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  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure and internal motions of the protein hen egg white lysozyme are studied by analysis of simulation and experimental data. A molecular dynamics simulation and an energy minimization of the protein in vacuum have been made and the results compared with high-resolution structures and temperature factors of hen egg white lysozyme in two different crystal forms and of the homologous protein human lysozyme. The structures obtained from molecular dynamics and energy minimization have root-mean-square deviations for backbone atoms of 2.3 Å and 1.1-1.3 Å, respectively, relative to the crystal structures; the different crystal structures have root-mean-square deviations of 0.73-0.81 Å for the backbone atoms. In comparing the backbone dihedral angles, the difference between the dynamics and the crystal structure on which it is based is the same as that between any two crystal structures. The internal fluctuations of atomic positions calculated from the molecular dynamics trajectory agree well with the temperature factors from the three structures. Simulation and crystal results both show that there are large motions for residues involved in exposed turns of the backbone chain, relatively smaller motions for residues involved in the middle of helices or β-sheet structures, and relatively small motions of residues near disulfide bridges. Also, both the simulation and crystal data show that side-chain atoms have larger fluctuations than main-chain atoms. Moreover, the regions that have large deviations among the x-ray crystal structures, which indicates flexibility, are found to have large fluctuations in the simulation.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 645-677 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular and harmonic dynamics simulations have been performed for a decaglycine α-helix. The extent of anharmonicity for various observables is studied by a direct comparison of the two types of simulations, at temperatures ranging from 5 to 300 K. The fluctuations of the cartesian, internal and normal mode coordinates, and their time dependence, are analyzed. The heat capacity of the α-helix is evaluated both from the temperature response of the system to an energy perturbation and from the fluctuations in the temperature of the system. It is shown that the anharmonicity depends on the kind of observable. The root mean square atomic fluctuations have significant anharmonic components at temperatures above 100 K. In contrast, the dihedral angle fluctuations are much closer to being harmonic at all the temperatures considered. The analysis of potentials of mean force experienced by individual atoms shows that atomic displacements have approximately Gaussian distributions from 50 to 300 K, with different force constants at each temperature (quasi-harmonic model). At 300 K, the force constants obtained by molecular dynamics are significantly lower than in the harmonic case. The time dependence of the projection of the molecular dynamics displacements on the normal mode coordinates shows that mode mixing is important above 100 K. The motions of the helix associated with the low-frequency normal modes are described and illustrated.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 19 (1980), S. 2033-2045 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simplified model of a polypeptide chain is described. Each residue is represented by a single interaction center. The energy of the chain and the force acting on each residue are given as a function of the residue coordinates. Terms to approximate the effect of solvent and the stabilization energy of helix formation are included. The model is used to study equilibrium and dynamical aspects of the helix-coil transition. The equilibrium properties examined include helix-coil equilibrium constants and their dependence on chain position. Dynamical properties are examined by a stochastic simulation of the Brownian motion of the chain in its solvent surroundings. Correlations in the motions of the residues are found to have an important influence on the helix-coil transition rates.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 24 (1985), S. 843-865 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stochastic boundary molecular-dynamics approach for studying chemical events in liquids is extended to proteins. A method for simulating the localized dynamics of a portion of a protein is developed and illustrated by an application to the bovine pancreatic trypsin inhibitor (BPTI). The dynamics of the aromatic ring atoms of Tyr 21 of BPTI are targeted as the “active site,” and the results from several different localized models are compared with those from a simulation of the entire molecule. The most consistent results are obtained with a model that consists of a buffer region composed of harmonically constrained Langevin atoms surrounding the active site region whose atoms are treated by molecular dynamics. Possible applications of the model are discussed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 19 (1980), S. 1375-1405 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dynamics of activated rotations of a tyrosine ring inside the bovine pancreatic trypsin inhibitor have been studied by computer simulation. The simulation method consists of two parts. In the first part, typical transition-state configurations of the protein atoms are prepared. In the second part, the classical equations of motion for the protein atoms are solved to yield trajectories which pass through these transition-state configurations. Analysis of the trajectories shows that the ring is driven over the rotational potential barrier by nearly impulsive collisions with atoms of the surrounding protein matrix. The collisions are similar to those that occur while the ring oscillates about its equilibrium orientation. The frequency and strength of the collisions are such that transition-state theory is approximately valid for this simple reaction. The enthalpy of activation is substantially reduced by bond-angle deformations which occur rapidly on the time scale of the barrier crossing. Small, transient packing defects in the protein appear to play a role in initiating the ring rotation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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