An unconventional SNARE complex mediates exocytosis at the plasma membrane and vesicular fusion at the apical annuli in Toxoplasma gondii

Exocytosis is a key active process in cells by which proteins are released in bulk via the fusion of exocytic vesicles with the plasma membrane. Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein-mediated vesicle fusion with the plasma membrane is essential in most exocytotic pathways. In mammalian cells, the vesicular fusion step of exocytosis is normally mediated by Syntaxin-1 (Stx1) and SNAP25 family proteins (SNAP25 and SNAP23). However, in Toxoplasma gondii, a model organism of Apicomplexa, the only SNAP25 family protein, with a SNAP29-like molecular structure, is involved in vesicular fusion at the apicoplast. Here, we reveal that an unconventional SNARE complex comprising TgStx1, TgStx20, and TgStx21 mediates vesicular fusion at the plasma membrane. 

 

Comments：

Exocytosis is an active process by which cells release proteins and other molecules from the cell by fusing exocytic vesicles with the plasma membrane. This process is mediated by a group of proteins called SNAREs, which facilitate vesicle fusion with the plasma membrane. In mammalian cells, the SNARE proteins Syntaxin-1 and the SNAP25 family proteins are essential for vesicular fusion. However, in Toxoplasma gondii, a model organism of Apicomplexa, the SNAP25 family protein involved in vesicular fusion has a SNAP29-like molecular structure and is involved in vesicular fusion at the apicoplast.

In this study, it has been discovered that an unconventional SNARE complex comprising TgStx1, TgStx20, and TgStx21 mediates vesicular fusion at the plasma membrane in T. gondii. This SNARE complex is different from the conventional SNARE complex found in mammalian cells and indicates that T. gondii has evolved a unique mechanism for exocytosis. This discovery has important implications for understanding the biology of T. gondii and other Apicomplexa organisms and could lead to the development of new therapeutic targets for treating diseases caused by these parasites.

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