Caohuy H, Srivastava M, Pollard H B
Laboratory of Cell Biology and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Proc Natl Acad Sci U S A. 1996 Oct 1;93(20):10797-802. doi: 10.1073/pnas.93.20.10797.
Exocytotic membrane fusion and secretion are promoted by the concerted action of GTP and Ca2+, although the precise site(s) of action in the process are not presently known. However, the calcium-dependent membrane fusion reaction driven by synexin (annexin VII) is an in vitro model for this process, which we have now found to be further activated by GTP. The mechanism of fusion activation depends on the unique ability of synexin to bind and hydrolyze GTP in a calcium-dependent manner, both in vitro and in vivo in streptolysin O-permeabilized chromaffin cells. The required [Ca2+] for GTP binding by synexin is in the range of 50-200 microM, which is known to occur at exocytotic sites in chromaffin cells, neurons, and other cell types. Previous immunolocalization studies place synexin at exocytotic sites in chromaffin cells, and we conclude that synexin is an atypical G protein that may be responsible for both detecting and mediating the Ca2+/GTP signal for exocytotic membrane fusion.
胞吐性膜融合和分泌是由GTP和Ca2+的协同作用促进的，尽管目前该过程中确切的作用位点尚不清楚。然而，由联蛋白（膜联蛋白VII）驱动的钙依赖性膜融合反应是该过程的体外模型，我们现在发现它可被GTP进一步激活。融合激活机制取决于联蛋白在体外以及在链球菌溶血素O通透的嗜铬细胞体内以钙依赖性方式结合和水解GTP的独特能力。联蛋白结合GTP所需的[Ca2+]在50-200微摩尔范围内，已知这在嗜铬细胞、神经元和其他细胞类型的胞吐位点会出现。先前的免疫定位研究表明联蛋白存在于嗜铬细胞的胞吐位点，我们得出结论，联蛋白是一种非典型G蛋白，可能负责检测和介导胞吐性膜融合的Ca2+/GTP信号。
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