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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of computer aided molecular design 14 (2000), S. 507-529 
    ISSN: 1573-4951
    Keywords: biomolecular simulation ; drug design ; factor Xa ; GROMOS ; molecular dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Factor Xa is a serine protease which activates thrombin and plays a key regulatory role in the blood-coagulation cascade. Factor Xa is at the crossroads of the extrinsic and intrinsic pathways of coagulation and, hence, has become an important target for the design of anti-thrombotics (inhibitors). It is not known to be involved in other processes than hemostasis and its binding site is different to that of other serine proteases, thus facilitating selective inhibition. The design of high-affinity selective inhibitors of factor Xa requires knowledge of the structural and dynamical characteristics of its active site. The three-dimensional structure of factor Xa was resolved by X-ray crystallography and refined at 2.2 Å resolution by Padmanabhan and collaborators. In this article we present results from molecular dynamics simulations of the catalytic domain of factor Xa in aqueous solution. The simulations were performed to characterise the mobility and flexibility of the residues delimiting the unoccupied binding site of the enzyme, and to determine hydrogen bonding propensities (with protein and with solvent atoms) of those residues in the active site that could interact with a substrate or a potential inhibitor. The simulation data is aimed at facilitating the design of high-affinity selective inhibitors of factor Xa.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of biomolecular NMR 12 (1998), S. 501-508 
    ISSN: 1573-5001
    Keywords: computer simulation ; J-coupling constants ; molecular dynamics ; structure refinement ; time-averaging restraints
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Introducing experimental values as restraints into molecular dynamics (MD) simulations to bias the values of particular molecular properties, such as nuclear Overhauser effect intensities or distances, 3J coupling constants, chemical shifts or crystallographic structure factors, towards experimental values is a widely used structure refinement method. To account for the averaging of experimentally derived quantities inherent in the experimental techniques, time-averaging restraining methods may be used. In the case of structure refinement using 3J coupling constants from NMR experiments, time-averaging methods previously proposed can suffer from large artificially induced structural fluctuations. A modified time-averaged restraining potential energy function is proposed which overcomes this problem. The different possible approaches are compared using stochastic dynamics simulations of antamanide, a cyclic peptide of ten residues.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 26 (1996), S. 66-71 
    ISSN: 0887-3585
    Keywords: BPTI ; folding ; unfolding ; disulfide ; molecular dynamics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The structure and folding of basic pancreatic trypsin inhibitor (BPTI) has been studied extensively by experimental means. We report a computer simulation study of the structural stability of various disulfide mutants of BPTI, involving eight 250-psec molecular dynamics simulations of the proteins in water, with and without a phosphate counterion. The presence of the latter alters the relative stability of the single disulfide species [5-55] and [30-51]. This conclusion can explain results of mutational studies and the conservation of residues in homologues of BPTI, and suggests a possible role of ions in stabilizing one intermediate over another in unfolding or folding processes. © 1996 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 27 (1997), S. 367-384 
    ISSN: 0887-3585
    Keywords: protein folding ; force field ; structure prediction ; molecular dynamics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We present an unusual method for parametrizing low-resolution force fields of the type used for protein structure prediction. Force field parameters were-determined by assigning each a fictitious mass and using a quasi-molecular dynamics algorithm in parameter space. The quasi-energy term favored folded native structures and specifically penalized folded nonnative structures. The force field was generated after optimizing less than 70 adjustable parameters, but shows a strong ability to discriminate between native structures and compact misfolded-alternatives. The functional form of the force field was chosen as in molecular mechanics and is not table-driven. It is continuous with continuous derivatives and is thus suitable for use with algorithms such as energy minimization or newtonian dynamics. Proteins 27:367-384, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 27 (1997), S. 395-404 
    ISSN: 0887-3585
