Structural Biology Center, National Institute of Genetics/SOKENDAI, Mishima-Shizuoka, Japan.
PLoS Pathog. 2009 Nov;5(11):e1000670. doi: 10.1371/journal.ppat.1000670. Epub 2009 Nov 26.
Group A streptococcus (GAS; Streptococcus pyogenes) is a common pathogen that invades non-phagocytic human cells via endocytosis. Once taken up by cells, it escapes from the endocytic pathway to the cytoplasm, but here it is contained within a membrane-bound structure termed GAS-containing autophagosome-like vacuoles (GcAVs). The autophagosome marker GFP-LC3 associates with GcAVs, and other components of the autophagosomal pathway are involved in GcAV formation. However, the mechanistic relationship between GcAV and canonical autophagy is largely unknown. Here, we morphologically analyzed GcAV formation in detail. Initially, a small, GFP-LC3-positive GcAV sequesters each streptococcal chain, and these then coalesce into a single, large GcAV. Expression of a dominant-negative form of Rab7 or RNAi-mediated knockdown of Rab7 prevented the initial formation of small GcAV structures. Our results demonstrate that mechanisms of GcAV formation includes not only the common machinery of autophagy, but also Rab7 as an additional component, which is dispensable in canonical autophagosome formation.
A 组链球菌（GAS；化脓性链球菌）是一种常见的病原体，通过内吞作用侵入非吞噬性的人类细胞。一旦被细胞摄取，它就会从吞噬途径逃到细胞质中，但此时它被包含在一种称为含 GAS 的自噬体样空泡（GcAV）的膜结合结构中。自噬体标记 GFP-LC3 与 GcAV 相关联，并且自噬体途径的其他成分参与 GcAV 的形成。然而，GcAV 和经典自噬之间的机制关系在很大程度上尚不清楚。在这里，我们详细地对 GcAV 的形成进行了形态学分析。最初，一个小的 GFP-LC3 阳性的 GcAV 隔离每个链球菌链，然后这些链球菌链合并成一个单一的大 GcAV。Rab7 的显性负形式的表达或 Rab7 的 RNAi 介导的敲低阻止了小 GcAV 结构的初始形成。我们的结果表明，GcAV 形成的机制不仅包括自噬的常见机制，还包括 Rab7 作为一个额外的组成部分，它在经典自噬体形成中是可有可无的。
