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CAMM techniques for the prediction of the mechanical properties of tendons and ligaments nanostructures.

Theoretical prediction of the mechanical properties of soft tissues usually relies on a top-down approach; that is analysis is gradually refined to observe smaller structures and properties until technical limits are reached. Computer-Assisted Molecular Modeling (CAMM) allows for the reversal of this approach and the performance of bottom-up modeling instead. The wealth of available sequences and structures provides an enormous database for computational efforts to predict structures, simulate docking and folding processes, simulate molecular interactions, and understand them in quantitative energetic terms. Tendons and ligaments can be considered an ideal arena due to their well defined and highly organized architecture which involves not only the main structural constituent, the collagen molecule, but also other important molecular "actors" such as proteoglycans and glycosaminoglycans. In this ideal arena each structure is well organized and recognizable, and using the molecular modeling tool it is possible to evaluate their mutual interactions and to characterize their mechanical function. Knowledge of these relationships can be useful in understanding connective tissue performance as a result of the cooperation and mutual interaction between different biological structures at the nanoscale.

Algorithms↗

Prediction of HIV-1 protease inhibitor resistance using a protein-inhibitor flexible docking approach.

Emergence of drug resistance remains one of the most challenging issues in the treatment of HIV-1 infection. Here we focus on resistance to HIV-1 protease inhibitors (PIs) at a molecular level, which can be analysed genotypically or phenotypically. Genotypic assays are based on the analysis of mutations associated with reduced drug susceptibility, but are problematic because of the numerous mutations and mutational patterns that confer drug resistance. Phenotypic resistance or susceptibility can be experimentally evaluated by measuring the amount of free drug bound to HIV-1 protease molecules, but this procedure is expensive and time-consuming. To overcome these problems, we have developed a docking protocol that takes protein-inhibitor flexibility into account to predict phenotypic drug resistance. For six FDA-approved Pls and a total of 1792 HIV-1 protease sequence mutants, we used a combination of inhibitor flexible docking and molecular dynamics (MD) simulations to calculate protein-inhibitor binding energies. Prediction results were expressed as fold changes of the calculated inhibitory constant (Ki), and the samples predicted to have fold-increase in calculated Ki above the fixed cut-off were defined as drug resistant. Our combined docking and MD protocol achieved accuracies ranging from 72-83% in predicting resistance/susceptibility for five of the six drugs evaluated. Evaluating the method only on samples where our predictions concurred with established knowledge-based methods resulted in increased accuracies of 83-94% for the six drugs. The results suggest that a physics-based approach, which is readily applicable to any novel PI and/or mutant, can be used judiciously with knowledge-based approaches that require experimental training data to devise accurate models of HIV-1 Pl resistance prediction.

Binding Sites↗

A possible molecular mechanism of hanatoxin binding-modified gating in voltage-gated K+-channels.

While S4 is known as the voltage sensor in voltage-gated potassium channels, the carboxyl terminus of S3 (S3C) is of particular interest concerning the site for gating modifier toxins like hanatoxin. The thus derived helical secondary structural arrangement for S3C, as well as its surrounding environment, has since been intensively and vigorously debated. Our previous structural analysis based on molecular simulation has provided sufficient information to describe reasonable docking conformation and further experimental designs (Lou et al., 2002. J. Mol. Recognit. 15: 175-179). However, if one only relies on such information, more advanced structure-functional interpretations for the roles S3C may play in the modification of gating behavior upon toxin binding will remain unknown. In order to have better understanding of the molecular details regarding this issue, we have performed the docking simulation with the S3C sequence from the hanatoxin-insensitive K+-channel, shaker, and analyzed the conformational changes resulting from such docking. Compared with other functional data from previous studies with respect to the proximity of the S3-S4 linker region, we suggested a significant movement of drk1 S3C, but not shaker S3C, in the direction presumably towards S4, which was comprehended as a possible factor interfering with S4 translocation during drk1 gating in the presence of toxin. In combination with the discussions for structural roles of the length of the S3-S4 linker, a possible molecular mechanism to illustrate the hanatoxin binding-modified gating is proposed.

Binding Sites↗

Construction of a 3D model of nattokinase, a novel fibrinolytic enzyme from Bacillus natto. A novel nucleophilic catalytic mechanism for nattokinase.

