Law Richard J, Lightstone Felice C
Biosciences and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, USA.
Biophys J. 2009 Sep 16;97(6):1586-94. doi: 10.1016/j.bpj.2009.06.044.
Protein motions in the Cys-loop ligand-gated ion receptors that govern the gating mechanism are still not well understood. The details as to how motions in the ligand-binding domain are translated to the transmembrane domain and how subunit rotations are linked to bring about the cooperative movements involved in gating are under investigation. Homology models of the alpha4beta2 nicotinic acetylcholine (nACh) and beta2alpha1gamma2 GABA receptors were constructed based on the torpedo neuromuscular-like nicotinic receptor structure. The template constructed for the full electron microscopy structure must be considered more reliable for structure-function studies due to the preservation of the E45-R209 salt-link. Many other salt-links are seen to transiently form, including switching off of the E45-R209 link, within a network of potential salt-links at the binding domain to the transmembrane domain interface region. Several potentially important intersubunit salt-links form in both the nAChR and GABAR structures during the simulation and appear conserved across many subunit combinations, such as the salt-link between alpha4.E262 and beta2.K255 in nAChR (beta2.E262 and alpha1.K263 in GABAR), at the top of the pore-lining M2 helices, and the intersubunit link of R210 on the M1-linker to E168 on the beta8-sheet of the adjacent subunit in the GABA receptor (E175-K46 being the structurally equivalent link in the nAChR, with reversed polarity). A network of other salt-links may be vital for transmitting the cooperative gating motions between subunits that become biased upon ligand binding. The changes seen in the simulations suggest that this network of salt-links helps to set limits and specific states for the conformational changes involved in gating of the receptor. We hope that these hypotheses will be tested experimentally in the near future.
半胱氨酸环配体门控离子受体中控制门控机制的蛋白质运动仍未得到很好的理解。关于配体结合结构域中的运动如何转化为跨膜结构域，以及亚基旋转如何联系起来以引发门控中涉及的协同运动的细节正在研究中。基于电鳐神经肌肉样烟碱受体结构构建了α4β2烟碱型乙酰胆碱（nACh）和β2α1γ2GABA受体的同源模型。由于E45-R209盐桥得以保留，为完整电子显微镜结构构建的模板对于结构-功能研究而言必定更可靠。在结合结构域与跨膜结构域界面区域的潜在盐桥网络中，可以看到许多其他盐桥会短暂形成，包括E45-R209盐桥的断开。在模拟过程中，nAChR和GABAR结构中均形成了几个潜在重要的亚基间盐桥，并且在许多亚基组合中似乎是保守的，例如nAChR中α4.E262和β2.K255之间的盐桥（GABAR中为β2.E262和α1.K263），位于孔内衬M2螺旋的顶部，以及GABA受体中M1连接子上的R210与相邻亚基β8折叠上的E168之间的亚基间连接（E175-K46是nAChR中结构等效的连接，但极性相反）。其他盐桥网络对于在配体结合时偏向的亚基之间传递协同门控运动可能至关重要。模拟中看到的变化表明，这个盐桥网络有助于为受体门控所涉及的构象变化设定限制和特定状态。我们希望这些假设能在不久的将来得到实验验证。
