Environment-dependent long-range structural distortion in a temperature-sensitive point mutant

Authors

  • Jannette Carey,

    Corresponding author
    1. Chemistry Department, Princeton University, Princeton, New Jersey 08544
    • Jannette Carey, Chemistry Department, Princeton University, Princeton, NJ 08544

      Catherine L. Lawson, Department of Chemistry & Chemical Biology, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, NJ 08854

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  • Brian Benoff,

    1. Department of Chemistry & Chemical Biology, Rutgers, The State University of New Jersey, Piscataway New Jersey 08854
    Current affiliation:
    1. Brian Benoff current address is Middletown Board of Education, 900 Nutswamp Road, Middletown, NJ 07748
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  • Balasubramanian Harish,

    1. Chemistry Department, Princeton University, Princeton, New Jersey 08544
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  • Lara Yuan,

    1. Chemistry Department, Princeton University, Princeton, New Jersey 08544
    Current affiliation:
    1. Lara Yuan current address is Boston Biomedical Consultants, 1000 Winter Street, Waltham, MA 02451
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  • Catherine L. Lawson

    Corresponding author
    1. Department of Chemistry & Chemical Biology, Rutgers, The State University of New Jersey, Piscataway New Jersey 08854
    • Jannette Carey, Chemistry Department, Princeton University, Princeton, NJ 08544

      Catherine L. Lawson, Department of Chemistry & Chemical Biology, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, NJ 08854

    Search for more papers by this author

Abstract

Extensive environment-dependent rearrangement of the helix-turn-helix DNA recognition region and adjacent L-tryptophan binding pocket is reported in the crystal structure of dimeric E. coli trp aporepressor with point mutation Leu75Phe. In one of two subunits, the eight residues immediately C-terminal to the mutation are shifted forward in helical register by three positions, and the five following residues form an extrahelical loop accommodating the register shift. In contrast, the second subunit has wildtype-like conformation, as do both subunits in an isomorphous wildtype control structure. Treated together as an ensemble pair, the distorted and wildtype-like conformations of the mutant apoprotein agree more fully than either conformation alone with previously reported NOE measurements, and account more completely for its diverse biochemical and biophysical properties. The register-shifted segment Ile79-Ala80-Thr81-Ile82-Thr83 is helical in both conformations despite low helical propensity, suggesting an important structural role for the steric constraints imposed by β-branched residues in helical conformation.

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