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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of computer aided molecular design 13 (1999), S. 243-258 
    ISSN: 1573-4951
    Keywords: binding affinity prediction ; CoMFA ; genetic neural network ; glycogen phosphorylase inhibitor ; QSAR ; structure-based drug design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Finding an accurate method for estimating the affinity of protein ligands activity is the most challenging task in computer-aided molecular design. In this study we investigate and compare seven different prediction methods for a set of 30 glycogen phosphorylase (GP) inhibitors with known crystal structures. Five of the methods involve quantitative structure-activity relationships (QSAR) based on the 2D or 3D structures of the GP ligands alone. They are hologram QSAR (HQSAR), receptor surface model (RSM), comparative molecular field analysis (CoMFA), and applications of genetic neural network to similarity matrix (SM/GNN) or conventional descriptors (C2GNN). All five QSAR-based models have good predictivity and yield q2 values ranging from 0.60 to 0.82. The other two methods, LUDI and a structure-based binding energy predictor (SBEP) system, make use of the structures of the ligand-receptor complexes. The weak correlation between biological activities and the LUDI scores of this set of inhibitors suggests that the LUDI scoring function, by itself, may not be a general method for reliable ranking of a congeneric series of compounds. The SBEP system is derived from a set of physical properties that characterizes ligand-receptor interactions. The final neural network model, which yields a q2 value of 0.60, employs four descriptors. A jury method that combines the predictions of the five QSAR-based models leads to an increase in predictivity. A multi-layer scoring system that utilizes all seven prediction methods is proposed for the evaluation of novel GP ligands.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of computer aided molecular design 14 (2000), S. 161-179 
    ISSN: 1573-4951
    Keywords: de novo design ; finite-difference Poisson–Boltzmann ; HIV-1 aspartic proteinase ; inhibitors of dimerization ; MCSS ; structure-based drug design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Inhibition of dimerization to the active form of the HIV-1 aspartic proteinase (HIV-1 PR) may be a way to decrease the probability of escape mutations for this viral protein. The Multiple Copy Simultaneous Search (MCSS) methodology was used to generate functionality maps for the dimerization interface of HIV-1 PR. The positions of the MCSS minima of 19 organic fragments, once postprocessed to take into account solvation effects, are in good agreement with experimental data on peptides that bind to the interface. The MCSS minima combined with an approach for computational combinatorial ligand design yielded a set of modified HIV-1 PR C-terminal peptides that are similar to known nanomolar inhibitors of HIV-1 PR dimerization. A number of N-substituted 2,5-diketopiperazines are predicted to be potential dimerization inhibitors of HIV-1 PR.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 1-12 
    ISSN: 0887-3585
    Keywords: protein crystallography ; protein refinement ; empirical energy simulations ; error analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The uncertainties in the refined parameters for a 1.5-Å X-ray structure of carbon-monoxy (FeII) myoglobin are estimated by combining energy minimization with least-squares refinement against the X-ray data. The energy minimization, done without reference to the X-ray data, provide perturbed structures which are used to restart conventional X-ray refinement. The resulting refined structures have the same, or better, R-factor and stereochemical parameters as the original X-ray structure, but deviate from it by 0.13 Å rms for the backbone atoms and 0.31 Å rms for the sidechain atoms. Atoms interacting with a disordered sidechain, Arg 45 CD3, are observed to have larger positional uncertainties. The uncertainty in the B-factors, within the isotropic harmonic motion approximation, is estimated to be 15%. The resulting X-ray structures are more consistent with the energy parameters used in simulations.
    Additional Material: 6 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 2 (1987), S. 236-259 
    ISSN: 0887-3585
    Keywords: atomic probability distributions of proteins ; anisotropy and anharmonicity of motions in proteins ; multiple occupancy of atomic positions in proteins ; molecular dynamics simulation ; lysozyme ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Positional probability density functions (pdf) for the atomic fluctuations are determined from a molecular dynamics simulation for hen egg-white lysozyme. Most atoms are found to have motions that are highly anisotropic but only slightly anharmonic. The largest deviations from harmonic motion are in the direction of the largest rms fluctuations in the local principal axis frame. Backbone atoms tend to be more nearly harmonic than sidechain atoms. The atoms with the largest anharmonicities tend to have pdfs with multiple peaks, each of which is close to harmonic. Several model pdfs are evaluated on the basis of how well they fit probability densities from the dynamics simulations when parameterized in terms of the moments of the distribution. Gram-Charlier and Edgeworth perturbation expansions, which have been successful in describing the motions of small molecules in crystals, are shown to be inadequate for the distributions found in the dynamics of proteins. Multipeaked distribution functions are found to be more appropriate.
    Additional Material: 11 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 10 (1991), S. 340-358 
    ISSN: 0887-3585
    Keywords: ribonuclease A ; crambin ; conformational disorder ; protein crystallography ; simulated annealing ; X-ray refinement ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Conformational disorder in crystal structures of ribonuclease-A and crambin is studied by including two independent structures in least-squares optimizations against X-ray data. The optimizations are carried out by X-ray restrained molecular dynamics (simulated annealing refinement) and by conventional least-squares optimization. Starting from two identical structures, the optimizations against X-ray data lead to significant deviations between the two, with rms backbone displacements of 0.45 Å for refinement of ribonuclease at 1.53 Å resolution, and 0.31 Å for crambin at 0.945 Å. More than 15 independent X-ray restrained molecular dynamics runs have been carried out for ribonuclease, and the displacements between the resulting structures are highly reproducible for most atoms. These include residues with two or more conformations with significant dihedral angle differences and alternative hydrogen bonding, as well as groups of residues that undergo displacements that are suggestive of rigid-body librations. The crystallographic R-values obtained are ≈ 13%, as compared to 15.3% for a comparable refinement with a single structure. Least-squares optimization without an intervening restrained molecular dynamics stage is sufficient to reproduce most of the observed displacements. Similar results are obtained for crambin, where the higher resolution of the X-ray data allows for refinement of unconstrained individual anisotropic temperature factors. These are shown to be correlated with the displacements in the two-structure refinements.
