Strengthened arm-dimerization domain interactions in AraC

J Biol Chem. 2001 Jan 26;276(4):2562-4. doi: 10.1074/jbc.M008705200. Epub 2000 Nov 7.

Abstract

Constitutive mutations were sought and found in the N-terminal arm of the Escherichia coli regulatory protein of the arabinose operon, AraC protein. A new mutation, N16D, was of particular interest. Asn-16 is not seen in the crystal structure of the AraC dimerization domain determined in the absence of arabinose, because the N-terminal arm 18 residues are disordered, but in the presence of arabinose, residues 7-18 fold over the arabinose and make many interactions with it. In this state Asn-16 lies near two positively charged amino acids, Lys-43 and Arg-99. We propose that the introduction of the negatively charged aspartic residue at position 16 creates a charge-charge interaction network among Asp-16, Lys-43, and Arg-99 that holds the arm to the dimerization domain even in the absence of arabinose. This frees the DNA-binding domains and allows them to bind cis to I(1)-I(2) half-sites and activate transcription. Mutating the two positively charged residues to alanines individually and collectively decreased or eliminated the constitutivity created by the N16D mutation.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • AraC Transcription Factor
  • Arabinose / metabolism*
  • Arginine
  • Aspartic Acid
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Dimerization
  • Escherichia coli Proteins
  • Gene Expression Regulation, Bacterial*
  • Lysine
  • Models, Genetic
  • Mutation
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Transcription Factors*

Substances

  • AraC Transcription Factor
  • AraC protein, E coli
  • Bacterial Proteins
  • Escherichia coli Proteins
  • Repressor Proteins
  • Transcription Factors
  • Aspartic Acid
  • Arginine
  • Arabinose
  • Lysine