Cryo-EM structures of S-OPA1 reveal its interactions with membrane and changes upon nucleotide binding

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.

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Cryo-EM structures reveal a conformational change of SOPA1 during mitochondrial inner membrane fusion

10.1101/528042 ◽

2019 ◽

Cited By ~ 2

Author(s):

Danyang Zhang ◽

Yan Zhang ◽

Jun Ma ◽

Tongxin Niu ◽

Wenbo Chen ◽

...

Keyword(s):

Membrane Fusion ◽

Bound States ◽

General Structure ◽

Proteolytic Processing ◽

Gtpase Domain ◽

Inner Membrane ◽

Unique Role ◽

Mitochondrial Inner Membrane ◽

Membrane Tubulation

ABSTRACTMammalian mitochondrial inner membrane fusion is mediated by OPA1(optic atrophy 1). Under physiological condition, OPA1 undergoes proteolytic processing to form a membrane-anchored long isoform (LOPA1) and a soluble short isoform (SOPA1). A combination of LOPA1 and SOPA1 are required for membrane fusion, however, the relevant mechanism is not well understood. In this study, we investigate the cryo-EM structures of SOPA1 coated liposome tube at nucleotide-free and GTPγS bound states. SOPA1 exhibits a general structure of dynamin family and can assemble onto membrane in a helical array with a building block of dimer and thus induce membrane tubulation. A predicted amphipathic helix is discovered to mediate the tubulation activity of SOPA1. The binding of GTPγS causes a conformational rotation between GTPase domain and stalk region, and then induces a rearrangement of the helical array and an expansion of the tube, which is opposite to the behavior of other dynamin proteins, suggesting a unique role of SOPA1 in the fusion of mitochondrial inner membrane.

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Liposome-mitochondrial inner membrane fusion. Lateral diffusion of integral electron transfer components.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(19)85768-x ◽

1980 ◽

Vol 255 (8) ◽

pp. 3748-3756 ◽

Cited By ~ 2

Author(s):

H. Schneider ◽

J.J. Lemasters ◽

M. Höchli ◽

C.R. Hackenbrock

Keyword(s):

Electron Transfer ◽

Membrane Fusion ◽

Lateral Diffusion ◽

Inner Membrane ◽

Mitochondrial Inner Membrane

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The essential yeast protein MIM44 (encoded by MPI1) is involved in an early step of preprotein translocation across the mitochondrial inner membrane.

Molecular and Cellular Biology ◽

10.1128/mcb.13.12.7364 ◽

1993 ◽

Vol 13 (12) ◽

pp. 7364-7371 ◽

Cited By ~ 76

Author(s):

J Blom ◽

M Kübrich ◽

J Rassow ◽

W Voos ◽

P J Dekker ◽

...

Keyword(s):

Protein Import ◽

Early Stage ◽

Proteolytic Processing ◽

Early Step ◽

Direct Role ◽

Inner Membrane ◽

Mitochondrial Inner Membrane ◽

Preprotein Translocation ◽

In Transit

The essential yeast gene MPI1 encodes a mitochondrial membrane protein that is possibly involved in protein import into the organelle (A. C. Maarse, J. Blom, L. A. Grivell, and M. Meijer, EMBO J. 11:3619-3628, 1992). For this report, we determined the submitochondrial location of the MPI1 gene product and investigated whether it plays a direct role in the translocation of preproteins. By fractionation of mitochondria, the mature protein of 44 kDa was localized to the mitochondrial inner membrane and therefore termed MIM44. Import of the precursor of MIM44 required a membrane potential across the inner membrane and involved proteolytic processing of the precursor. A preprotein in transit across the mitochondrial membranes was cross-linked to MIM44, whereas preproteins arrested on the mitochondrial surface or fully imported proteins were not cross-linked. When preproteins were arrested at two distinct stages of translocation across the inner membrane, only preproteins at an early stage of translocation could be cross-linked to MIM44. Moreover, solubilized MIM44 was found to interact with in vitro-synthesized preproteins. We conclude that MIM44 is a component of the mitochondrial inner membrane import machinery and interacts with preproteins in an early step of translocation.

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Coassembly of Mgm1 isoforms requires cardiolipin and mediates mitochondrial inner membrane fusion

The Journal of Cell Biology ◽

10.1083/jcb.200906098 ◽

2009 ◽

Vol 186 (6) ◽

pp. 793-803 ◽

Cited By ~ 194

Author(s):

Rachel M. DeVay ◽

Lenin Dominguez-Ramirez ◽

Laura L. Lackner ◽

Suzanne Hoppins ◽

Henning Stahlberg ◽

...

Keyword(s):

Membrane Fusion ◽

Coiled Coil ◽

Intermembrane Space ◽

Dependent Manner ◽

Related Protein ◽

Mitochondrial Membranes ◽

Inner Membrane ◽

Mitochondrial Inner Membrane ◽

N Terminus ◽

In Trans

Two dynamin-related protein (DRP) families are essential for fusion of the outer and inner mitochondrial membranes, Fzo1 (yeast)/Mfn1/Mfn2 (mammals) and Mgm1 (yeast)/Opa1 (mammals), respectively. Fzo1/Mfns possess two medial transmembrane domains, which place their critical GTPase and coiled-coil domains in the cytosol. In contrast, Mgm1/Opa1 are present in cells as long (l) isoforms that are anchored via the N terminus to the inner membrane, and short (s) isoforms were predicted to be soluble in the intermembrane space. We addressed the roles of Mgm1 isoforms and how DRPs function in membrane fusion. Our analysis indicates that in the absence of a membrane, l- and s-Mgm1 both exist as inactive GTPase monomers, but that together in trans they form a functional dimer in a cardiolipin-dependent manner that is the building block for higher-order assemblies.

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