Fairclough R H, Twaddle G M, Gudipati E, Lin M Y, Richman D P
Department of Neurology, University of California, Davis, CA 95616, USA.
J Mol Biol. 1998 Sep 18;282(2):317-30. doi: 10.1006/jmbi.1998.2001.
We have probed the surface accessibility of residues alpha187 to alpha199 of the Torpedo acetylcholine receptor with monoclonal antibody 383C, which binds uniquely to these residues. However, 383C binds to only one of the two alpha subunits in the membrane-bound receptor, neither of the two subunits in carbamylcholine-desensitized receptor, and to both alpha subunits in Triton X-100 solubilized receptor. The kinetics of association and dissoci-ation of 383C with the peptide alpha(183-199) compared to those with the membrane-bound receptor suggest that all but a single hydrogen bond of affinity derives from contacts between this peptide and the monoclonal antibody paratope. Inhibition of 383C binding by alpha-bungarotoxin selectively directed to the alpha subunit correlated with the high-affinity d-tubocurarine binding site, along with a lack of inhibition by alpha-bungarotoxin directed to the alpha subunit correlated with the low-affinity d-tubocurarine binding site, suggests that the 383C epitope on the membrane-bound receptor resides on the alpha subunit associated with the high-affinity d-tubocurarine binding site. The results presented here suggest a structural basis for the differences between the two receptor acetylcholine binding sites.
我们用单克隆抗体383C探究了电鳐乙酰胆碱受体α187至α199位残基的表面可及性，该抗体仅与这些残基结合。然而，383C仅与膜结合型受体中的两个α亚基之一结合，与氨甲酰胆碱脱敏受体中的两个亚基均不结合，而与Triton X-100溶解的受体中的两个α亚基都结合。与膜结合型受体相比，383C与肽α(183 - 199)结合和解离的动力学表明，除了一个氢键外，亲和力均来自该肽与单克隆抗体互补位之间的接触。选择性作用于α亚基的α-银环蛇毒素对383C结合的抑制作用与高亲和力的d-筒箭毒碱结合位点相关，而作用于α亚基的α-银环蛇毒素缺乏抑制作用与低亲和力的d-筒箭毒碱结合位点相关，这表明膜结合型受体上的383C表位位于与高亲和力d-筒箭毒碱结合位点相关的α亚基上。本文给出的结果提示了两种受体乙酰胆碱结合位点差异的结构基础。
