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The heptad repeat domain 1 of Mitofusin has membrane destabilization function in mitochondrial fusion.

ABSTRACT: Mitochondria are double-membrane-bound organelles that constantly change shape through membrane fusion and fission. Outer mitochondrial membrane fusion is controlled by Mitofusin, whose molecular architecture consists of an N-terminal GTPase domain, a first heptad repeat domain (HR1), two transmembrane domains, and a second heptad repeat domain (HR2). The mode of action of Mitofusin and the specific roles played by each of these functional domains in mitochondrial fusion are not fully understood. Here, using a combination of in situ and in vitro fusion assays, we show that HR1 induces membrane fusion and possesses a conserved amphipathic helix that folds upon interaction with the lipid bilayer surface. Our results strongly suggest that HR1 facilitates membrane fusion by destabilizing the lipid bilayer structure, notably in membrane regions presenting lipid packing defects. This mechanism for fusion is thus distinct from that described for the heptad repeat domains of SNARE and viral proteins, which assemble as membrane-bridging complexes, triggering close membrane apposition and fusion, and is more closely related to that of the C-terminal amphipathic tail of the Atlastin protein.

SUBMITTER: Daste F

PROVIDER: S-EPMC5989784 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature

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The heptad repeat domain 1 of Mitofusin has membrane destabilization function in mitochondrial fusion.

Daste Frédéric F Sauvanet Cécile C Bavdek Andrej A Baye James J Pierre Fabienne F Le Borgne Rémi R David Claudine C Rojo Manuel M Fuchs Patrick P Tareste David D

EMBO reports 20180416 6

Mitochondria are double-membrane-bound organelles that constantly change shape through membrane fusion and fission. Outer mitochondrial membrane fusion is controlled by Mitofusin, whose molecular architecture consists of an N-terminal GTPase domain, a first heptad repeat domain (HR1), two transmembrane domains, and a second heptad repeat domain (HR2). The mode of action of Mitofusin and the specific roles played by each of these functional domains in mitochondrial fusion are not fully understood ...[more]

PMID: 29661855

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Project description:Respiratory syncytial virus (RSV) mediates host cell entry through the fusion (F) protein, which undergoes a conformational change to facilitate the merger of viral and host lipid membrane envelopes. The RSV F protein comprises a trimer of disulfide-bonded F1 and F2 subunits that is present on the virion surface in a metastable prefusion state. This prefusion form is readily triggered to undergo refolding to bring two heptad repeats (heptad repeat A [HRA] and HRB) into close proximity to form a six-helix bundle that stabilizes the postfusion form and provides the free energy required for membrane fusion. This process can be triggered independently of other proteins. Here, we have performed a comprehensive analysis of a third heptad repeat region, HRC (amino acids 75 to 97), an amphipathic ?-helix that lies at the interface of the prefusion F trimer and is a major structural feature of the F2 subunit. We performed alanine scanning mutagenesis from Lys-75 to Met-97 and assessed all mutations in transient cell culture for expression, proteolytic processing, cell surface localization, protein conformation, and membrane fusion. Functional characterization revealed a striking distribution of activity in which fusion-increasing mutations localized to one side of the helical face, while fusion-decreasing mutations clustered on the opposing face. Here, we propose a model in which HRC plays a stabilizing role within the globular head for the prefusion F trimer and is potentially involved in the early events of triggering, prompting fusion peptide release and transition into the postfusion state.IMPORTANCE RSV is recognized as the most important viral pathogen among pediatric populations worldwide, yet no vaccine or widely available therapeutic treatment is available. The F protein is critical for the viral replication process and is the major target for neutralizing antibodies. Recent years have seen the development of prefusion stabilized F protein-based approaches to vaccine design. A detailed understanding of the specific domains and residues that contribute to protein stability and fusion function is fundamental to such efforts. Here, we present a comprehensive mutagenesis-based study of a region of the RSV F2 subunit (amino acids 75 to 97), referred to as HRC, and propose a role for this helical region in maintaining the delicate stability of the prefusion form.

Dataset Information

The heptad repeat domain 1 of Mitofusin has membrane destabilization function in mitochondrial fusion.

Publications

The heptad repeat domain 1 of Mitofusin has membrane destabilization function in mitochondrial fusion.

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