Probing protein packing surrounding the residues in and flanking the nicotinic acetylcholine receptor M2M3 loop.
Probing protein packing surrounding the residues in and flanking the nicotinic acetylcholine receptor M2M3 loop.
复制标题
DOI：
10.1523/jneurosci.4121-08.2009
复制
发表时间：
2009-02-11
期刊：
影响因子：
--
通讯作者：
Jansen M
中科院分区：
文献类型：
--
作者：
Wiltfong RE;Jansen M
Nicotinic Acetylcholine Receptors (nAChR) are cation-selective, ligand-gated ion channels of the Cys-loop gene superfamily. The recent crystal structure of a bacterial homologue from Erwinia chrysanthemi (ELIC) agrees with previous structures of the N-terminal domain of acetylcholine-binding protein (AChBP) and of the electronmicroscopy derived Torpedo nAChR structure. However, the ELIC transmembrane domain is significantly more tightly packed than the corresponding region of the Torpedo nAChR. We investigated the tightness of protein packing surrounding the extracellular end of the M2 transmembrane segment and around the loop connecting the M2 and M3 segments using the substituted cysteine accessibility method (SCAM). The M2 20′ to 27′ residues were highly water accessible and the variation in reaction rates were consistent with this region being α-helical. At all positions tested, the presence of ACh changed MTSEA modification rates by less than 10-fold. In the presence of ACh, reaction rates for residues in the last extracellular α-helical turn of M2 and in the M2M3 loop increased, whereas rates in M2's penultimate α-helical turn decreased. Only 3 out of 8 M2M3 loop residues were accessible to MTSEA in both the presence and absence of ACh. We infer that the protein packing around the M2M3 loop is tight, consistent with it's location at the interdomain interface where it is involved in the transduction of ligand binding in the extracellular domain to gating in the transmembrane domain. Our data indicate that the Torpedo nAChR transmembrane domain structure is a better model than the ELIC structure for eukaryotic Cys loop receptors.
