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

Protein Sci. 2012 Jan;21(1):63-74. doi: 10.1002/pro.759. Epub 2011 Dec 8.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Apoproteins / chemistry*
  • Apoproteins / genetics*
  • Apoproteins / metabolism
  • Bacterial Proteins
  • Binding Sites
  • DNA / chemistry
  • DNA / metabolism
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / genetics*
  • Escherichia coli Proteins / metabolism
  • Hydrophobic and Hydrophilic Interactions
  • Models, Molecular
  • Molecular Sequence Data
  • Nuclear Magnetic Resonance, Biomolecular
  • Point Mutation*
  • Repressor Proteins / chemistry*
  • Repressor Proteins / genetics*
  • Repressor Proteins / metabolism
  • Structure-Activity Relationship
  • Temperature

Substances

  • Apoproteins
  • Bacterial Proteins
  • Escherichia coli Proteins
  • Repressor Proteins
  • TRPR protein, E coli
  • DNA