Phospholipid Association Is Essential for Dynamin-related Protein Mgm1 to Function in Mitochondrial Membrane Fusion

• Published in: The Journal of biological chemistry Vol. 284; no. 42; pp. 28682 - 28686
• Main Authors: Rujiviphat, Jarungjit, Meglei, Gabriela, Rubinstein, John L., McQuibban, G.Angus
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 16-10-2009; American Society for Biochemistry and Molecular Biology
• Subjects: Chromatography, Gel; Circular Dichroism; Dynamins - chemistry; Enzyme-Linked Immunosorbent Assay; Fungal Proteins - chemistry; GTP Phosphohydrolases - chemistry; GTP Phosphohydrolases - metabolism; GTP-Binding Proteins - chemistry; Lipids - chemistry; Liposomes - chemistry; Membrane Fusion; Mitochondrial Membranes - metabolism; Mitochondrial Proteins - chemistry; Models, Biological; Molecular Basis of Cell and Developmental Biology; Mutation; Phospholipids - chemistry; Protein Structure, Tertiary; Saccharomyces cerevisiae Proteins - chemistry
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M109.044933

Mgm1, the yeast ortholog of mammalian OPA1, is a key component in mitochondrial membrane fusion and is required for maintaining mitochondrial dynamics and morphology. We showed recently that the purified short isoform of Mgm1 (s-Mgm1) possesses GTPase activity, self-assembles into low order oligomers, and interacts specifically with negatively charged phospholipids (Meglei, G., and McQuibban, G. A. (2009) Biochemistry 48, 1774–1784). Here, we demonstrate that s-Mgm1 binds to a mixture of phospholipids characteristic of the mitochondrial inner membrane. Binding to physiologically representative lipids results in ∼50-fold stimulation of s-Mgm1 GTPase activity. s-Mgm1 point mutants that are defective in oligomerization and lipid binding do not exhibit such stimulation and do not function in vivo. Electron microscopy and lipid turbidity assays demonstrate that s-Mgm1 promotes liposome interaction. Furthermore, s-Mgm1 assembles onto liposomes as oligomeric rings with 3-fold symmetry. The projection map of negatively stained s-Mgm1 shows six monomers, consistent with two stacked trimers. Taken together, our data identify a lipid-binding domain in Mgm1, and the structural analysis suggests a model of how Mgm1 promotes the fusion of opposing mitochondrial inner membranes.