Premium
A Conserved Pore‐Lining Glutamate as a Voltage‐ and Chloride‐Dependent Gate in the ClC‐2 Chloride Channel
Author(s) -
Niemeyer María Isabel,
Cid L. Pablo,
Zúñiga Leandro,
Catalán Marcelo,
Sepúlveda Francisco V.
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2003.055988
Subject(s) - gating , extracellular , chloride channel , chemistry , biophysics , intracellular , protonation , chloride , patch clamp , stereochemistry , biochemistry , ion , biology , receptor , organic chemistry
ClC‐2 is a ubiquitously expressed, two‐pore homodimeric Cl − channel opened by hyperpolarisation. Little is known about its gating mechanisms. Crystallographic and functional studies in other ClC channels suggest that a conserved glutamate residue carboxylate side‐chain can close protopores by interacting with a Cl − ‐binding site in the pore. Competition for this site is thought to provide the molecular basis for gating by extracellular Cl − . We now show that ClC‐2 gating depends upon intra‐ but not extracellular Cl − and that neutralisation of E217, the homologous pore glutamate, leads to loss of sensitivity to intracellular Cl − and voltage. Experiments testing for transient activation by extracellular protons demonstrate that E217 is not available for protonation in the closed channel state but becomes so after opening by hyperpolarisation. The results suggest that E217 is a hyperpolarisation‐dependent protopore gate in ClC‐2 and that access of intracellular Cl − to a site normally occupied by its side‐chain in the pore stabilises the open state. A remaining hyperpolarisation‐dependent gate might correspond to that closing both pores simultaneously in other ClC channels.