Structural basis for Vipp1 membrane binding: from loose coats and carpets to ring and rod assemblies

Area of Science:

• Molecular biology
• Cell biology
• Structural biology

Background:

• Vesicle-inducing protein in plastids 1 (Vipp1) is crucial for thylakoid membrane formation and upkeep.
• Vipp1 belongs to the endosomal sorting complexes required for transport III (ESCRT-III) superfamily, but its membrane remodeling mechanism remains unclear.

Purpose of the Study:

• To elucidate the structural mechanisms by which Vipp1 remodels membranes.
• To understand Vipp1's role in membrane curvature, tubulation, and fusion.

Main Methods:

• Cryo-electron microscopy (cryo-EM) and subtomogram averaging were used to determine structures of Vipp1 interacting with lipid membranes.
• Analysis of N-terminally truncated Vipp1 mutants and a conformation-restrained Vipp1 mutant.

Main Results:

• Cryo-EM revealed helical and stacked-ring assemblies of Vipp1 engulfing membranes, and carpet structures covering lipid vesicles.
• Helix α0 was identified as the membrane-anchoring domain essential for membrane tubulation.
• High-resolution structures revealed molecular details of membrane anchoring and intersubunit contacts.
• Vipp1 undergoes membrane curvature-dependent structural transitions, from carpets to rings and rods.

Conclusions:

• Vipp1 utilizes distinct structural assemblies (carpets, rings, rods) to remodel membranes.
• Helix α0 plays a critical role in anchoring Vipp1 and inducing membrane curvature.
• These structural dynamics facilitate membrane fusion, crucial for thylakoid biogenesis.