Matulef K, Flynn G E, Zagotta W N
Molecular and Cellular Biology Program, University of Washington, Seattle 98105, USA.
Neuron. 1999 Oct;24(2):443-52. doi: 10.1016/s0896-6273(00)80857-0.
Cyclic nucleotide-gated (CNG) channels are activated in response to the direct binding of cyclic nucleotides to an intracellular domain. This domain is thought to contain a beta roll and two alpha helices, designated the B and C helices. To probe the conformational changes occurring in the ligand-binding domain during channel activation, we used the substituted cysteine accessibility method (SCAM). We found that a residue in the beta roll, C505, is more accessible in unliganded channels than in liganded channels, whereas a residue in the C helix, G597C, is more accessible in closed channels than in open channels. These results support a molecular mechanism for channel activation in which the ligand initially binds to the beta roll, followed by an opening allosteric transition involving the relative movement of the C helix toward the beta roll.
环核苷酸门控（CNG）通道是在环核苷酸直接结合到细胞内结构域时被激活的。该结构域被认为包含一个β折叠和两个α螺旋，分别称为B螺旋和C螺旋。为了探究通道激活过程中配体结合结构域发生的构象变化，我们使用了半胱氨酸替代可及性方法（SCAM）。我们发现，β折叠中的一个残基C505在未结合配体的通道中比在结合配体的通道中更易接近，而C螺旋中的一个残基G597C在关闭的通道中比在开放的通道中更易接近。这些结果支持了一种通道激活的分子机制，即配体最初结合到β折叠上，随后发生一种变构开放转变，涉及C螺旋向β折叠的相对移动。
