Voltage-dependent and -independent titration of specific residues accounts for complex gating of a ClC chloride channel by extracellular protons

Niemeyer, MI; Cid, LP; Yusef, YR; Briones, R; Sepulveda, FV

Abstract

The ClC transport protein family comprises both Cl- ion channel and H+/Cl- and H+/NO3 - exchanger members. Structural studies on a bacterial ClC transporter reveal a pore obstructed at its external opening by a glutamate side-chain which acts as a gate for Cl- passage and in addition serves as a staging post for H+ exchange. This same conserved glutamate acts as a gate to regulate Cl- flow in ClC channels. The activity of ClC-2, a genuine Cl- channel, has a biphasic response to extracellular pH with activation by moderate acidification followed by abrupt channel closure at pH values lower than ~7. We have now investigated the molecular basis of this complex gating behaviour. First, we identify a sensor that couples extracellular acidification to complete closure of the channel. This is extracellularly-facing histidine 532 at the N-terminus of transmembrane helix Q whose neutralisation leads to channel closure in a cooperative manner. We go on to show that acidification-dependent activation of ClC-2 is voltage dependent and probably mediated by protonation of pore gate glutamate 207. Intracellular Cl- acts as a voltage-independent modulator, as though regulating the pKa of the protonatable residue. Our results suggest that voltage dependence of ClC-2 is given by hyperpolarisation-dependent penetration of protons from the extracellular side to neutralise the glutamate gate deep within the channel, which allows Cl- efflux. This is reminiscent of a partial exchanger cycle, suggesting that the ClC-2 channel evolved from its transporter counterparts. © 2009 The Authors. Journal compilation © 2009 The Physiological Society.

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Título según WOS: Voltage-dependent and -independent titration of specific residues accounts for complex gating of a ClC chloride channel by extracellular protons
Título según SCOPUS: Voltage-dependent and -independent titration of specific residues accounts for complex gating of a ClC chloride channel by extracellular protons
Título de la Revista: JOURNAL OF PHYSIOLOGY-LONDON
Volumen: 587
Número: 7
Editorial: Wiley
Fecha de publicación: 2009
Página de inicio: 1387
Página final: 1400
Idioma: English
URL: http://www.jphysiol.org/cgi/doi/10.1113/jphysiol.2008.167353
DOI:

10.1113/jphysiol.2008.167353

Notas: ISI, SCOPUS