoglycan (HSPG). Moreover, HPSE also showed favourable structural changes for optimal binding of HSPG at pH 5.0 and 6.0, as inferred from functional flap displacements within HPSE. Thus, this study provides significant insights on optimal pH for HPSE to exhibit its enzymatic activity. The outcome of this study shall aid in ideal lead generation for targeting HPSE mediated disease conditions. [ABSTRACT FROM AUTHOR]

Background Retinoic acid inducible gene 1 (RIG-1), multi-domain protein has a role-play in detecting viral nucleic acids and stimulates the antiviral response. Dysfunction of this protein due to mutations makes the route vulnerable to viral diseases. Aim Identification of functional hotspots that maintains conformational stability in RIG-1 domains. Methods In this study, we employed a systematic in silico strategy on RIG-1 protein to understand the mechanism of structural changes upon mutation. We computationally investigated the protein sequence signature for all the three domains of RIG-1 protein that encloses the mutation within the motif. Further, we carried out a structural comparison between RIG-1 domains with their respective distant orthologs which revealed the minimal number of interactions required to maintain its structural fold. This intra-protein network paved the way to infer hotspot residues crucial for the maintenance of the structural architecture and folding pattern. Key findings Our analysis revealed about 40 hotspot residues that determine the folding pattern of the RIG-1 domains. Also, conventional molecular dynamic simulation coupled with essential dynamics provides conformational transitions of hot spot residues among native and mutant structures. Structural variations owing to hotspot residues in mutants again confirm the significance of these residues in structural characterization of RIG-1 domains. We believe our results will help the researchers to better comprehend towards regulatory regions and target-binding sites for therapeutic design within the pattern recognition receptor proteins. Significance Our protocol employed in this work describes a novel approach in identifying signature residues that would provide structural insights in protein folding. [ABSTRACT FROM AUTHOR]

Cytochrome c (cyt- c ) upon binding with cardiolipin acquires peroxidase activity and is strictly connected to the pathogenesis of many human diseases including neurodegenerative and cardiovascular diseases. Interaction of cyt- c with cardiolipin mimics partial unfolding/conformational changes of cyt- c in different solvent environments. Dynamic pictures of these conformational changes of cyt- c are crucial in understanding their physiological roles in mitochondrial functions. Therefore, atomistic molecular dynamics (MD) simulations have been carried out to investigate the effect of different solvents (water, urea/water, MeOH and DMSO) on the structure and conformations of apoptotic cyt- c (Fe 3+ ). Our study demonstrates that the structural changes in the protein are solvent dependent. The structural differences are observed majorly on the β-sheets and α-helical conformations and the degree of their perturbation are specific to the solvent. Although a complete loss of β-sheets (0%) is observed in MeOH and DMSO, by contrast, well preserved β-sheets (3.84%) are observed in water and urea/water. A significant decrease in the α-helical contents is observed in MeOH (41.34%) and water (42.46%), a negligible alteration in DMSO (44.25%) and well preserved α-helical (45.19%) contents in urea/water. The distances between the residues critical for electron transfer are decreased considerably for DMSO. Further, the reduction in residue flexibility and the conformational space indicate that the collective motions of cyt- c are reduced when compared to other cosolvents. Essential dynamics analysis implies that the overall motions of cyt- c in water, MeOH and urea/water are involved in three to four eigenvectors and in first eigenvector in DMSO. Overall, we believe that MD simulations of cyt- c in different solvents can provide a detailed microscopic understanding of the physiological roles, electron transport and peroxidase function in the early events of apoptosis which are hard to probe experiments. [ABSTRACT FROM AUTHOR]

