Uncoupling and turnover in a Cl-/H+ exchange transporter. Academic Article uri icon

Overview

abstract

  • The CLC-family protein CLC-ec1, a bacterial homologue of known structure, stoichiometrically exchanges two Cl(-) for one H(+) via an unknown membrane transport mechanism. This study examines mutations at a conserved tyrosine residue, Y445, that directly coordinates a Cl(-) ion located near the center of the membrane. Mutations at this position lead to "uncoupling," such that the H(+)/Cl(-) transport ratio decreases roughly with the volume of the substituted side chain. The uncoupled proteins are still able to pump protons uphill when driven by a Cl(-) gradient, but the extent and rate of this H(+) pumping is weaker in the more uncoupled variants. Uncoupling is accompanied by conductive Cl(-) transport that is not linked to counter-movement of H(+), i.e., a "leak." The unitary Cl(-) transport rate, measured in reconstituted liposomes by both a conventional initial-velocity method and a novel Poisson dilution approach, is approximately 4,000 s(-1) for wild-type protein, and the uncoupled mutants transport Cl(-) at similar rates.

publication date

  • April 1, 2007

Research

keywords

  • Antiporters
  • Chloride Channels
  • Escherichia coli Proteins

Identity

PubMed Central ID

  • PMC2151619

Scopus Document Identifier

  • 33947720910

Digital Object Identifier (DOI)

  • 10.1085/jgp.200709756

PubMed ID

  • 17389248

Additional Document Info

volume

  • 129

issue

  • 4