Acetylcholine receptor gating at extracellular transmembrane domain interface: the Cys-loop and M2-M3 linker

作者：Jha Archana; Cadugan David J; Purohit Prasad; Auerbach Anthony^*

来源：Journal of General Physiology, 2007, 130(6): 547-558.

DOI：10.1085/jgp.200709856

Acetylcholine receptor channel gating is a propagated conformational cascade that links changes in structure and function at the transmitter binding sites in the extracellular domain (ECD) with those at a "gate" in the transmembrane domain (TMD). We used Phi-value analysis to probe the relative timing of the gating motions of alpha-subunit residues located near the ECD-TMD interface. Mutation of four of the seven amino acids in the M2-M3 linker (which connects the pore-lining M2 helix with the M3 helix), including three of the four residues in the core of the linker, changed the diliganded gating equilibrium constant (K-eq) by up to 10,000-fold (P272 > 1274 > A270 > G275). The average Phi-value for the whole linker was similar to 0.64. One interpretation of this result is that the gating motions of the M2-M3 linker are approximately synchronous with those of much of M2 (similar to 0.64), but occur after those of the transmitter binding site region (similar to 0.93) and loops 2 and 7 (similar to 0.77). We also examined mutants of six cys-loop residues (VI 32, TI 33, HI 34, F1 35, P1 36, and F1 37). Mutation of VI 32, HI 34, and F1 35 changed K-eq by 2800-, 10-, and 18-fold, respectively, and with an average Phi-value of 0.74, similar to those of other cys-loop residues. Even though V132 and 1274 are close, the energetic coupling between I and V mutants of these positions was small (<= 0.51 kcal mol(-1)). The M2-M3 linker appears to be the key moving part that couples gating motions at the base of the ECD with those in TMD. These interactions are distributed along an similar to 16-angstrom border and involve about a dozen residues.

• 出版日期2007-12