A three-dimensional structural model of nattokinase (NK) from Bacillus natto was constructed by homology modeling. High-resolution X-ray structures of Subtilisin BPN' (SB), Subtilisin Carlsberg (SC), Subtilisin E (SE) and Subtilisin Savinase (SS), four proteins with sequential, structural and functional homology were used as templates. Initial models of NK were built by MODELLER and analyzed by the PROCHECK programs. The best quality model was chosen for further refinement by constrained molecular dynamics simulations. The overall quality of the refined model was evaluated. The refined model NKC1 was analyzed by different protein analysis programs including PROCHECK for the evaluation of Ramachandran plot quality, PROSA for testing interaction energies and WHATIF for the calculation of packing quality. This structure was found to be satisfactory and also stable at room temperature as demonstrated by a 300ps long unconstrained molecular dynamics (MD) simulation. Further docking analysis promoted the coming of a new nucleophilic catalytic mechanism for NK, which is induced by attacking of hydroxyl rich in catalytic environment and locating of S221.

Amino Acid Sequence↗

Improved prediction of HIV-1 protease-inhibitor binding energies by molecular dynamics simulations.

BACKGROUND: The accurate prediction of enzyme-substrate interaction energies is one of the major challenges in computational biology. This study describes the improvement of protein-ligand binding energy prediction by incorporating protein flexibility through the use of molecular dynamics (MD) simulations. RESULTS: Docking experiments were undertaken using the program AutoDock for twenty-five HIV-1 protease-inhibitor complexes determined by x-ray crystallography. Protein-rigid docking without any dynamics produced a low correlation of 0.38 between the experimental and calculated binding energies. Correlations improved significantly for all time scales of MD simulations of the receptor-ligand complex. The highest correlation coefficient of 0.87 between the experimental and calculated energies was obtained after 0.1 picoseconds of dynamics simulation. CONCLUSION: Our results indicate that relaxation of protein complexes by MD simulation is useful and necessary to obtain binding energies that are representative of the experimentally determined values.

Computer Simulation↗

Antagonist and agonist binding models of the human gonadotropin-releasing hormone receptor.

G-protein-coupled receptors (GPCRs) constitute one of the most important classes of drug targets. Since the first high-resolution structure of a GPCR was determined by Palczewski and co-workers [K. Palczewski, T. Kumasaka, T. Hori, C.A. Behnke, H. Motoshima, B.A. Fox, I. Le Trong, D.C. Teller, T. Okada, R.E. Stenkamp, M. Yamamoto, M. Miyano, Crystal structure of rhodopsin: a G-protein-coupled receptor, Science 289 (2000) 739-745], development of in silico models of rhodopsin-like GPCRs could be rationally founded. In this work, we present a model of the human gonadotropin-releasing hormone receptor based on the rhodopsin structure. The transmembrane helices are modeled by homology, while the extra- and intra-cellular loops are modeled in such a way that experimentally determined interactions and microdomains (e.g., hydrophobic cores) are retained. We conclude that specifically tailored models, compared to more automatic approaches, have the benefit that known interactions are easily introduced early in the homology modeling. Furthermore, tailored models, although more tedious to construct, are better suited for drug lead finding and for compound optimization. To test the stability of the receptor, we performed a 1 ns molecular dynamics simulation. Moreover, we docked two agonists (native GnRH and Triptorelin, [dTrp(6)]-GnRH) and two antagonists (Cetrorelix, dNal(1)-dCpa(2)-dPal(3)-Ser(4)-Tyr(5)-dCit(6)-Leu(7)-Arg(8)-Pro(9)-dAla(10)), and the covalently constrained dicyclic decapeptide dicyclo(1,1'-5/4-10)[Ac-Glu(1)(Gly(1)')-dCpa(2)-dTrp(3)-Asp(4)-dbu(5)-dNal(6)-Leu(7)-Arg(8)-Pro(9)-dpr(10)-NH(2)] into the putative receptor binding site. The docked ligand conformations result in ligand-receptor interactions that are generally in good agreement with site-directed mutagenesis and ligand-binding studies presented in the literature. Our results indicate that the binding conformation of the antagonists differs from that of the agonists. This difference can be linked to the activation or inhibition of the receptor.

Binding Sites↗

Calpha-H...O = C hydrogen bonds contribute to the specificity of RGD cell-adhesion interactions.