ABSTRACT Bcl-xl protein has a long unstructured loop attached to its structured region which joins two helices. The necessity to have this unstructured segment in Bcl-xl is not yet well understood. To what extent the unstructured segment can influence the dynamics of the structured region of protein, with potential to influence the function, has been investigated in this work. Molecular dynamics simulation and principal component analysis show how the loop affects the internal motions of the protein, particularly its ligand binding pocket. Generally an unstructured region in the structure would promote flexibility resulting entropic stability but in contrary, here it narrows down the conformational space of the structured region of protein that could be hypothesized to impact the functional precision. Effects of the loop propagate to the binding pocket through structural rearrangements of polar side chains. The immediate suspicion of possible impact of phosphorylation to modulate the function of the protein is proven to be a fact, as the phosphorylated S49 and S62 located on the large unstructured region are seen to perturb the electrostatic network of the structure; an observation that validates and clarifies the role of loop as a modulator through biophysical and biochemical mechanisms. Proteins 2017; 85:1567-1579. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Transition of a physiological folded prion (Pr PC) into a pathogenic misfolded prion (Pr PSc) causes lethal neurodegenerative disorders and prion diseases. Antiprion compounds have been developed to prevent this conversion; however, their mechanism of action remains unclear. Recently, we reported two antiprion compounds, BMD29 and BMD35, identified by in silico and in vitro screening. In this study, we used extensive explicit-solvent molecular dynamics simulations to investigate ligand-binding inhibition by antiprion compounds in prion folding over misfolding behavior at acidic pH. The two antiprion compounds and the previously reported GN8 compound resulted in a remarkably stabilized intermediate by binding to the hotspot region of Pr PC, whereas free Pr PC and the inactive compound BMD01 destabilized the structure of Pr PC leading to the misfolded form. The results uncovered a secondary structural transition of free Pr PC and transition suppression by the antiprion compounds. One of the major misfolding processes in Pr PC, alternation of hydrophobic core residues, disruption of intramolecular interactions, and the increase in residue solvent exposure were significantly inhibited by both antiprion compounds. These findings provide insights into prion misfolding and inhibition by antiprion compounds. [ABSTRACT FROM AUTHOR]

Background: Essential Dynamics (ED) is a common application of principal component analysis (PCA) to extract biologically relevant motions from atomic trajectories of proteins. Covariance and correlation based PCA are two common approaches to determine PCA modes (eigenvectors) and their eigenvalues. Protein dynamics can be characterized in terms of Cartesian coordinates or internal distance pairs. In understanding protein dynamics, a comparison of trajectories taken from a set of proteins for similarity assessment provides insight into conserved mechanisms. Comprehensive software is needed to facilitate comparative-analysis with user-friendly features that are rooted in best practices from multivariate statistics. Results: We developed a Java based Essential Dynamics toolkit called JED to compare the ED from multiple protein trajectories. Trajectories from different simulations and different proteins can be pooled for comparative studies. JED implements Cartesian-based coordinates (cPCA) and internal distance pair coordinates (dpPCA) as options to construct covariance (Q) or correlation (R) matrices. Statistical methods are implemented for treating outliers, benchmarking sampling adequacy, characterizing the precision of Q and R, and reporting partial correlations. JED output results as text files that include transformed coordinates for aligned structures, several metrics that quantify protein mobility, PCA modes with their eigenvalues, and displacement vector (DV) projections onto the top principal modes. Pymol scripts together with PDB files allow movies of individual Q- and R-cPCA modes to be visualized, and the essential dynamics occurring within user-selected time scales. Subspaces defined by the top eigenvectors are compared using several statistical metrics to quantify similarity/overlap of high dimensional vector spaces. Free energy landscapes can be generated for both cPCA and dpPCA. Conclusions: JED offers a convenient toolkit that encourages best practices in applying multivariate statistics methods to perform comparative studies of essential dynamics over multiple proteins. For each protein, Cartesian coordinates or internal distance pairs can be employed over the entire structure or user-selected parts to quantify similarity/differences in mobility and correlations in dynamics to develop insight into protein structure/function relationships. [ABSTRACT FROM AUTHOR]

