Mammalian mitochondrial inner membrane fusion is mediated by optic atrophy 1 (OPA1). Under physiological conditions, OPA1 undergoes proteolytic processing to form a membrane-anchored long isoform (L-OPA1) and a soluble short isoform (S-OPA1). A combination of L-OPA1 and S-OPA1 is essential for efficient membrane fusion; however, the relevant mechanism is not well understood. In this study, we investigate the cryo-electron microscopic structures of S-OPA1–coated liposomes in nucleotide-free and GTPγS-bound states. S-OPA1 exhibits a general dynamin-like structure and can assemble onto membranes in a helical array with a dimer building block. We reveal that hydrophobic residues in its extended membrane-binding domain are critical for its tubulation activity. The binding of GTPγS triggers a conformational change and results in a rearrangement of the helical lattice and tube expansion similar to that of S-Mgm1. These observations indicate that S-OPA1 adopts a dynamin-like power stroke membrane remodeling mechanism during mitochondrial inner membrane fusion.
Cryo-EM maps of S-OPA1 196-252 coated tubes have been deposited into Electron Microscopy Data Bank with the accession codes EMD-9901 for the helical reconstruction of nucleotide-free state, EMD-9903 for the tomographic reconstruction of nucleotide-free state and EMD-9902 for the tomographic reconstruction of GTPγS bound state, respectively. Sub-tomogram averaged cryo-EM map of wild type S-OPA1 coated tubes is also deposited with the accession code of EMD-0722. The raw data of GTPase assay in this study has been included as a supporting file.
Helical reconstruction of S-OPA1 at nucleotide-free stateEMDB Protein Data Bank, EMD- 9901.
S-OPA1 coated liposome tube at GTPgamaS bound stateEMDB Protein Data Bank, EMD- 9902.
S-OPA1 coated liposome tube at nucleotide-free stateEMDB Protein Data Bank, EMD- 9903.
Full length S-OPA1 coated liposome tube at nucleotide-free stateEMDB Protein Data Bank, EMD- 0722.
Crystal structure of nucleotide-free Mgm1RCSB Protein Data Bank, 6QL4.
Structure of s-Mgm1 decorating the outer surface of tubulated lipid membranesRCSB Protein Data Bank, 6RZT.
Structure of s-Mgm1 decorating the outer surface of tubulated lipid membranes in the GTPgammaS bound stateRCSB Protein Data Bank, 6RZU.
- Yan Zhang
- Fei Sun
- Fei Sun
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Hitoshi Nakatogawa, Tokyo Institute of Technology, Japan
© 2020, Zhang et al.
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