BACKGROUND: The Arg-Gly-Asp (RGD) cell adhesion sequence occurs in several extracellular matrix molecules known to interact with integrin cell-surface receptors. Recently published crystal structures of the extracellular regions of two integrins in complex with peptides containing or mimicking the RGD sequence have identified the Arg and Asp residues as key specificity determinants for integrin recognition, through hydrogen bonding and metal coordination interactions. The central Gly residue also appears to be in close contact with the integrin surface in these structures. RESULTS: When hydrogen atoms are modelled on the central Gly residue with standard stereochemistry, the interaction between this residue and a carbonyl group in the integrin surface shows all the hallmarks of Calpha-H...O = C hydrogen bonding, as seen in the collagen triple helix and in many crystal structures of small organic molecules. Moreover, molecular dynamic simulations of the docking of RGD-containing fragments on integrin surfaces support the occurrence of these interactions. There appears to be an array of four weak and conventional hydrogen bonds lining up the RGD residues with main chain carbonyl groups in the integrin surface. CONCLUSIONS: The occurrence of weak Calpha-H...O = C hydrogen bonds in the RGD-integrin interaction highlights the importance of the conserved Gly residue in the RGD motif and its contribution to integrin-ligand binding specificity. Our analysis shows how weak hydrogen bonds may also play important biological roles by contributing to the specificity of macromolecular recognition.

Arginine↗

Development and validation of empirical force field parameters for netropsin.

The netropsin molecule preferentially binds to the four consecutive A.T base pairs of the DNA minor groove and could therefore inhibit the expression of specific genes. The understanding of its binding on a molecular level is indispensable for computer-aided design of new antitumor agents. This knowledge could be obtained via molecular dynamics (MD) and docking simulations, but in this case appropriate force field parameters for the netropsin molecule should be explicitly defined. Our parametrization was based on the results of quantum chemical calculations. The resulting set of parameters was able to reproduce bond lengths, bond angles, torsional angles of the ab initio minimized geometry within 0.03 A, 3 deg and 5 deg, respectively, and its vibrational frequencies with a relative error of 4.3% for low and 2.8% for high energy modes. To show the accuracy of the developed parameters we calculated an IR spectrum of the netropsin molecule using MD simulation and found it to be in good agreement with the experimental one. Finally, we performed a 10 ns long MD simulation of the netropsin-DNA complex immersed in explicit water. The overall complex conformation remained stable at all times, and its secondary structure was well retained.

Algorithms↗

Exploring the recognized bio-mimicry materials for gas sensing.

This study was undertaken to synthesize peptides that are partially similar to the binding sites of human olfactory receptor protein. First, a putative 3-D model structure of human olfactory receptor protein (P30953) was modeled using a molecular simulation method. The computer docking simulation was then performed to determine the most plausible binding sites between the model structure and target gases, trimethylamine, ammonia, acetic acid, and o-xylene. According to the simulation result, a series of polypeptide sequences, horp61 for TMA, horp103 for o-xylene, horp109 for ammonia, and horp193 for acetic acid as recognized molecules were designed for gas sensing purposes. Preparing these peptides as corresponding gas sensing probes, the results showed a high relative sensitivity response of 6.7 for TMA (probe horp61), 5.1 for o-xylene (probe horp103), 11 for ammonia (probe horp109), and 28 for acetic acid (probe horp193), respectively. These results indicate that peptide mimicking of binding domain on olfactory receptor opens a new window and offers a novel strategy for the further development of recognized materials for gas sensing.

Amino Acid Sequence↗

Minimal structural elements of an inhibitory anti-ATF1/CREB single-chain antibody fragment (scFv41.4).

Antibody variable domains represent potential structural models for the rational design of therapeutic molecules that bind cellular proteins with high affinity and specificity. The Activating Transcription Factor 1 (ATF1)/Cyclic AMP Response Element Binding Protein (CREB) family of transcription factors are particularly relevant targets due to their strong association with melanoma and clear cell sarcoma. Biochemical and structural investigations were performed to optimize a single-chain antibody fragment (scFv), scFv41.4, that disrupts the binding of ATF1/CREB to cyclic-AMP response elements (CRE) in vitro and inhibits transcriptional activation in cells. Molecular modeling and ligand docking simulations suggested that scFv41.4 could function as a disulfide-deficient single domain scFv. Functional studies verified that deletion of the light chain did not result in reduced inhibitory activity. The isolated heavy chain was predicted to assume a relaxed structural conformation that maintained a functional antigen binding pocket. The minimal structural elements necessary for intracellular function were further analyzed by selective deletion of CDR1 and CDR2. V(H)-CDR1 and V(H)-CDR3 were shown to play a key role in antigen binding activity, but V(H)-CDR2 was dispensable. Thus, scFv41.4 represents a unique molecule with potential for use in the design of peptidomimetic derivatives having therapeutic application to human cancer.

