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Published on: April 16, 2019
The Fusion Activity of IM30 Rings Involves Controlled Unmasking of the Fusogenic Core
Adrien Thurotte1, Dirk Schneider1
1Institute of Pharmacy and Biochemistry, Johannes Gutenberg University, Mainz, Germany.
Abstract:
The inner membrane-associated protein of 30 kDa (IM30, also known as Vipp1) is required for thylakoid membrane biogenesis and maintenance in cyanobacteria and chloroplasts. The protein forms large rings of ∼2 MDa and triggers membrane fusion in presence of Mg2+. Based on the here presented observations, IM30 rings are built from dimers of dimers, and formation of these tetrameric building blocks is driven by interactions of the central coiled-coil, formed by helices 2 and 3, and stabilized via additional interactions mainly involving helix 1. Furthermore, helix 1 as well as C-terminal regions of IM30 together negatively regulate ring-ring contacts. We propose that IM30 rings represent the inactive form of IM30, and upon binding to negatively charged membrane surfaces, the here identified fusogenic core of IM30 rings eventually interacts with the lipid bilayer, resulting in membrane destabilization and membrane fusion. Unmasking of the IM30 fusogenic core likely is controlled by Mg2+, which triggers rearrangement of the IM30 ring structure.
Insights
Inner membrane protein IM30 (Vipp1) forms large rings essential for thylakoid biogenesis. These rings, composed of tetrameric units, mediate membrane fusion, with Mg2+ controlling their activity.
Area of Science:
- Cell biology
- Protein structure and function
- Membrane biophysics
Background:
- Inner membrane-associated protein of 30 kDa (IM30), also known as Vipp1, is crucial for thylakoid membrane formation and stability in cyanobacteria and chloroplasts.
- IM30 self-assembles into large ring structures (approximately 2 MDa) and is implicated in membrane fusion processes.
Purpose of the Study:
- To elucidate the quaternary structure of IM30 rings and the molecular mechanisms underlying their role in membrane fusion.
- To investigate the role of specific protein regions and Mg2+ in regulating IM30 ring assembly and function.
Main Methods:
- Structural analysis of IM30 ring formation.
- Biochemical assays to study protein-protein interactions and membrane fusion.
- Investigating the effect of Mg2+ on IM30 structure and activity.
Main Results:
- IM30 rings are assembled from tetrameric building blocks (dimers of dimers), primarily through interactions involving helices 1, 2, and 3.
- Helix 1 and C-terminal regions negatively regulate inter-ring contacts, suggesting a mechanism for controlling ring assembly.
- A fusogenic core within the IM30 ring is proposed to interact with lipid bilayers, promoting membrane destabilization and fusion, a process likely regulated by Mg2+.
Conclusions:
- The study reveals the detailed structure of IM30 rings, identifying tetrameric units and key interaction domains.
- IM30 rings are proposed to be an inactive form, with Mg2+ triggering conformational changes that expose a fusogenic core for membrane fusion.
- These findings provide critical insights into the mechanism of thylakoid biogenesis and membrane dynamics mediated by IM30.
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