Uncoupling and turnover in a Cl-/H+ exchange transporter.

TitleUncoupling and turnover in a Cl-/H+ exchange transporter.
Publication TypeJournal Article
Year of Publication2007
AuthorsWalden M, Accardi A, Wu F, Xu C, Williams C, Miller C
JournalJ Gen Physiol
Date Published2007 Apr
KeywordsAmino Acid Substitution, Antiporters, Chloride Channels, Chlorides, Dimerization, Escherichia coli, Escherichia coli Proteins, Liposomes, Models, Chemical, Molecular Sequence Data, Mutation, Poisson Distribution, Protein Structure, Tertiary, Protons

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.

Alternate JournalJ. Gen. Physiol.
PubMed ID17389248
PubMed Central IDPMC2151619
Grant ListR01-31768 / / PHS HHS / United States