Osmolytes play an important role in cellular physiology by modulating the properties of proteins, including their molecular specificity. EcoRI is a model restriction enzyme whose specificity to DNA is altered in the presence of osmolytes. Here, we investigate the effect of two different osmolytes, glycerol and DMSO, on the dynamics and hydration of the EcoRI enzyme using molecular dynamics simulations. Our results show that the osmolytes, alter the essential dynamics of EcoRI. Particularly, we observe that the dynamics of the arm region of EcoRI which is involved in DNA binding is significantly altered. In addition, conformational free energy analyses reveals that the osmolytes bring about a change in the landscape similar to that of EcoRI bound to cognate DNA. We further observe that the hydration of the enzyme for each of the osmolyte is different, indicating that the mechanism of action of each of these osmolytes could be different. Further analyses of interfacial water dynamics using rotational autocorrelation function reveals that while the protein surface contributes to a slower tumbling motion of water, osmolytes, additionally contribute to the slowing of the angular motion of the water molecules. Entropy analysis also corroborates with this finding. We also find that the slowed rotational motion of interfacial waters in the presence of osmolytes contributes to a slowed relaxation of the hydrogen bonds between the interfacial waters and the functionally important residues in the protein. Taken together, our results show that osmolytes alter the dynamics of the protein by altering the dynamics of water. This altered dynamics, mediated by the changes in the water dynamics and hydrogen bonds with functionally important residues, may contribute to the altered specificity of EcoRI in the presence of osmolytes. [Display omitted] • Osmolytes alter the essential dynamics of EcoRI significantly in the DNA binding enfolding arms. • Dehydration in the interfacial region is osmolyte-dependent. • Osmolytes alter the dynamics of water in the interfacial region of EcoRI. • Osmolytes tend to change the conformational equilibrium of the free EcoRI , making it poised for DNA binding. • All of these together contribute to the altered specificity of EcoRI in the presence of osmolytes. [ABSTRACT FROM AUTHOR]

The opening/closure of the catalytic loop 6 over the active site in apo triosephosphate isomerase (TIM) has been previously shown to be driven by the global motions of the enzyme, specifically the counter-clockwise rotation of the subunits. In this work, the effect of the substrate dihydroxyacetone phosphate (DHAP) on TIM dynamics is assessed using two apo and two DHAP-bound molecular dynamics (MD) trajectories (each 60 ns long). Multiple events of catalytic loop opening/closure take place during 60 ns runs for both apo TIM and its DHAP-complex. However, counter-clockwise rotation observed in apo TIM is suppressed and bending-type motions are linked to loop dynamics in the presence of DHAP. Bound DHAP molecules also reduce the overall mobility of the enzyme and change the pattern of orientational cross-correlations, mostly those within each subunit. The fluctuations of pseudodihedral angles of the loop 6 residues are enhanced towards the C-terminus, when DHAP is bound at the active site.

ABSTRACT The cold denaturation of globular proteins is a process that can be caused by increasing pressure or decreasing the temperature. Currently, the action mechanism of this process has not been clearly understood, raising an interesting debate on the matter. We have studied the process of cold denaturation using molecular dynamics simulations of the frataxin system Yfh1, which has a dynamic experimental characterization of unfolding at low and high temperatures. The frataxin model here studied allows a comparative analysis using experimental data. Furthermore, we monitored the cold denaturation process of frataxin and also investigated the effect under the high-pressure regime. For a better understanding of the dynamics and structural properties of the cold denaturation, we also analyzed the MD trajectories using essentials dynamic. The results indicate that changes in the structure of water by the effect of pressure and low temperatures destabilize the hydrophobic interaction modifying the solvation and the system volume leading to protein denaturation. Proteins 2016; 85:125-136. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The water-soluble glutathione-protected [Au 25 (GSH) 18 ] -1 nanocluster was investigated by integrating several methodologies such as molecular dynamics simulations, essential dynamics analysis, and state-of-the-art time-dependent density functional theory calculations. Fundamental aspects such as conformational, weak interactions and solvent effects, especially hydrogen-bonds, were included and found to play a fundamental role in assessing the optical response of this system. Our analysis demonstrated not only that the electronic circular dichroism is extremely sensitive to the solvent presence but also that the solvent itself plays an active role in the optical activity of such system, forming a chiral solvation shell around the cluster. Our work demonstrates a successful strategy to investigate in detail chiral interfaces between metal nanoclusters and their environments, applicable, e.g., to chiral electronic interactions between clusters and biomolecules.

