Key Laboratory of Birth Defects and Related Diseases of Women and Children, Department of Paediatrics, West China Second University Hospital, State Key Laboratory of Biotherapy and Collaborative Innovation Center of Biotherapy, Sichuan University, 610041 Chengdu, China.
Department of Pediatric Surgery and Laboratory of Stem Cell Biology, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, 610041 Chengdu, China.
Proc Natl Acad Sci U S A. 2020 Mar 24;117(12):6559-6570. doi: 10.1073/pnas.1919698117. Epub 2020 Mar 10.
Secretagogin (SCGN) is a hexa-EF-hand protein that is highly expressed in the pancreas, brain, and gastrointestinal tract. SCGN is known to modulate regulated exocytosis in multiple cell lines and tissues; however, its exact functions and underlying mechanisms remain unclear. Here, we report that SCGN interacts with the plasma membrane SNARE SNAP-25, but not the assembled SNARE complex, in a Ca-dependent manner. The crystal structure of SCGN in complex with a SNAP-25 fragment reveals that SNAP-25 adopts a helical structure and binds to EF-hands 5 and 6 of SCGN. SCGN strongly inhibits SNARE-mediated vesicle fusion in vitro by binding to SNAP-25. SCGN promotes the plasma membrane localization of SNAP-25, but not Syntaxin-1a, in SCGN-expressing cells. Finally, SCGN controls neuronal growth and brain development in zebrafish, likely via interacting with SNAP-25 or its close homolog, SNAP-23. Our results thus provide insights into the regulation of SNAREs and suggest that aberrant synapse functions underlie multiple neurological disorders caused by SCGN deficiency.
分泌蛋白 SECRETOGIN（SCGN）是一种六 EF 手蛋白，在胰腺、大脑和胃肠道中高度表达。已知 SCGN 可调节多种细胞系和组织中的调节性胞吐作用；然而，其确切功能和潜在机制仍不清楚。在这里，我们报告 SCGN 以 Ca2+依赖性方式与质膜 SNARE SNAP-25 相互作用，但不与组装的 SNARE 复合物相互作用。SCGN 与 SNAP-25 片段的晶体结构表明，SNAP-25 呈螺旋结构，并与 SCGN 的 EF 手 5 和 6 结合。SCGN 通过与 SNAP-25 结合强烈抑制体外 SNARE 介导的囊泡融合。SCGN 促进表达 SCGN 的细胞中 SNAP-25 的质膜定位，而不是 Syntaxin-1a。最后，SCGN 在斑马鱼中控制神经元生长和大脑发育，可能通过与 SNAP-25 或其密切同源物 SNAP-23 相互作用。因此，我们的结果提供了对 SNARE 调节的深入了解，并表明由 SCGN 缺乏引起的多种神经紊乱是由于突触功能异常所致。
