Volume 271, Number 27,
Issue of July 5, 1996
pp. 16035-16039
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.
An Amino Acid Substitution in the Pore Region of a
Glutamate-gated Chloride Channel Enables the Coupling of Ligand
Binding to Channel Gating
(Received for publication, January 26, 1996, and in revised form, April 16, 1996)
Adrian
Etter
,
Doris F.
Cully
,
James M.
Schaeffer
,
Ken K.
Liu
and
Joseph P.
Arena
From the Merck Research Laboratories, Department of Cell
Biochemistry and Physiology,
Department of Genetics
and Molecular Biology, Rahway, New Jersey 07065-0900
Many of the subunits of ligand-gated ion channels
respond poorly, if at all, when expressed as homomeric channels in
Xenopus oocytes. This lack of a ligand response has been
thought to result from poor surface expression, poor assembly, or lack
of an agonist binding domain. The Caenorhabditis elegans
glutamate-gated chloride channel subunit GluCl
responds to glutamate
as a homomeric channel while the GluCl
subunit is insensitive. A
chimera between GluCl
and GluCl
was used to suggest that major
determinants for glutamate binding are present on the GluCl
N
terminus. Amino acid substitutions in the presumed pore of GluCl
conferred direct glutamate gating indicating that GluCl
is deficient
in coupling of ligand binding to channel gating. Heteromeric channels
of GluCl
+
may differ from the prototypic muscle nicotinic
acetylcholine receptor in that they have the potential to bind ligand
to all of the subunits forming the channel.