Berrera Marco, Pantano Sergio, Carloni Paolo
Scuola Internazionale Superiore di Studi Avanzati and Istituto Nazionale per la Fisica della Materia, Democritos Modeling Center for Research in Atomic Simulation, Trieste, Italy.
Biophys J. 2006 May 15;90(10):3428-33. doi: 10.1529/biophysj.105.071621. Epub 2006 Feb 24.
The hyperpolarization-activated cyclic nucleotide-modulated (HCN) cation channels are opened by membrane hyperpolarization, while their activation is modulated by the binding of cyclic adenosine monophosphate (cAMP) in the cytoplasm. Here we investigate the molecular basis of cAMP channel modulation by performing molecular dynamics simulations of a segment comprising the C-linker and the cyclic nucleotide binding domain (CNBD) in the presence and absence of cAMP, based on the available crystal structure of HCN2 from mouse. In presence of cAMP, the protein undergoes an oscillation of the quaternary structure on the order of 10 ns, not observed in the apoprotein. In contrast, the absence of ligand causes conformational rearrangements within the CNBDs, driving these domains to a more flexible state, similar to that described in CNBDs of other proteins. This increased flexibility causes a rather disordered movement of the CNBDs, resulting in an inhibitory effect on the channel. We propose that the cAMP-triggered large-scale oscillation plays an important role for the channel's function, being coupled to a motion of the C-linker which, in turn, modulates the gating of the channel.
超极化激活的环核苷酸调制（HCN）阳离子通道由膜超极化开启，而其激活则受细胞质中环磷酸腺苷（cAMP）结合的调节。在此，我们基于小鼠HCN2的现有晶体结构，通过对包含C-连接子和环核苷酸结合结构域（CNBD）的片段在有无cAMP情况下进行分子动力学模拟，来研究cAMP对通道调制的分子基础。在有cAMP存在时，蛋白质会发生约10纳秒量级的四级结构振荡，这在脱辅基蛋白中未观察到。相反，没有配体时会导致CNBDs内的构象重排，使这些结构域处于更灵活的状态，类似于其他蛋白质的CNBDs中所描述的那样。这种增加的灵活性导致CNBDs的运动相当无序，从而对通道产生抑制作用。我们提出，cAMP触发的大规模振荡对通道功能起着重要作用，它与C-连接子的运动相耦合，而C-连接子的运动又反过来调节通道的门控。
