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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
    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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  • 3
    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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