MUNC18-1 (also known as STXBP1) is an essential protein for docking and fusion of secretory vesicles. Mouse chromaffin cells (MCCs) lacking MUNC18-1 show impaired secretory vesicle docking, but also mistargeting of SNARE protein syntaxin1 and an abnormally dense submembrane F-actin network. Here, we tested the contribution of both these phenomena to docking and secretion defects in MUNC18-1-deficient MCCs. We show that an abnormal F-actin network and syntaxin1 targeting defects are not observed in Snap25- or Syt1-knockout (KO) MCCs, which are also secretion deficient. We identified a MUNC18-1 mutant (V263T in β-sheet 10) that fully restores syntaxin1 targeting but not F-actin abnormalities in Munc18-1-KO cells. MUNC18-2 and -3 (also known as STXBP2 and STXBP3, respectively), which lack the hydrophobic residue at position 263, also did not restore a normal F-actin network in Munc18-1-KO cells. However, these proteins did restore the normal F-actin network when a hydrophobic residue was introduced at the corresponding position. Munc18-1-KO MCCs expressing MUNC18-1(V263T) showed normal vesicle docking and exocytosis. These results demonstrate that MUNC18-1 regulates the F-actin network independently of syntaxin1 targeting via hydrophobicity in β-sheet 10. The abnormally dense F-actin network in Munc18-1-deficient cells is not a rate-limiting barrier in secretory vesicle docking or fusion.This article has an associated First Person interview with the first author of the paper.

中文翻译：

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MUNC18-1通过β-sheet10中的疏水性独立于语法1靶向调节亚膜F-肌动蛋白网络。

MUNC18-1（也称为STXBP1）是分泌性小泡对接和融合的必需蛋白。缺少MUNC18-1的小鼠嗜铬细胞（MCC）显示出受损的囊泡对接受损，但SNARE蛋白syntaxin1的靶向错误以及异常密集的亚膜F-肌动蛋白网络。在这里，我们测试了这两种现象对MUNC18-1缺陷MCC中对接和分泌缺陷的贡献。我们表明，在Snap25-或Syt1-基因敲除（KO）MCC中也未观察到异常的F-肌动蛋白网络和syntaxin1靶向缺陷，这也是分泌不足的。我们确定了一个MUNC18-1突变体（β-sheet10中的V263T），该突变体可以完全恢复Munc18-1-KO细胞中syntaxin1的靶向性，但不能完全恢复F-肌动蛋白的异常。MUNC18-2和-3（分别也称为STXBP2和STXBP3），在263位缺少疏水残基，也没有在Munc18-1-KO细胞中恢复正常的F-肌动蛋白网络。但是，当在相应位置引入疏水残基时，这些蛋白质确实恢复了正常的F-肌动蛋白网络。表达MUNC18-1（V263T）的Munc18-1-KO MCC显示正常的囊泡对接和胞吐作用。这些结果表明，MUNC18-1独立于F-肌动蛋白网络通过β-sheet10中的疏水性来调节句法定位。在Munc18-1缺陷细胞中异常密集的F-肌动蛋白网络不是分泌性小泡对接的限速屏障。或融合。本文与本文的第一作者进行了第一人称访谈。表达MUNC18-1（V263T）的Munc18-1-KO MCC显示正常的囊泡对接和胞吐作用。这些结果表明，MUNC18-1独立于F-肌动蛋白网络通过β-sheet10中的疏水性来调节句法定位。在Munc18-1缺陷细胞中异常密集的F-肌动蛋白网络不是分泌性小泡对接的限速屏障。或融合。本文与本文的第一作者进行了第一人称访谈。表达MUNC18-1（V263T）的Munc18-1-KO MCC显示正常的囊泡对接和胞吐作用。这些结果表明，MUNC18-1独立于F-肌动蛋白网络通过β-sheet10中的疏水性来调控语法素1的靶向。Munc18-1缺陷细胞中异常密集的F-肌动蛋白网络不是分泌性囊泡对接的限速屏障。或融合。本文与本文的第一作者进行了第一人称访谈。