Activating Transcription Factor 1↗

Engineering the substrate specificity of D-amino-acid oxidase.

The high resolution crystal structure of D-amino-acid oxidase (DAAO) from the yeast Rhodotorula gracilis provided us with the tool to engineer the substrate specificity of this flavo-oxidase. DAAO catalyzes the oxidative deamination of D-amino acids, with the exception of D-aspartate and D-glutamate (which are oxidized by D-aspartate oxidase, DASPO). Following sequence homology, molecular modeling, and simulated annealing docking analyses, the active site residue Met-213 was mutated to arginine. The mutant enzyme showed properties close to those of DASPO (e.g. the oxidation of D-aspartate and the binding of l-tartrate), and it was still active on D-alanine. The presence of an additional guanidinium group in the active site of the DAAO mutant allowed the binding (and thus the oxidation) of D-aspartate, but it was also responsible for a lower catalytic activity on D-alanine. Similar results were also obtained when two additional arginines were simultaneously introduced in the active site of DAAO (M213R/Y238R mutant, yielding an architecture of the active site more similar to that obtained for the DASPO model), but the double mutant showed very low stability in solution. The decrease in maximal activity observed with these DAAO mutants could be due to alterations in the precise orbital alignment required for efficient catalysis, although even the change in the redox properties (more evident in the DAAO-benzoate complex) could play a role. The rational design approach was successful in producing an enzymatic activity with a new, broader substrate specificity, and this approach could also be used to develop DAAO variants suitable for use in biotechnological applications.

Binding Sites↗

Monte Carlo docking simulations of cyclomaltoheptaose and dimethyl cyclomaltoheptaose with paclitaxel.

The molecular basis for the remarkable enhancement of the solubility of paclitaxel by O-dimethylcyclomaltoheptaose (DM-beta-CD) over cyclomaltoheptaose (beta-cyclodextrin, beta-CD) was investigated with Monte Carlo docking-minimization simulation. As possible guests of inclusion complexation for the host cyclic oligosaccharides, two functional moieties of the suggested solution structure of paclitaxel were used where one is the C-3'N benzoyl moiety (B-ring) and the other is a hydrophobic (HP) cluster site among the C-3' phenyl (C-ring), C-2 benzoate (A-ring), and C-4 acetoxy moieties. The energetic preference of inclusion complexation of DM-beta-CD over beta-CD was analyzed on the basis of more efficient partitioning process of DM-beta-CD into the hydrophobic cluster site of the paclitaxel.

Antineoplastic Agents, Phytogenic↗

Exploring the active-site of a rationally redesigned lipase for catalysis of Michael-type additions.

Michael-type additions of various thiols and alpha,beta-unsaturated carbonyl compounds were performed in organic solvent catalyzed by wild-type and a rationally redesigned mutant of Candida antarctica lipase B. The mutant lacks the nucleophilic serine 105 in the active-site; this results in a changed catalytic mechanism of the enzyme. The possibility of utilizing this mutant for Michael-type additions was initially explored by quantum-chemical calculations on the reaction between acrolein and methanethiol in a model system. The model system was constructed on the basis of docking and molecular-dynamics simulations and was designed to simulate the catalytic properties of the active site. The catalytic system was explored experimentally with a range of different substrates. The kca values were found to be in the range of 10(-3) to 4 min(-1), similar to the values obtained with aldolase antibodies. The enzyme proficiency was 10(7). Furthermore, the Michael-type reactions followed saturation kinetics and were confirmed to take place in the enzyme active site.

Binding Sites↗

Does tetracycline bind helix 2 of prion? An integrated spectroscopical and computational study of the interaction between the antibiotic and alpha helix 2 human prion protein fragments.

We demonstrate here that tetracycline (TC) can strongly interact (KD' = 189 +/- 7 nM) with model peptides derived from the C-terminal globular domain of the prion protein, hPrP [173-195], and that interaction concerns residues within the C-terminal half of the helix 2, a short region previously indicated as endowed with ambivalent conformational behavior and implicated in PrP conversion to the beta-sheet-rich, infective scrapie variant. Data have been confirmed by binding studies with the N-terminal truncated 180-195 variant that displays a dissociation constant of 483 +/- 30 nM. Remarkably, TC does not influence the structure of the N-terminally fluoresceinated peptides that both show alpha-helical conformations. Docking calculations and molecular dynamics simulations suggest a direct, strong interaction of the antibiotic with exposed side chain functional groups of threonines 190-193 on the solvent-exposed surface of helix 2.