β-secretase 1 (BACE1) initiates the proteolysis of amyloid precursor protein (APP) to generate Aβ, aggregation of which has been considered to be the main histopathological feature of Alzheimer's Disease. Here, we have explored the conformational switching of BACE1 during APP recognition using molecular dynamics simulation thereby suggesting the recognition to be a conformational selection process. Free BACE1 is highly flexible and exists as an ensemble of conformations. The β-hairpin flap that covers the active site of BACE1 visits numerous conformations during the simulation. Essential dynamics reveal that concerted movements in several loops including the flap region lead to a conformational switching from open to closed form. During the simulation, free BACE1 visits both the open and closed forms multiple times. Binding of APP to the BACE1 cavity shifts the equilibrium towards a stable complex stabilized by strong electrostatic surface complementarity along with several van der Waals and hydrogen bonding interactions. [ABSTRACT FROM AUTHOR]

Abnormal activation of EGFR is associated with human cancer, and thus it is a key target for inhibition in cancer therapy. There is evidence suggesting that the activation mechanism of EGFR is based upon the formation of the asymmetric dimer of the kinase domains. Here, we performed MD simulations on the asymmetric dimer for both active and inactive conformations of EGFR kinase domain to investigate flexibility and intrinsic motions of the proteins. Simulations of the active conformation showed that the formation of the asymmetric dimer changes the dynamics of EGFR kinase domain by suppressing fluctuation of the protein and altering the direction of motion of the protein. In contrast, the asymmetric dimerization of the inactive conformation does not alter the overall fluctuation of the kinase domain and does not initiate destabilizing of the inactive structure. We also investigated the intermolecular interactions in the EGFR asymmetric dimers and found that in the active conformation the interactions are dominated by loop–loop contacts rather than those from the helix–helix interactions. In contrast, helix–helix interaction seemed to be more significant for the inactive kinase structure. This work helps us to better understand the conformational flexibility and dynamics of the EGFR kinase domain, as well as provides information that may be useful to develop newer classes of inhibitors that can block allosteric sites rather than the more traditional catalytic site. [ABSTRACT FROM AUTHOR]

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A comparison between different conformations of a given protein, relating both structure and dynamics, can be performed in terms of combined principal component analysis (combined-PCA). To that end, a trajectory is obtained by concatenating molecular dynamics trajectories of the individual conformations under comparison. Then, the principal components are calculated by diagonalizing the correlation matrix of the concatenated trajectory. Since the introduction of this approach in 1995 it has had a large number of applications. However, the interpretation of the eigenvectors and eigenvalues so obtained is based on intuitive foundations, because analytical expressions relating the concatenated correlation matrix with those of the individual trajectories under consideration have not been provided yet. In this article, we present such expressions for the cases of two, three, and an arbitrary number of concatenated trajectories. The formulas are simple and show what is to be expected and what is not to be expected from a combined-PCA. Their correctness and usefulness is demonstrated by discussing some representative examples. The results can be summarized in a simple sentence: the correlation matrix of a concatenated trajectory is given by the average of the individual correlation matrices plus the correlation matrix of the individual averages. From this it follows that the combined-PCA of trajectories belonging to different free energy basins provides information that could also be obtained by alternative and more straightforward means. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Essential Dynamics (ED) is a powerful tool for analyzing molecular dynamics (MD) simulations and it is widely adopted for conformational analysis of large molecular systems such as, for example, proteins and nucleic acids. In this study, we extend the use of ED to the study of clusters of arbitrary size constituted by weakly interacting particles, for example, atomic clusters and supramolecular systems. The key feature of the method we present is the identification of the relevant atomic-molecular clusters to be analyzed by ED for extracting the information of interest. The application of this computational approach allows a straightforward and unbiased conformational study of the local microstructures in liquids, as emerged from semiclassical MD simulations. The good performance of the method is demonstrated by calculating typical observables of liquid water, that is, NMR, NEXAFS O1s, and IR spectra, known to be rather sensitive both to the presence and to the conformational features of hydrogen-bonded clusters. [ABSTRACT FROM AUTHOR]

