Brandhorst Dorothea, Zwilling Daniel, Rizzoli Silvio O, Lippert Undine, Lang Thorsten, Jahn Reinhard
Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
Proc Natl Acad Sci U S A. 2006 Feb 21;103(8):2701-6. doi: 10.1073/pnas.0511138103. Epub 2006 Feb 9.
Membrane fusion in the secretory pathway is mediated by soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins. Different fusion steps are thought to be effected by independent sets of SNAREs, but it is unclear whether specificity is determined by an intrinsic specificity of SNARE pairing or by upstream factors. Using a newly developed microscopy-based assay, we have investigated the SNARE specificity of homotypic early endosomal fusion. We show that early endosomes contain multiple sets of SNAREs, including, in addition to the putative early endosomal SNAREs, those involved in exocytosis and in fusion of late endosomes. We demonstrate that fusion is largely mediated by a complex formed by syntaxin 13, syntaxin 6, vti1a, and VAMP4, whereas the exocytic and late endosomal SNAREs play little or no role in the reaction. In contrast, proteoliposomes reconstituted with early endosomal SNAREs promiscuously fuse with liposomes containing exocytotic or late endosomal SNAREs. We conclude that the specificity of SNARE pairing does not suffice to determine the specificity of organelle fusion.
分泌途径中的膜融合由可溶性N - 乙基马来酰亚胺敏感因子附着受体（SNARE）蛋白介导。不同的融合步骤被认为由独立的SNARE蛋白组介导，但尚不清楚特异性是由SNARE配对的内在特异性还是由上游因子决定。使用新开发的基于显微镜的检测方法，我们研究了同型早期内体融合的SNARE特异性。我们发现早期内体含有多组SNARE蛋白，除了假定的早期内体SNARE蛋白外，还包括那些参与胞吐作用和晚期内体融合的蛋白。我们证明融合主要由 syntaxin-13、syntaxin-6、vti1a和VAMP4形成的复合物介导，而胞吐和晚期内体SNARE蛋白在该反应中作用很小或不起作用。相反，用早期内体SNARE蛋白重建的蛋白脂质体与含有胞吐或晚期内体SNARE蛋白的脂质体随意融合。我们得出结论，SNARE配对的特异性不足以决定细胞器融合的特异性。
