Sequential interactions with Sec23 control the direction of vesicle traffic.

Area of Science:

• Cell Biology
• Molecular Biology
• Membrane Trafficking

Background:

• Directionality of vesicle traffic is crucial for cellular function.
• The Sec23p/Sec24p coat complex mediates vesicle budding from the endoplasmic reticulum (ER).
• The precise mechanisms of coat release and its relation to membrane fusion remain unclear.

Purpose of the Study:

• To investigate the role of the Sec23p/Sec24p coat complex in ER-Golgi vesicle traffic directionality.
• To identify factors and mechanisms regulating coat release and vesicle fusion.
• To understand how unidirectional transport is maintained and back-fusion is prevented.

Main Methods:

• Utilized a yeast transport assay to track ER-derived vesicles.
• Investigated protein-protein interactions between coat components and other factors.
• Analyzed the role of Golgi-associated kinase Hrr25p in coat modification.

Main Results:

• ER-derived vesicles retain their coat until reaching the Golgi.
• Golgi-associated Hrr25p phosphorylates the Sec23p/Sec24p coat complex.
• Coat phosphorylation is essential for vesicle fusion, while dephosphorylation is required for budding.
• Sec23p sequentially interacts with TRAPPI and Hrr25p to ensure directional traffic.

Conclusions:

• Coat phosphorylation by Hrr25p at the Golgi is a key step for ER-Golgi vesicle fusion.
• Sequential interactions of Sec23p regulate the directionality of vesicle transport.
• These mechanisms are conserved in mammalian cells, highlighting their fundamental importance.