Cryo-EM structures of S-OPA1 reveal its interactions with membrane and changes upon nucleotide binding
- Chinese Academy of Sciences, China
Abstract
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.
Data availability
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.
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Helical reconstruction of S-OPA1 at nucleotide-free stateEMDB Protein Data Bank, EMD- 9901.
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S-OPA1 coated liposome tube at GTPgamaS bound stateEMDB Protein Data Bank, EMD- 9902.
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S-OPA1 coated liposome tube at nucleotide-free stateEMDB Protein Data Bank, EMD- 9903.
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Full length S-OPA1 coated liposome tube at nucleotide-free stateEMDB Protein Data Bank, EMD- 0722.
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Crystal structure of nucleotide-free Mgm1RCSB Protein Data Bank, 6QL4.
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Structure of s-Mgm1 decorating the outer surface of tubulated lipid membranesRCSB Protein Data Bank, 6RZT.
Article and author information
Author details
Funding
National Natural Science Foundation of China (31770794)
- Yan Zhang
Chinese Academy of Sciences (XDB08030202)
- Fei Sun
Ministry of Science and Technology of the People's Republic of China (2017YFA0504700)
- Fei Sun
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Reviewing Editor
- Hitoshi Nakatogawa, Tokyo Institute of Technology, Japan
Version history
- Received: July 17, 2019
- Accepted: March 30, 2020
- Accepted Manuscript published: March 31, 2020 (version 1)
- Version of Record published: April 14, 2020 (version 2)
Copyright
© 2020, Zhang et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Cryo-EM structures of S-OPA1 reveal its interactions with membrane and changes upon nucleotide binding
eLife 9:e50294.
https://doi.org/10.7554/eLife.50294
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Bacteria utilize various strategies to prevent internal dehydration during hypertonic stress. A common approach to countering the effects of the stress is to import compatible solutes such as glycine betaine, leading to simultaneous passive water fluxes following the osmotic gradient. OpuA from Lactococcus lactis is a type I ABC-importer that uses two substrate-binding domains (SBDs) to capture extracellular glycine betaine and deliver the substrate to the transmembrane domains for subsequent transport. OpuA senses osmotic stress via changes in the internal ionic strength and is furthermore regulated by the 2nd messenger cyclic-di-AMP. We now show, by means of solution-based single-molecule FRET and analysis with multi-parameter photon-by-photon hidden Markov modeling, that the SBDs transiently interact in an ionic strength-dependent manner. The smFRET data are in accordance with the apparent cooperativity in transport and supported by new cryo-EM data of OpuA. We propose that the physical interactions between SBDs and cooperativity in substrate delivery are part of the transport mechanism.
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