A picrotoxin-specific conformational change in the glycine receptor M2-M3 loop.

Hawthorne, Rebecca L. and Lynch, Joseph W. (2005) A picrotoxin-specific conformational change in the glycine receptor M2-M3 loop.. Journal of Biological Chemistry, 280 43: 35836-35843.


Author Hawthorne, Rebecca L.
Lynch, Joseph W.
Title A picrotoxin-specific conformational change in the glycine receptor M2-M3 loop.
Journal name Journal of Biological Chemistry   Check publisher's open access policy
ISSN 0021-9258
Publication date 2005
Sub-type Article (original research)
DOI 10.1074/jbc.M506645200
Volume 280
Issue 43
Start page 35836
End page 35843
Total pages 8
Editor Herbert Taylor
Place of publication Bethesda
Publisher Amer Soc Biochemistry Molecular Biology Inc
Collection year 2005
Language eng
Subject C1
270601 Animal Physiology - Biophysics
730104 Nervous system and disorders
Abstract The external loop linking the M2 and M3 transmembrane domains is crucial for coupling agonist binding to channel gating in the glycine receptor chloride channel (GlyR). A substituted cysteine accessibility scan previously showed that glycine activation increased the surface accessibility of 6 contiguous residues (Arg(271) Lys(276)) toward the N-terminal end of the homomeric alpha 1 GlyR M2 - M3 loop. In the present study we used a similar approach to determine whether the allosteric antagonist, picrotoxin, could impose conformational changes to this domain that cannot be induced by varying agonist concentrations alone. Picrotoxin slowed the reaction rate of a sulfhydryl-containing compound ( MTSET) with A272C, S273C, and L274C. Before interpreting this as a picrotoxin-specific conformational change, it was necessary to eliminate the possibility of steric competition between picrotoxin and MTSET. Accordingly, we showed that picrotoxin and the structurally unrelated blocker, bilobalide, were both trapped in the R271C GlyR in the closed state and that a point mutation to the pore-lining Thr(6') residue abolished inhibition by both compounds. We also demonstrated that the picrotoxin dissociation rate was linearly related to the channel open probability. These observations constitute a strong case for picrotoxin binding in the pore. We thus conclude that the picrotoxin-specific effects on the M2 - M3 loop are mediated allosterically. This suggests that the M2 - M3 loop responds differently to the occupation of different binding sites.
Keyword Biochemistry & Molecular Biology
Channel-lining Residues
Nicotinic Acetylcholine-receptor
Chloride Channels
Gaba(a) Receptor
Beta-subunit
Surface Accessibility
Alpha-subunit
M2 Segment
Pore
Identification
Biophysics
Q-Index Code C1

 
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