    Keywords: hydration ; solvation ; protein-solvent interactions ; molecular dynamics ; computer simulation ; GROMOS ; SPC water ; radial distribution function ; solvent residence times ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The impact of an extensive, uniform and hydrophobic protein surface on the behavior of the surrounding solvent is investigated. In particular, focus is placed on the possible enhancement of the structure of water at the interface, one model for the hydrophobic effect. Solvent residence times and radial distribution functions are analyzed around three types of atomic sites (methyl, polar, and positively charged sites) in 1 ns molecular dynamics simulations of the α-helical polypeptide SP-C in water, in methanol and in chloroform. For comparison, water residence times at positively and negatively charged sites are obtained from a simulation of a highly charged α-helical polypeptide from the protein titin in water. In the simulations the structure of water is not enhanced at the hydrophobic protein surface, but instead is disrupted and devoid of positional correlation beyond the first solvation sphere. Comparing solvents of different polarity, no clear trend toward the most polar solvent being more ordered is found. In addition, comparison of the water residence times at nonpolar, polar, positively charged, or negatively charged sites on the surface of SP-C or titin does not reveal pronounced or definite differences. It is shown, however, that the local environment may considerably affect solvent residence times. The implications of this work for the interpretation of the hydrophobic effect are discussed. Proteins 27:395-404, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 451-464 
    ISSN: 0887-3585
    Keywords: protein force field ; protein crystal ; protein hydration ; Ca2+ binding site ; molecular dynamics ; subtilisin ; computer simulation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In this paper we present a molecular dynamics (MD) simulation of subtilisin BPN′ in a crystalline environment containing four protein molecules and solvent. Con-formational and dynamic properties of the molecules are compared with each other and with respect to the X-ray structure to test the validity of the force field. The agreement between simulated and experimental structure using the GROMOS force field is better than that obtained in the literature using other force fields for protein crystals. The overall shape of the molecule is well preserved, as is the conformation of α-helices and β-strands. Structural differences are mainly found in loop regions. Solvent networks found in the X-ray structure were reproduced by the simulation, which was unbiased with respect to the crystalline hydration structure. These networks seem to play an important role in the stability of the protein; evidence of this is found in the structure of the active site. The weak ion binding site in the X-ray structure of subtilisin BPN′ is occupied by a monovalent ion. When a calcium ion is placed in the initial structure, three peptide ligands are replaced by 5 water ligands, whereas a potassium ion retains (in part) its original ligands. Existing force fields yield a reliable method to probe local structure and short-time dynamics of proteins, providing an accuracy of about 0.1 nm. © 1992 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 191-195 
    ISSN: 0947-6539
    Keywords: computer simulations ; molecular dynamics ; nucleophilic substitutions ; quantum chemistry ; solvent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvent effects on an SN2 reaction at nitrogen (Cl- + NH2Cl → ClNH2 + Cl-) in dimethyl ether solution were studied by means of molecular dynamics simulation with a combined quantum-chemical and molecular-mechanical potential. The energetics and geometrical parameters of the reaction in the gas phase, calculated by means of the semiempirical model PM3(the quantum chemical part of the combined potential), were compared with ab initio calculations up to the 6-311 + G* */MP2 and 6-311 + G(2 d,p)/MP2 levels of theory. Compared with the gas phase potential energy surface, the free energy profile of the reaction in dimethyl ether solution shows that the solvent makes the ion-dipole complex well shallower by approximately 6.4 kcal mol-1 and raises the height of the effective barrier from the complex to the transition state by about 2.2 kcal mol-1. The overall transition barrier between the separated reactants and the products is raised from 6.4 kcal mol-1 to 15.0 kcal mol-1 upon solvation. The radial distribution functions between solvent-solute atom pairs at different stages of the reaction course were compared. Results show that better solvation of the charge-localised separated reactants is responsible for the increase in the barrier height. Polarisation of the solute by its surroundings is also discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 535-547 
    ISSN: 0192-8651
    Keywords: force field parametrization ; liquid alkanes ; van der Waals interactions ; molecular dynamics ; GROMOS96 ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The derivation of the van der Waals parameters for the aliphatic CHn united atoms of the GROMOS96 force field is presented. The parameters have been adjusted to reproduce the experimental enthalpies of vaporization and vapor pressures or densities of a set of nine alkanes in the liquid state at 298 K (or at the boiling point in the case of methane), using a cutoff radius for the van der Waals interactions of 1.6 nm. Force fields to be used in molecular simulations are bound to the conditions chosen for their parametrization, for example, the temperature, the densities of the systems included in the calibration set, or the cutoff radius used for the nonbonded interactions. Van der Waals parameters for the CHn united atoms of earlier GROMOS force fields were developed using a cutoff radius of 0.8 nm for the van der Waals interactions. Because the van der Waals interaction energy between aliphatic groups separated by distances between 0.8 and 1.4 nm is not negligible at liquid densities, the use of these parameters in combination with longer cutoffs leads to an overestimation of the attractive van der Waals interaction energy. The relevance of this excess attraction depends on the size of the groups that are interacting, as well as on their local densities. Free energies of hydration have been calculated for five alkanes.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 535-547, 1998
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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