Wang Jing, Shen Bing, Guo Min, Lou Xiaohua, Duan Yuanyuan, Cheng Xin Ping, Teng Maikun, Niu Liwen, Liu Qun, Huang Qingqiu, Hao Quan
Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China.
Biochemistry. 2005 Aug 2;44(30):10145-52. doi: 10.1021/bi050614m.
Cysteine-rich secretory proteins (CRISPs) are widespread in snake venoms. Some members of these CRISPs recently have been found to block L-type Ca(2+) channels or cyclic nucleotide-gated ion (CNG) channels. Here, natrin purified from Naja atra venom, a member of the CRISP family, can induce a further contractile response in the endothelium-denuded thoracic aorta of mouse which has been contracted by a high-K(+) solution. Further experiments show it can block the high-conductance calcium-activated potassium (BK(Ca)) channel in a concentration-dependent manner with an IC(50) of 34.4 nM and a Hill coefficient of 1.02, which suggests that only a single natrin molecule is required to bind an ion channel to block BK(Ca) current. The crystal structure of natrin displaying two domains in tandem shows its cysteine-rich domain (CRD) has relatively independent flexibility, especially for the C-terminal long loop (loop I) of CRD to participate in the interface of two domains. On the basis of previous studies of CNG channel and L-Ca(2+) channel blockers, and the sequence and structural comparison of natrin and stecrisp, the deviation of the vital loop I of CRD is suggested to contribute to different effects of some CRISPs in protein-protein interaction.
富含半胱氨酸的分泌蛋白（CRISPs）广泛存在于蛇毒中。最近发现这些CRISPs的一些成员能够阻断L型钙通道或环核苷酸门控离子（CNG）通道。在这里，从眼镜蛇毒中纯化得到的纳曲林（natrin），作为CRISP家族的一员，能够在已经被高钾溶液收缩的小鼠去内皮胸主动脉中诱导进一步的收缩反应。进一步的实验表明，它能够以浓度依赖的方式阻断高电导钙激活钾（BK（Ca））通道，IC50为34.4 nM，希尔系数为1.02，这表明仅需单个纳曲林分子结合离子通道即可阻断BK（Ca）电流。纳曲林的晶体结构显示其具有两个串联结构域，其富含半胱氨酸的结构域（CRD）具有相对独立的灵活性，特别是CRD的C末端长环（环I）参与两个结构域的界面。基于先前对CNG通道和L型钙通道阻滞剂的研究，以及纳曲林和stecrisp的序列和结构比较，提示CRD的关键环I的偏差导致一些CRISPs在蛋白质-蛋白质相互作用中具有不同的作用。
