Cryo-electron tomography reveals how COPII assembles on cargo-containing membranes

Area of Science:

• Cell Biology
• Molecular Biology
• Structural Biology

Background:

• Proteins move through the eukaryotic secretory pathway via membrane trafficking.
• The coat protein complex II (COPII) facilitates anterograde transport from the endoplasmic reticulum to other organelles.
• The COPII coat's native structure and cargo-influenced morphology are not well understood.

Purpose of the Study:

• To investigate the native architecture of the COPII coat.
• To understand how cargo influences COPII carrier morphology.
• To elucidate the mechanism of spherical vesicle formation in COPII-mediated transport.

Main Methods:

• Reconstitution of COPII-coated membrane carriers using purified Saccharomyces cerevisiae proteins.
• Utilizing cell-derived microsomes as a native membrane source.
• Employing cryo-electron tomography and subtomogram averaging.

Main Results:

• COPII coat binds cargo and forms largely spherical vesicles from native membranes.
• Detailed architecture of the inner and outer COPII coat layers was revealed.
• Insights into the mechanisms generating spherical carriers and membrane curvature were obtained.

Conclusions:

• The study provides a structural understanding of the COPII coat.
• Findings advance knowledge on cargo-mediated regulation of COPII carrier formation.
• This work offers insights into membrane curvature generation during protein transport.