Combinatorial multivalent interactions drive cooperative assembly of the COPII coat

Area of Science:

• Cell biology
• Molecular and structural biology

Background:

• Protein secretion is a fundamental cellular process.
• The COPII (coat protein complex II) coat initiates vesicle formation at the endoplasmic reticulum.
• Understanding COPII coat assembly is crucial for deciphering intracellular transport.

Purpose of the Study:

• To investigate the mechanisms of COPII coat assembly.
• To elucidate how cargo-bound inner coat layers interact with the outer scaffolding layer.
• To understand how these interactions drive membrane curvature and vesicle formation.

Main Methods:

• Biochemical and biophysical analyses of protein-protein interactions.
• Structural studies of the COPII coat components, particularly Sec31.
• Mutational analysis to probe the function of intrinsically disordered regions.

Main Results:

• An intrinsically disordered region of Sec31 mediates binding to the inner coat layer through multiple interfaces.
• A newly identified charge-based interaction contributes to coat assembly.
• These multivalent interactions combinatorially reinforce coat oligomerization and scaffold stability.

Conclusions:

• The Sec31 disordered region acts as a multimodal assembly platform.
• This platform allows for plastic and evolutionarily adaptable binding interfaces.
• This mechanism explains the formation of a robust yet transient scaffold for vesicle traffic.