Amino Acid Sequence↗

Rational design of a lipase to accommodate catalysis of Baeyer-Villiger oxidation with hydrogen peroxide.

The mechanism and potential energy surface for the Baeyer-Villiger oxidation of acetone with hydrogen peroxide catalyzed by a Ser105-Ala mutant of Candida antarctica Lipase B has been determined using ab initio and density functional theories. Initial substrate binding has been studied using an automated docking procedure and molecular dynamics simulations. Substrates were found to bind to the active site of the mutant. The activation energy for the first step of the reaction, the nucleophilic attack of hydrogen peroxide on the carbonyl carbon of hydrogen peroxide, was calculated to be 4.4 kcal x mol(-1) at the B3LYP/6-31+G* level. The second step, involving the migration of the alkyl group, was found to be the rate-determining step with a computed activation energy of 19.9 kcal x mol(-1) relative the reactant complex. Both steps were found to be lowered considerably in the reaction catalyzed by the mutated lipase, compared to the uncatalyzed reaction. The first step was lowered by 36.0 kcal x mol(-1) and the second step by 19.5 kcal x mol(-1). The second step of the reaction, the rearrangement step, has a high barrier of 27.7 kcal x mol(-1) relative to the Criegee intermediate. This could lead to an accumulation of the intermediate. It is not clear whether this result is an artifact of the computational procedure, or an indication that further mutations of the active site are required. Figure Second TS (18TS) in the Baeyer-Villiger oxidation in a mutant of CALB. Distances in A

Binding Sites↗

Molecular recognition between 4a S/R-galanthamine diastereoisomers and alpha-cyclodextrin.

Molecular recognition between 4a S/R-galanthamine diastereoisomers (1: 4a S-galanthamine;2: 4a R-galanthamine) and alpha-cyclodextrin (alpha-CD) were studied by use of docking and molecular dynamics (MD) simulation approaches. The binding energy of constructed 2...alpha-CD complexes is approximately 17 kcal mol(-1) lower than that of 1...alpha-CD, implying a stronger binding ability of 2 with alpha-CD than that of1. The theoretical modeling result is consistent with our previous CZE result, which demonstrated that alpha-CD is an efficient chiral additive for separating 1 and 2. The modeling result also indicates that both hydrophobic interaction and H-bond force may work as major factors for molecular recognition between the galanthamine diastereoisomers and alpha-CD.

Computer Simulation↗

Computational studies of H5N1 hemagglutinin binding with SA-alpha-2, 3-Gal and SA-alpha-2, 6-Gal.

For influenza H5N1 hemagglutinin, a switch from SA-alpha-2, 3-Gal to SA-alpha-2, 6-Gal receptor specificity is a critical step leading to the conversion from avian-to-human to human-to-human infection. Therefore, the understanding of the binding modes of SA-alpha-2, 3-Gal and SA-alpha-2, 6-Gal to H5N1 hemagglutinin will be very important for the examination of possible mutations needed for going from an avian to a human flu virus. Based on the available H5N1 hemagglutinin crystal structure, the binding profiles between H5N1 hemagglutinin and two saccharide ligands, SA-alpha-2, 3-Gal and SA-alpha-2, 6-Gal, were investigated by ab initio quantum mechanics, molecular docking, molecular mechanics, and molecular dynamics simulations. It was found that SA-alpha-2, 3-Gal has strong multiple hydrophobic and hydrogen bond interactions in its trans conformation with H5N1 hemagglutinin, whereas the SA-alpha-2, 6-Gal only shows weak interactions in a different conformation (cis type).

Computational Biology↗

Identifying inhibitors of the SARS coronavirus proteinase.

The Severe Acute Respiratory Syndrome (SARS) is a serious respiratory illness that has recently been reported in parts of Asia and Canada. In this study, we use molecular dynamics (MD) simulations and docking techniques to screen 29 approved and experimental drugs against the theoretical model of the SARS CoV proteinase as well as the experimental structure of the transmissible gastroenteritis virus (TGEV) proteinase. Our predictions indicate that existing HIV-1 protease inhibitors, L-700,417 for instance, have high binding affinities and may provide good starting points for designing SARS CoV proteinase inhibitors.

Antiviral Agents↗