ABSTRACT Disintegrins, small molecular weight proteins contained in the venom of vipers and rattlesnakes, are high-affinity and selectivity integrin antagonists. Disintegrins inhibitory epitope mainly consists in a tripeptide sequence localized in a mobile loop protruding from the protein core. RTS and/or KTS tripeptide characterizes the most recently discovered group of disintegrins that selectively block α1β1 integrin receptor. A NMR study dedicated to structure and dynamics properties of jerdostatin, an RTS disintegrin, demonstrated that the substitution of the native RTS with KTS motif impaired flexibility and inhibitory activity of the molecule. Here we add atomic details to the experimental profiles of jerdostatin and its R24K mutant by analyzing the dynamics behavior of the molecules through computational methods. For jerdostatin wild type, molecular dynamics simulations and essential dynamics analyses showed that Y31 residue acts as hinge element in the concerted motions involving the active loop and the C-terminal tail. R24 side chain ability to engage both cation-π and H-bond interactions with Y31 residue was found crucial for that breathing mechanism. Less significant loop-tail concerted motions were observed for the R24K mutant. The description at atomic resolution of jerdostatin dynamics is useful for decoding the influence of specific residues on disintegrin functional properties. © 2014 Wiley Periodicals, Inc. Biopolymers 103: 158-166, 2015. [ABSTRACT FROM AUTHOR]

The study aims to gain insight into the mode of ligand recognition by tetratricopeptide repeat (TPR) domains of chloroplast translocon at the outer envelope of chloroplast (Toc64) and mitochondrial Om64, two paralogous proteins that mediate import of proteins into chloroplast and mitochondria, respectively. Chaperone proteins associate with precursor proteins in the cytosol to maintain them in a translocation competent conformation and are recognized by Toc64 and Om64 that are located on the outer membrane of the target organelle. Heat shock proteins (Hsp70) and Hsp90 are two chaperones, which are known to play import roles in protein import. The C-termini of these chaperones are known to interact with the TPR domain of chloroplast Toc64 and mitochondrial Om64 in Arabidopsis thaliana ( At). Using a molecular dynamics approach and binding energy calculations, we identify important residues involved in the interactions. Our findings suggest that the TPR domain from AtToc64 has higher affinity towards C-terminal residues of Hsp70. The interaction occurs as the terminal helices move towards each other enclosing the cradle on interaction of AtHsp70 with the TPR domain. In contrast, the TPR domain from AtOm64 does not discriminate between the C-termini of Hsp70 and Hsp90. These binding affinities are discussed with respect to our knowledge of protein targeting and specificity of protein import into endosymbiotic organelles in plant cells. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Papain like protease (PLpro) is a cysteine protease from the coronaviridae family of viruses. Coronaviruses possess a positive sense, single-strand RNA, leading to the translation of two viral polypeptides containing viral structural, non-structural and accessory proteins. PLpro is responsible for the cleavage of nsp1–3 from the viral polypeptide. PLpro also possesses deubiquitinating and deISGlyating activity, which sequesters the virus from the host's immune system. This indispensable attribute of PLpro makes it a protein of interest as a drug target. The present study aims to analyze the structural influences of ligand binding on PLpro. First, PLpro was screened against the ZINC-in-trials library, from which four lead compounds were identified based on estimated binding affinity and interaction patterns. Next, based on molecular docking results, ZINC000000596945, ZINC000064033452 and VIR251 (control molecule) were subjected to molecular dynamics simulation. The study evaluated global and essential dynamics analyses utilising principal component analyses, dynamic cross-correlation matrix, free energy landscape and time-dependant essential dynamics to predict the structural changes observed in PLpro upon ligand binding in a simulated environment. The MM/PBSA-based binding free energy calculations of the two selected molecules, ZINC000000596945 (−41.23 ± 3.70 kcal/mol) and ZINC000064033452 (−25.10 ± 2.65 kcal/mol), displayed significant values which delineate them as potential inhibitors of PLpro from SARS-CoV-2. [Display omitted] • PLpro is a indispensable viral protease. • The present study investigate structural influences of ligand binding on PLpro. • We have identified two promising lead candidates against PLpro. [ABSTRACT FROM AUTHOR]

