Aspartate receptors of Escherichia coli and Salmonella typhimurium bind ligand with negative and half-of-the-sites cooperativity

Biochemistry. 1994 Jan 25;33(3):629-34. doi: 10.1021/bi00169a002.

Abstract

The aspartate receptors of Escherichia coli and Salmonella typhimurium which mediate chemotactic responsiveness to aspartate have 79% amino acid sequence identity but exhibited apparently quite different aspartate binding plots. The Scatchard plot of the Salmonella receptor was concave upward whereas the E. coli receptor gave a straight line. Because the two binding sites in the Salmonella receptor lacking aspartate have a 2-fold crystallographic symmetry axis and do not overlap, the observation of more than one class of binding sites must be due to a ligand-induced conformational change giving negative cooperativity. The closely related E. coli receptor was found to bind with only one class of sites but with a stoichiometry of one aspartate per dimer. The E. coli receptor thus binds with half-of-sites reactivity, an extreme form of negative cooperativity in which the second ligand is not observed to bind at all. Comparison of the X-ray crystal structure of the ligand binding domain with and without bound aspartate revealed ligand-induced conformational changes that explain the two examples of negative cooperativity.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Allosteric Regulation
  • Aspartic Acid / metabolism*
  • Crystallography, X-Ray
  • Escherichia coli / metabolism*
  • Kinetics
  • Ligands
  • Models, Molecular
  • Protein Conformation
  • Receptors, Amino Acid / metabolism*
  • Salmonella typhimurium / metabolism*

Substances

  • Ligands
  • Receptors, Amino Acid
  • aspartic acid receptor
  • Aspartic Acid