期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 286, 期 6, 页码 4420-4428出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M110.188730
关键词
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资金
- National Institutes of Health, NIEHS
- FWO-Vlaanderen [G.0330.06, G.0257.08]
- Belgian Federal Science Policy Office [P6/31]
- EU [2020288]
- KULeuven Onderzoekstoelage [OT/08/048]
Covalent modification of alpha 7 W55C nicotinic acetylcholine receptors (nAChR) with the cysteine-modifying reagent [2-(trimethylammonium) ethyl] methanethiosulfonate (MTSET+) produces receptors that are unresponsive to acetylcholine, whereas methyl methanethiolsulfonate (MMTS) produces enhanced acetylcholine-gated currents. Here, we investigate structural changes that underlie the opposite effects of MTSET+ and MMTS using acetylcholine-binding protein (AChBP), a homolog of the extracellular domain of the nAChR. Crystal structures of Y53C AChBP show that MT-SET+-modification stabilizes loop C in an extended conformation that resembles the antagonist-bound state, which parallels our observation that MTSET+ produces unresponsive W55C nAChRs. The MMTS-modified mutant in complex with acetylcholine is characterized by a contracted C-loop, similar to other agonist-bound complexes. Surprisingly, we find two acetylcholine molecules bound in the ligand-binding site, which might explain the potentiating effect of MMTS modification in W55C nAChRs. Unexpectedly, we observed in the MMTS-Y53C structure that ten phosphate ions arranged in two rings at adjacent sites are bound in the vestibule of AChBP. We mutated homologous residues in the vestibule of alpha 1 GlyR and observed a reduction in the single channel conductance, suggesting a role of this site in ion permeation. Taken together, our results demonstrate that targeted modification of a conserved aromatic residue in loop D is sufficient for a conformational switch of AChBP and that a defined region in the vestibule of the extracellular domain contributes to ion conduction in an-ion-selective Cys-loop receptors.
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