Phospholipid association is essential for dynamin-related protein Mgm1 to function in mitochondrial membrane fusion.
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 approximately 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.
Rujiviphat
Jarungjit
J
Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
Meglei
Gabriela
G
Rubinstein
John L
JL
McQuibban
G Angus
GA
D002850:Chromatography, Gel; D002942:Circular Dichroism; D034281:Dynamins / Q000737:chemistry*; D004797:Enzyme-Linked Immunosorbent Assay; D005656:Fungal Proteins / Q000737:chemistry; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry; D008561:Membrane Fusion; D051336:Mitochondrial Membranes / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000737:chemistry*; D008954:Models, Biological; D009154:Mutation; D010743:Phospholipids / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry*
D005656:Fungal Proteins; D008055:Lipids; D008081:Liposomes; C082883:MGM1 protein, S cerevisiae; D024101:Mitochondrial Proteins; D010743:Phospholipids; D029701:Saccharomyces cerevisiae Proteins; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D034281:Dynamins
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