Background To understand the effect of the long intracellular loop 3 (ICL3) on the intrinsic dynamics of human β2-adrenergic receptor, molecular dynamics (MD) simulations were performed on two different models, both of which were based on the inactive crystal structure in complex with carazolol (after removal of carazolol and T4-lysozyme). In the so-called loop model, the ICL3 region that is missing in available crystal structures was modeled as an unstructured loop of 32-residues length, whereas in the clipped model, the two open ends were covalently bonded to each other. The latter model without ICL3 was taken as a reference, which has also been commonly used in recent computational studies. Each model was embedded into POPC bilayer membrane with explicit water and subjected to a 1 μs molecular dynamics (MD) simulation at 310 K. Results After around 600 ns, the loop model started a transition to a "very inactive" conformation, which is characterized by a further movement of the intracellular half of transmembrane helix 6 (TM6) towards the receptor core, and a close packing of ICL3 underneath the membrane completely blocking the G-protein's binding site. Concurrently, the binding site at the extracellular part of the receptor expanded slightly with the Ser207-Asp113 distance increasing to 18 Å from 11 Å, which was further elaborated by docking studies. Conclusions The essential dynamics analysis indicated a strong coupling between the extracellular and intracellular parts of the intact receptor, implicating a functional relevance for allosteric regulation. In contrast, no such transition to the "very inactive" state, nor any structural correlation, was observed in the clipped model without ICL3. Furthermore, elastic network analysis using different conformers for the loop model indicated a consistent picture on the specific ICL3 conformational change being driven by global modes. [ABSTRACT FROM AUTHOR]

The C-terminus tail (G144-T149) of the hyperthermophile Sulfolobus tokodaii (Sto-RNase HI) plays an important role in this protein's hyperstabilization and may therefore be a good protein stability tag. Detailed understanding of the structural and dynamic effects of C-terminus tail deletion is required for gaining insights into the thermal stability mechanism of Sto-RNase HI. Focused on Sulfolobus tokodaii RNase HI (Sto-RNase HI) and its derivative lacking the C-terminal tail (ΔC6 Sto-RNase HI) (PDB codes: 2EHG and 3ALY), we applied molecular dynamics (MD) simulations at four different temperatures (300, 375, 475, and 500 K) to examine the effect of the C-terminal tail on the hyperstabilization of Sto-RNase HI and to investigate the unfolding process of Sto-RNase HI and ΔC6 Sto-RNase HI. The simulations suggest that the C-terminal tail has significant impact in hyperstabilization of Sto-RNase HI and the unfolding of these two proteins evolves along dissimilar pathways. Essential dynamics analysis indicates that the essential subspaces of the two proteins at different temperatures are non-overlapping within the trajectories and they exhibit different directions of motion. Our work can give important information to understand the three-state folding mechanism of Sto-RNase HI and to offer alternative strategies to improve the protein stability. [ABSTRACT FROM AUTHOR]

Abstract: We describe the application of molecular dynamics followed by principal component analysis to study the inter-domain movements of the ligand binding domain (LBD) of mGluR5 in response to the binding of selected agonists or antagonists. Our results suggest that the method is an attractive alternative to current approaches to predict the agonist-induced or antagonist-blocked LBD responses. The ratio between the eigenvalues of the first and second eigenvectors (R 1,2) is also proposed as a numerical descriptor for discriminating the ligand behavior as a mGluR5 agonist or antagonist. [Copyright &y& Elsevier]

