Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany.
Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
J Gen Physiol. 2018 Sep 3;150(9):1261-1271. doi: 10.1085/jgp.201711935. Epub 2018 Jun 29.
Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels are tetramers that elicit electrical rhythmicity in specialized brain neurons and cardiomyocytes. The channels are dually activated by voltage and binding of cyclic adenosine monophosphate (cAMP) to their four cyclic nucleotide-binding domains (CNBDs). Here we analyze the effects of cAMP binding to different concatemers of HCN2 channel subunits, each having a defined number of functional CNBDs. We show that each liganded CNBD promotes channel activation in an additive manner and that, in the special case of two functional CNBDs, functionality does not depend on the arrangement of the subunits. Correspondingly, the reverse process of deactivation is slowed by progressive liganding, but only if four and three ligands as well as two ligands in trans position (opposite to each other) are bound. In contrast, two ligands bound in cis positions (adjacent to each other) and a single bound ligand do not affect channel deactivation. These results support an activation mechanism in which each single liganded CNBD causes a turning momentum on the tetrameric ring-like structure formed by all four CNBDs and that at least two liganded subunits in trans positions are required to maintain activation.
超极化激活环核苷酸调节（HCN）通道是由四个亚基组成的四聚体，可在特定的脑神经元和心肌细胞中引发电节律。该通道通过电压和环磷酸腺苷（cAMP）与四个环核苷酸结合域（CNBD）的结合而双重激活。在这里，我们分析了 cAMP 与 HCN2 通道亚基的不同串联体结合的影响，每个串联体都具有定义数量的功能性 CNBD。我们表明，每个配体结合的 CNBD 以累加的方式促进通道激活，并且在两个功能性 CNBD 的特殊情况下，功能不依赖于亚基的排列。相应地，渐进配体的反向失活过程会减慢，但只有当四个和三个配体以及两个处于反式位置（彼此相对）的配体结合时才会发生这种情况。相比之下，两个处于顺式位置（彼此相邻）的配体和一个结合的配体不会影响通道失活。这些结果支持一种激活机制，其中每个单独配体结合的 CNBD 都会在由四个 CNBD 形成的环状四聚体结构上产生转动动量，并且至少需要两个处于反式位置的配体结合亚基来维持激活。
