Sec24 is a coincidence detector that simultaneously binds two signals to drive ER export

Area of Science:

• Cell Biology
• Protein Trafficking
• Molecular Mechanisms

Background:

• The COPII coat protein Sec24 recognizes cytosolic signals for secretory protein incorporation into ER-derived vesicles.
• Erv14/Cornichon family proteins act as cargo receptors, mediating transmembrane protein export, but their precise function remains unclear.

Purpose of the Study:

• To elucidate the molecular mechanism of Erv14 function in protein export.
• To investigate the interaction between Erv14, its clients, and the Sec24 coat protein.

Main Methods:

• Targeted mutagenesis of Erv14 to identify key residues.
• Analysis of client protein interactions with Erv14 and Sec24.
• Investigating the role of novel cargo-binding surfaces on Sec24.

Main Results:

• Conserved residues in Erv14's transmembrane domain mediate client interaction.
• Erv14 interaction with Sec24 is essential for efficient client trafficking.
• Some clients directly interact with Sec24, indicating a dual interaction mode.

Conclusions:

• Erv14 functions as a cargo receptor, coupling membrane proteins to the COPII coat.
• Maximal protein export requires a bivalent signal from both cargo and Erv14.
• Sec24 acts as a coincidence detector, binding multiple signals for efficient polytopic membrane protein packaging.