Two forms of Opa1 cooperate to complete fusion of the mitochondrial inner-membrane.

Yifan Ge,Sivakumar Boopathy,Julie Mcdonald,Luke H Chao,Adam W Smith,Xiaojun Shi

doi:10.7554/elife.50973

Yifan Ge, Sivakumar Boopathy + Show 4 more

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https://doi.org/10.7554/elife.50973

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Journal: eLife	Publication Date: Jan 10, 2020
Citations: 103	License type: CC BY 4.0

Affiliation: Massachusetts General Hospital, University of Akron

Abstract

Mitochondrial membrane dynamics is a cellular rheostat that relates metabolic function and organelle morphology. Using an in vitro reconstitution system, we describe a mechanism for how mitochondrial inner-membrane fusion is regulated by the ratio of two forms of Opa1. We found that the long-form of Opa1 (l-Opa1) is sufficient for membrane docking, hemifusion and low levels of content release. However, stoichiometric levels of the processed, short form of Opa1 (s-Opa1) work together with l-Opa1 to mediate efficient and fast membrane pore opening. Additionally, we found that excess levels of s-Opa1 inhibit fusion activity, as seen under conditions of altered proteostasis. These observations describe a mechanism for gating membrane fusion.

Highlights

Mitochondrial membrane fission and fusion is essential for generating a dynamic mitochondrial network and regenerative partitioning of damaged components via mitophagy (Hoppins et al, 2007)
Our experiments suggest different assembled forms of Opa1 represent functional intermediates along the membrane fusion reaction coordinate, each of which can be a checkpoint for membrane fusion and remodeling
We show that s-Opa1 alone is sufficient to mediate membrane tethering but is unable to dock and merge lipids in the two bilayers, and insufficient for hemifusion (Figure 7A)

Summary

Introduction

Mitochondrial membrane fission and fusion is essential for generating a dynamic mitochondrial network and regenerative partitioning of damaged components via mitophagy (Hoppins et al, 2007). Mitochondrial membrane fusion in metazoans is catalyzed by the mitofusins (Mfn1/2) and Opa (the outer and inner membrane fusogens, respectively), which are members of the dynamin family of large GTPases (Chen et al, 2003; Alexander et al, 2000) (Figure 1A). Outer membrane fusion requires Mfn1/2, while inner-membrane fusion requires Opa. Loss of Opa function results in a fragmented mitochondrial network, loss of mitochondrial DNA, and loss of respiratory function (MacVicar and Langer, 2016; Olichon et al, 2003). Mutations in Opa account for over a third of the identified cases of this form of childhood blindness (Pesch et al, 2001)

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