Abstract: Three molecular dynamics (MD) simulation methods are used to follow the thermal unfolding of bovine β-lactoglobulin (β-lac). The methods used, classical MD simulation at different temperatures in the range 300–500 K, essential dynamics and replica exchange MD, were chosen to give a range of conventional and accelerated methods. At 350 K, just above the experimentally determined denaturation temperature of β-lac only small changes to the tertiary fold and secondary structure were seen during a 110 ns simulation. At 400 K and 450 K more unfolding was observed, but it was not until the temperature was increased to 500 K that substantial disruption to the protein structure was seen. For the time that the heated simulated β-lac molecules occupy the same conformation space, they appear to follow similar unfolding pathways. ED simulations biased along the first 5 eigenvectors (determined at 350 K) give rise to conformations that have a more elongated tertiary fold compared to heated simulations, and do not follow similar unfolding pathways to the heated simulations. The REMD simulation, which is the equivalent of an approximately 0.7 μs simulation at 350 K, shows a small degree of tertiary structure unfolding, but very little secondary structure change. The results are discussed in terms of the structural changes that have been observed to occur experimentally in β-lac. [Copyright &y& Elsevier]

The opening/closure of the catalytic loop 6 over the active site in apo triosephosphate isomerase (TIM) has been previously shown to be driven by the global motions of the enzyme, specifically the counter-clockwise rotation of the subunits. In this work, the effect of the substrate dihydroxyacetone phosphate (DHAP) on TIM dynamics is assessed using two apo and two DHAP-bound molecular dynamics (MD) trajectories (each 60 ns long). Multiple events of catalytic loop opening/closure take place during 60 ns runs for both apo TIM and its DHAP-complex. However, counter-clockwise rotation observed in apo TIM is suppressed and bending-type motions are linked to loop dynamics in the presence of DHAP. Bound DHAP molecules also reduce the overall mobility of the enzyme and change the pattern of orientational cross-correlations, mostly those within each subunit. The fluctuations of pseudodihedral angles of the loop 6 residues are enhanced towards the C-terminus, when DHAP is bound at the active site. [ABSTRACT FROM AUTHOR]

Tyrosine nitration is a widespread post-translational modification capable of affecting both the function and structure of the host protein molecule. Enzyme thymidylate synthase (TS), a homodimer, is a molecular target for anticancer therapy. Recently purified TS preparations, isolated from mammalian tissues, were found to be nitrated, suggesting this modification to appear endogenously in normal and tumor tissues. Moreover, human TS (hTS) nitration in vitro led to a by twofold lowered catalytic activity following nitration in average of 1 tyrosine residue per monomer (Dąbrowska-Maś et al. in Org Biomol Chem 10:323-331, 2012), with the modification identified by mass spectrometry at seven different sites (Y33, Y65, Y135, Y213, Y230, Y258 and Y301). In the present paper, combined computational approach, including molecular and essential dynamics and free energy computations, was used to predict the influence on the activity of hTS of nitration of each of the seven tyrosine residues. The simulations were based on the crystal structure of hTS ternary complex with dUMP and Tomudex (PDB code: 1I00), with the Tomudex molecule replaced by the molecule of TS cofactor analogue, tetrahydrofolate. The present results indicate that while with nitration of five out of seven residues (Y33, Y135, Y230, Y258 and Y301), single residue modification appears to have a strong reducing effect on the activity, with the remaining two, Y65 and Y213, no or a weaker influence is apparent. Taken together, these results demonstrate that tyrosine nitrations in the hTS enzyme show clear tendency to influence the structure and dynamics and, in turn, catalytic properties of the host enzyme. These effects are overall distance-dependent. [ABSTRACT FROM AUTHOR]