Xu Pingyong, Lu Jingze, Li Zhengzheng, Yu Xiaoqing, Chen Liangyi, Xu Tao
National Key Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Science, Beijing 100101, PR China.
Biochem Biophys Res Commun. 2006 Dec 1;350(4):969-76. doi: 10.1016/j.bbrc.2006.09.134. Epub 2006 Oct 4.
STIM1 and Orai1 have recently been identified to be crucial in the regulation of store-operated Ca(2+) entry. However, it remains to be established how STIM1 couples store depletion to the functioning of Orai1 in the plasma membrane. Using quantitative measurement, we find little STIM1 on the surface membrane which is not increased by store depletion. We further demonstrate that Orai1 assembles into clusters that co-localize with STIM1 aggregations upon store depletion. The clustering of Orai1 is only seen when Oari1 are co-expressed with STIM1, but not when expressed alone. Moreover, ER retreat from cell periphery leads to mismatching of Orai1 and STIM1 puncta. Therefore, we propose that store depletion causes aggregation and translocation of STIM1 in close apposition to the plasma membrane, which in turn recruits Orai1 in the plasma membrane to the sites of STIM1 aggregates to assemble functional units of CRAC channels in a stoichiometric manner.
近期研究发现，基质相互作用分子1（STIM1）和钙释放激活钙通道蛋白1（Orai1）在调控钙库操纵性钙内流过程中发挥关键作用。然而，STIM1如何将内质网钙库排空与质膜上Orai1的功能联系起来，仍有待进一步研究。通过定量测量，我们发现质膜上的STIM1含量极少，且内质网钙库排空不会使其增加。我们进一步证明，内质网钙库排空后，Orai1会聚集形成簇，并与STIM1的聚集物共定位。只有当Orai1与STIM1共表达时，才会出现Orai1的聚集现象，单独表达时则不会。此外，内质网从细胞周边区域退缩会导致Orai1和STIM1斑点的错配。因此，我们提出，内质网钙库排空会导致STIM1聚集并转移至紧邻质膜的位置，进而将质膜上的Orai1招募至STIM1聚集部位，以化学计量方式组装成钙释放激活钙通道（CRAC）的功能单位。
