β subunit m2–m3 loop conformational changes are uncoupled from α1 β glycine receptor channel gating implications for human hereditary hyperekplexiaβ亚基m2-m3循环构象变化分道扬镳α1β甘氨酸受体对人类遗传hyperekplexia通道控制的影响.pdfVIP

b Subunit M2–M3 Loop Conformational Changes Are Uncoupled from a 1 b Glycine Receptor Channel Gating: Implications for Human Hereditary Hyperekplexia 1 1 1,2 Qiang Shan *, Lu Han , Joseph W. Lynch 1 Queensland Brain Institute, University of Queensland, Brisbane, Queensland, Australia, 2 School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia Abstract Hereditary hyperekplexia, or startle disease, is a neuromotor disorder caused mainly by mutations that either prevent the surface expression of, or modify the function of, the human heteromeric a 1 b glycine receptor (GlyR) chloride channel. There is as yet no explanation as to why hyperekplexia mutations that modify channel function are almost exclusively located in the a1 to the exclusion of b subunit. The majority of these mutations are identified in the M2–M3 loop of the a1 subunit. Here we demonstrate that a1 b GlyR channel function is less sensitive to hyperekplexia-mimicking mutations introduced into the M2–M3 loop of the b than into the a1 subunit. This suggests that the M2–M3 loop of the a subunit dominates the b subunit in gating the a 1 b GlyR channel. A further attempt to determine the possible mechanism underlying this phenomenon by using the voltage-clamp fluorometry technique revealed that agonist-induced conformational changes in the b subunit M2–M3 loop were uncoupled from a1 b GlyR channel gating. This is in contrast to the a subunit, where the M2–M3 loop conformational changes were shown to be directly coupled to a1 b GlyR channel gating. Finally, based on analysis of a 1 b chimeric receptors, we demonstrate that the structural components responsible for this are distributed throughout the b subunit, implying that the b subunit has evolved without the functional constrain