基于酵母产孢的syntaxin家族蛋白SNARE区域功能分析

Functional Analysis of the SNARE Domain of Syntaxin Family Proteins Using Yeast Sporulation

真核细胞中大部分膜融合过程由SNARE蛋白介导,但其功能和调节机制尚未完全清楚。酵母孢子形成是研究囊泡融合机制包括SNARE蛋白的理想模型系统。在该过程中涉及t-SNARE蛋白Sso1,它是突触囊泡融合所需蛋白syntaxin 1A的同源物,两者SNARE区域有51%的同源性。尽管如此,将SSO1的SNARE区域完全替换成syntaxin 1A,而构建的嵌合体却无法回补sso1△突变的产孢缺陷。为了确定哪些残基为Sso1功能所必须,作者进行了嵌合体和突变分析,发现Sso1/syntaxin 1A嵌合体中syntaxin 1A的SNARE区域的220位丙氨酸换成谷氨酸后获得产孢功能。另外,Sso1发生相应的突变-218位谷氨酸突变成丙氨酸后失去其功能。因此,218位谷氨酸残基为Sso1产孢功能所必须。

In eukaryotic cells, most of membrane fusion processes are mediated by SNARE proteins. However, its functional and regulatory mechanisms have not been fully understood. Previous study have shown that yeast sporulation was an ideal model system to manipulate and investigate vesicle fusion machinery including SNARE proteins. The t-SNARE protein Sso 1 involved in this process is an orthologue of syntaxin 1A which is required for the synaptic vesicle fusion,both share 51% homology at the SNRE domains. However, although their functional and amino acid sequence are similar,Ssol/syntaxin 1A chimera cannot complement the sporulation deficiency of ssolA mutant when SNARE domain of Ssol is replaced completely by syntaxin 1A. To determine which residues are critical for Ssol function,chimera and mutational analyses are further conducted. The results showed that the SSO1/syntaxin 1A chimera gain the functionality by replacing Ala220 residue to Glu in the syntaxin 1A SNARE domain. By contrast, Sso I lose its function by mutating the corresponding amino acid residue, Glu218 into Ala. Thus, Glu218 residue is specifically required for Ssol function.