    Additional Material: 10 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 11 (1991), S. 205-217 
    ISSN: 0887-3585
    Keywords: molecular dynamics ; normal modes ; collective motions ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A method is described for identifying collective motions in proteins from molecular dynamics trajectories or normal mode simulations. The method makes use of the covariances of atomic positional fluctuations. It is illustrated by an analysis of the bovine pancreatic trypsin inhibitor. Comparison of the covariance and cross-correlation matrices shows that the relative motions have many similar features in the different simulations. Many regions of the protein, especially regions of secondary structure, move in a correlated manner. Anharmonic effects, which are included in the molecular dynamics simulations but not in the normal analysis, are of some importance in determining the larger scale collective motions, but not the more local fluctuations. Comparisons of molecular dynamics simulations in the present and absence of solvent indicate that the environment is of significance for the long-range motions.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 237-265 
    ISSN: 0887-3585
    Keywords: β-sheet-coil transition ; β-hairpin ; Langevin dynamics ; equilibrium properties ; quasiparticle ; effective potential ; autocorrelations ; cross-correlations ; time histories ; rate constants ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A simplified model of a polypeptide chain is used to study the dynamics of the β-sheet-coil transition. Each amino acid residue is treated as a single quasiparticle in an effective potential that approximates the potential of mean force in solution. The model is used to study the equilibrium and dynamic aspects of the sheet-coil transition. Systems studied include ones with both strands free to move (two-strand sheet), and ones with either strand fixed in position (multistrand sheet). The equilibrium properties examined include sheet-coil equilibrium constants and their dependence on chain position. Dynamic properties are investigated by a stochastic simulation of the Brownian motion of the chain in its solvent surroundings. Time histories of the dihedral angles and residue-residue cross-strand distances are used to study the behavior of the sheet structure. Auto-and cross-correlation functions are calculated from the time histories with relaxation times of tens to hundreds of picoseconds. Sheet-coil rate constants of tens of ns-1 were found for the fixed strand cases.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 199-221 
    ISSN: 0887-3585
    Keywords: multicopy simulation search ; rational drug design ; database search ; computer-aided design ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A program (HOOK) is described for generating potential ligands that satisfy the chemical and steric requirements of the binding region of a macromolecule. Functional group sites with defined positions and orientations are derived from known ligand structures or the multicopy simulation search (MCSS) method (Miranker, A., Karplus, M. Proteins 11:29-34, 1991). HOOK places molecular “skeletons” from a database into the protein binding region by making bonds between sites (“hooks”) on the skeleton and functional groups. The nonpolar interactions with the binding region of candidate molecules are assessed by use of a simplified van der Waals potential. The method is illustrated by constructing ligands for the sialic acid binding site of the hemagglutinin from the influenza A virus and the active site of chloramphenicol acetyltransferase. Aspects of the HOOK program that lead to a highly efficient search of 105 or more skeletons for binding to 102 or more functional group minima are outlined. © 1994 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 23 (1995), S. 12-31 
    ISSN: 0887-3585
    Keywords: molecular dynamics ; electrostatics ; carboxypeptidase A ; carbonic anhydrase ; zinc ion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Force field parameters that use a combination of Lennard-Jones and electrostatic interactions are developed for divalent zinc and tested in solution and protein simulations. It is shown that the parameter set gives free energies of solution in good agreement with experiment. Molecular dynamics simulations of carboxypeptidase A and carbonic anhydrase are performed with these zinc parameters and the CHARMM 22 β all-atom parameter set. The structural results are as accurate as those obtained in published simulations that use specifically bonded models for the zinc ion and the AMBER force field. The inclusion of longer-range electrostatic interactions by use of the Extended Electrostatics model is found to improve the equilibrium conformation of the active site. It is concluded that the present parameter set, which permits different coordination geometries and ligand exchange for the zinc ion, can be employed effectively for both solution and protein simulations of zinc-containing systems. © 1995 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 4 (1988), S. 148-156 
    ISSN: 0887-3585
    Keywords: Protein structure ; empirical energy ; energy minimization ; molecular dynamics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A method for the prediction of hydrogen positions in proteins is presented. The method is based on the knowledge of the heavy atom positions obtained, for instance, from X-ray crystallography. It employs an energy minimization limited to the environment of the hydrogen atoms bound to a common heavy atom or to a single water molecule. The method is not restricted to proteins and can be applied without modification to nonpolar hydrogens and to nucleic acids. The method has been applied to the neutron diffraction structures of trypsin ribonuclease A, and bovine pancreatic trypsin inhibitor. A comparison of the constructed and the observed hydrogen positions shows few deviations except in situations in which several energetically similar conformations are possible. Analysis of the potential energy of rotation of Lys amino and Ser, Thr, Tyr hydroxyl groups reveals that the conformations of lowest intrinsic torsion energies are statistically favored in both the crystal and the constructed structures.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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