Department of Anesthesiology, Pharmacology and Therapeutics, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada, V6T 1Z3.
Proc Natl Acad Sci U S A. 2012 Feb 28;109(9):3558-63. doi: 10.1073/pnas.1114748109. Epub 2012 Feb 13.
Voltage-gated sodium channels underlie the rapid regenerative upstroke of action potentials and are modulated by cytoplasmic calcium ions through a poorly understood mechanism. We describe the 1.35 Å crystal structure of Ca(2+)-bound calmodulin (Ca(2+)/CaM) in complex with the inactivation gate (DIII-IV linker) of the cardiac sodium channel (Na(V)1.5). The complex harbors the positions of five disease mutations involved with long Q-T type 3 and Brugada syndromes. In conjunction with isothermal titration calorimetry, we identify unique inactivation-gate mutations that enhance or diminish Ca(2+)/CaM binding, which, in turn, sensitize or abolish Ca(2+) regulation of full-length channels in electrophysiological experiments. Additional biochemical experiments support a model whereby a single Ca(2+)/CaM bridges the C-terminal IQ motif to the DIII-IV linker via individual N and C lobes, respectively. The data suggest that Ca(2+)/CaM destabilizes binding of the inactivation gate to its receptor, thus biasing inactivation toward more depolarized potentials.
电压门控钠离子通道是动作电位快速再生上升的基础，其活性通过一种尚未完全阐明的机制受到细胞质钙离子的调节。我们描述了钙结合钙调蛋白（Ca2+/CaM）与心脏钠离子通道（NaV1.5）失活门（DIII-IV 连接子）复合物的 1.35Å 晶体结构。该复合物包含五个与长 QT 型 3 型和 Brugada 综合征相关疾病突变的位置。结合等温滴定量热法，我们确定了独特的失活门突变，这些突变增强或减弱了 Ca2+/CaM 的结合，进而在电生理实验中使全长通道对 Ca2+的调节变得敏感或消除。其他生化实验支持这样一种模型，即单个 Ca2+/CaM 通过各自的 N 和 C 结构域分别将 C 端 IQ 基序与 DIII-IV 连接子桥接。这些数据表明，Ca2+/CaM 会破坏失活门与其受体的结合，从而使失活门更偏向于去极化电位。
