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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 31 (1992), S. 7211-7218 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 34 (1995), S. 7614-7621 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 1935-1942 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The distinct influences of function, folding, and structure on the evolution of minimalist model proteins are studied by characterization of their evolutionary landscapes. Chains of up to 23 monomers on a two-dimensional square lattice are investigated by exhaustive enumeration of conformation and sequence space. In addition to common aspects of minimalist models, such as unique, stable native states and cooperative folding, functional model proteins have the novel feature of an explicit binding pocket. Fitness is defined through simple, physical characterization of the binding pocket. We characterize various properties of functional model proteins, focusing on their evolutionary landscapes, as defined by single point mutations, insertions, and deletions. The longer chains more closely resemble real proteins, having richer functional diversity and forming larger families of sequences. Although regions of evolutionary landscapes are often highly interconnected, we also observe so-called critical pathways, where evolution can only proceed through a single set of mutants. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2846-2847 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In response to Woody and Sreerama's Comment that they have realized significant improvements in calculations of the circular dichroism of proteins over those reported by Hirst previously, we report the simultaneous and independent achievement of comparably accurate calculations. Our calculations are based on parameters from ab initio wave functions, in contrast to the combination of experimental data and semiempirical wave functions used by Woody and Sreerama. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 782-788 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The two most prominent peaks in the far-ultraviolet (UV) circular dichroism (CD) spectra of proteins occur at 190 nm (associated with the ππ* transition) and 220 nm (associated with the nπ* transition). The mean residue ellipticity at 220 nm, [θ]220, is commonly used to estimate the helix content of a protein. We have assessed first principles CD calculations in the far-UV using 23 different proteins, whose x-ray crystal structures and CD spectra are known. Using the standard parameters, derived from semiempirical calculations, for the ground state, nπ* and ππ* electronic states of models of the peptide group to describe the relevant charge distributions of the backbone chromophore, we find weak correlation between the computed and measured mean residue ellipticity at 220 nm (Spearman rank correlation coefficient, r=0.41) and no correlation at 190 nm. Replacing the standard parameters with ones derived from modern quantum chemistry methods (multireference configuration interaction calculations) gives a significant correlation (r=0.62) between the computed and measured [θ]220, but still no correlation at 190 nm. We suggest that further improvements might be expected from a parametrization of the higher energy states of the backbone chromophore, and from a more modern parametrization of side-chain chromophoric groups. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Perspectives in drug discovery and design 1 (1993), S. 279-290 
    ISSN: 1573-9023
    Keywords: Artificial intelligence ; Drug design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Neural networks and machine learning are two methods that are increasingly being used to model QSARs. They make few statistical assumptions and are nonlinear and nonparametric. We describe back-propagation from the field of neural networks, and GOLEM from machine learning, and illustrate their learning mechanisms using a simple expository problem. Back-propagation and GOLEM are then compared with multiple linear regression (using the parameters and their squares) on two real drug design problems: the inhibition ofEscherichia coli dihydrofolate reductase (DHFR) by pyrimidines and the inhibition of rat/mouse tumour DHFR by triazines.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-4951
    Keywords: QSAR ; Artificial intelligence ; Neural networks ; DHFR inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Neural networks and inductive logic programming (ILP) have been compared to linear regression for modelling the QSAR of the inhibition of E. coli dihydrofolate reductase (DHFR) by 2,4-diamino-5-(substitured benzyl)pyrimidines, and, in the subsequent paper [Hirst, J.D., King, R.D. and Sternberg, M.J.E., J. Comput.-Aided Mol. Design, 8 (1994) 421], the inhibition of rodent DHFR by 2,4-diamino-6,6-dimethyl-5-phenyl-dihydrotriazines. Cross-validation trials provide a statistically rigorous assessment of the predictive capabilities of the methods, with training and testing data selected randomly and all the methods developed using identical training data. For the ILP analysis, molecules are represented by attributes other than Hansch parameters. Neural networks and ILP perform better than linear regression using the attribute representation, but the difference is not statistically significant. The major benefit from the ILP analysis is the formulation of understandable rules relating the activity of the inhibitors to their chemical structure.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-4951
    Keywords: QSAR ; Artificial intelligence ; Neural networks ; DHFR inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary One of the largest available data sets for developing a quantitative structure-activity relationship (QSAR) — the inhibition of dihydrofolate reductase (DHFR) by 2,4-diamino-6,6-dimethyl-5-phenyl-dihydrotriazine derivatives — has been used for a sixfold cross-validation trial of neural networks, inductive logic programming (ILP) and linear regression. No statistically significant difference was found between the predictive capabilities of the methods. However, the representation of molecules by attributes, which is integral to the ILP approach, provides understandable rules about drug-receptor interactions.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of computer aided molecular design 12 (1998), S. 563-572 
    ISSN: 1573-4951
    Keywords: anchor points ; conformational search ; ligand binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We compare the low free energy structures of ten small, polar ligands in solution to their conformations in their respective receptor active sites. The solution conformations are generated by a systematic search and the free energies of representative structures are computed with a continuum solvation model. Based on the values of torsion angles, we find little similarity between low energy solution structures of small ligands and their active site conformations. However, in nine out of ten cases, the positions of 'anchor points' (key atoms responsible for tight binding) in the lowest energy solution structures are very similar to the positions of these atoms in the active site conformations. A metric that more closely captures the essentials of binding supports the basic premise underlying pharmacophore mapping, namely that active site conformations of small flexible ligands correspond to their low energy structures in solution. This work supports the efforts of building pharmacophore models based on the information present in solution structures of small isolated ligands.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 1612-1622 
    ISSN: 0192-8651
    Keywords: docking ; energy functions ; simulated annealing ; molecular dynamics ; scoring functions ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A good docking algorithm requires an energy function that is selective, in that it clearly differentiates correctly docked structures from misdocked ones, and that is efficient, meaning that a correctly docked structure can be identified quickly. We assess the selectivity and efficiency of a broad spectrum of energy functions, derived from systematic modifications of the CHARMM param19/toph19 energy function. In particular, we examine the effects of the dielectric constant, the solvation model, the scaling of surface charges, reduction of van der Waals repulsion, and nonbonded cutoffs. Based on an assessment of the energy functions for the docking of five different ligand-receptor complexes, we find that selective energy functions include a variety of distance-dependent dielectric models together with truncation of the nonbonded interactions at 8 Å. We evaluate the docking efficiency, the mean number of docked structures per unit of time, of the more selective energy functions, using a simulated annealing molecular dynamics protocol. The largest improvements in efficiency come from a reduction of van der Waals repulsion and a reduction of surface charges. We note that the most selective potential is quite inefficient, although a hierarchical approach can be employed to take advantage of both selective and efficient energy functions.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 1612-1622, 1998
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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