Molecular mechanism of cAMP modulation of HCN pacemaker channels
Molecular mechanism of cAMP modulation of HCN pacemaker channels
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DOI：
10.1038/35081088
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发表时间：
2001-06-14
期刊：
影响因子：
64.8
通讯作者：
Tibbs, GR
中科院分区：
文献类型：
--
作者：
Wainger, BJ;DeGennaro, M;Tibbs, GR
HCN基因家族的超极化激活阳离子通道（1-6）有助于心脏（7）和大脑（5，6，8）的自发节律活动。所有四个家族成员都含有与电压门控K+通道的S1-S6区域同源的核心跨膜段结构域和羧基末端120个氨基酸的环核苷酸结合结构域（CNBD）基序。Homocyte CNBD负责直接激活环核苷酸门控通道和调节HERG电压门控K+通道-分别对视觉和嗅觉信号传导（9）和心脏复极化（10）很重要。环AMP与HCN通道胞质位点的直接结合允许通道在动作电位复极化后更快速和完全地打开（1，2，11），从而加速节律发生（6-8）。然而，cAMP结合调节HCN通道门控的机制和HCN亚型之间功能差异的基础仍然未知。在这里，我们通过构建截短突变体证明CNBD抑制核心跨膜结构域的激活。cAMP结合解除这种抑制。HCN 1和HCN 2亚型之间的激活门控和cAMP调节程度的差异主要来自CNBD抑制功效的差异。
Hyperpolarization-activated cation channels of the HCN gene family(1-6) contribute to spontaneous rhythmic activity in both heart(7) and brain(5,6,8). All four family members contain both a core transmembrane segment domain, homologous to the S1-S6 regions of voltage-gated K+ channels, and a carboxy-terminal 120 amino-acid cyclic nucleotide-binding domain (CNBD) motif. Homologous CNBDs are responsible for the direct activation of cyclic nucleotide-gated channels and for modulation of the HERG voltage-gated K+ channel-important for visual and olfactory signalling(9) and for cardiac repolarization(10), respectively. The direct binding of cyclic AMP to the cytoplasmic site on HCN channels permits the channels to open more rapidly and completely after repolarization of the action potential(1,2,11), thereby accelerating rhythmogenesis(6-8). However, the mechanism by which cAMP binding modulates HCN channel gating and the basis for functional differences between HCN isoforms remain unknown. Here we demonstrate by constructing truncation mutants that the CNBD inhibits activation of the core transmembrane domain. cAMP binding relieves this inhibition. Differences in activation gating and extent of cAMP modulation between the HCN1 and HCN2 isoforms result largely from differences in the efficacy of CNBD inhibition.