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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 297-313 
    ISSN: 0887-3585
    Keywords: information theory ; entropy ; variability ; sequence comparison ; immunoglobulins ; antibodies ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We propose the use of the information-theoretical entropy, S = -Σpi log2 Pi, as a measure of variability at a given position in a set of aligned sequences. pi stands for the fraction of times the i-th type appears at a position. For protein sequences, the sum has up to 20 terms, for nucleotide sequences, up to 4 terms, and for codon sequences, up to 61 terms. We compare S and VS, a related measure, in detail with VK, the traditional measure of immunoglobulin sequence variability, both in the abstract and as applied to the immunoglobulins. We conclude that S has desirable mathematical properties that VK lacks and has intuitive and statistical meanings that accord well with the notion of variability. We find that VK and the S-based measures are highly correlated for the immunoglobulins. We show by analysis of sequence data and by means of a mathematical model that this correlation is due to a strong tendency for the frequency of occurrence of amino acid types at a given position to be log-linear. It is not known whether the immunoglobulins are typical or atypical of protein families in this regard, nor is the origin of the observed rank-frequency distribution obvious, although we discuss several possible etiologies.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 797-808 
    ISSN: 0192-8651
    Keywords: van der Waals surface area (vdWSA) ; solvent-accessible surface area (SASA), numerical calculation ; neighbor list ; united- and all-atom representations ; protein structures ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A general, fast, and exact optimization, called neighbor-list reduction (NLR), is presented, which can be used to accelerate the computation of hard-sphere molecular surface areas. NLR allows selected neighbors of a central atom to be removed from the computation in a preprocessing step, thus allowing the calculation of the atom's surface area to proceed with a shorter list of neighbors. The atoms removed are those having intersections with the central atom falling entirely within unions of other atoms' intersections with the central atom. We describe explicit methods for two levels of neighbor-list reduction: 3NLR considers three hard spheres at a time - the central atom, the candidate for removal, and one other neighbor; whereas 4NLR considers two other neighbors. We demonstrate the correctness and efficiency of this optimization by means of a modified version of the NACCESS program, which computes atomic and molecular surface areas numerically. As test cases we used compounds of different size and class, with and without explicit hydrogens. When van der Waals surface (vdWSA) is computed, the NLR methods reduce the length of the neighbor list by as much as 41%; when solvent-accessible surface area (SASA) is computed, the reduction is as great as 74%. The overall speed improvement due to these reductions is a factor of only about 1.2 for vdWSA, but is about 2.0 for the computation of SASA, in the context of this particular program. All 39,554 calculated atomic surface areas (vdWSA and SASA) were found to be identical to within 0.001 Å2 to those obtained without NLR.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 797-808, 1998
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 1110-1110 
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: No abstract.
    Type of Medium: Electronic Resource
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