The soluble -ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex forms a 4-helix coiled-coil bundle consisting of 16 layers of interacting side chains upon membrane fusion. The central layer (layer 0) is highly conserved and comprises three glutamines (Q) and one arginine (R), and thus SNAREs are classified into Qa-, Qb-, Qc-, and R-SNAREs. Homotypic vacuolar fusion in requires the SNAREs Vam3 (Qa), Vti1 (Qb), Vam7 (Qc), and Nyv1 (R). However, the yeast strain lacking () shows no vacuole fragmentation, whereas the and strains display fragmented vacuoles. Here, we provide genetic evidence that the R-SNAREs Ykt6 and Nyv1 are functionally redundant in vacuole homotypic fusion using a newly isolated mutant. We observed the mutant showed no defect in vacuole morphology, but the double mutant had highly fragmented vacuoles. Furthermore, we show the defect in homotypic vacuole fusion caused by the mutation was compensated by the or mutations, which maintained the 3Q:1R ratio in the layer 0 of the SNARE complex, indicating that Nyv1 is exchangeable with Ykt6 in the vacuole SNARE complex. Unexpectedly, we found Ykt6 assembled with exocytic Q-SNAREs when the intrinsic exocytic R-SNAREs Snc1 and its paralog Snc2 lose their ability to assemble into the exocytic SNARE complex. These results suggest that Ykt6 may serve as a backup when other R-SNAREs become dysfunctional and that this flexible assembly of SNARE complexes may help cells maintain the robustness of the vesicular transport network.

中文翻译：

---

Ykt6 与酿酒酵母中的液泡和胞吐 R-SNARE 功能重叠


可溶性乙基马来酰亚胺敏感因子附着蛋白受体 (SNARE) 复合物在膜融合后形成 4 螺旋卷曲螺旋束，由 16 层相互作用的侧链组成。中心层（第0层）高度保守，包含3个谷氨酰胺（Q）和1个精氨酸（R），因此SNARE分为Qa-、Qb-、Qc-和R-SNARE。同型空泡融合需要 SNARE Vam3 (Qa)、Vti1 (Qb)、Vam7 (Qc) 和 Nyv1 (R)。然而，缺少 () 的酵母菌株未显示液泡破碎，而 和 菌株则显示破碎的液泡。在这里，我们提供了遗传证据，表明 R-SNARE Ykt6 和 Nyv1 在使用新分离的突变体的液泡同型融合中具有功能冗余。我们观察到突变体的液泡形态没有缺陷，但双突变体的液泡高度破碎。此外，我们发现突变引起的同型液泡融合缺陷被 或 突变补偿，保持了 SNARE 复合体第 0 层的 3Q:1R 比例，表明 Nyv1 与液泡 SNARE 复合体中的 Ykt6 是可互换的。出乎意料的是，当内在的胞吐 R-SNARE Snc1 及其旁系同源物 Snc2 失去组装成胞吐 SNARE 复合体的能力时，我们发现 Ykt6 与胞吐 Q-SNARE 组装在一起。这些结果表明，当其他 R-SNARE 功能失调时，Ykt6 可以作为备份，并且 SNARE 复合物的这种灵活组装可以帮助细胞维持囊泡运输网络的稳健性。