title: Phospholipid association is essential for dynamin-related protein Mgm1 to function in mitochondrial membrane fusion.
abstract: 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.
authors.affiliation: Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: Jarungjit
authors.initials: J
authors.lastname: Rujiviphat
authors.forename: Gabriela
authors.initials: G
authors.lastname: Meglei
authors.forename: John L
authors.initials: JL
authors.lastname: Rubinstein
authors.forename: G Angus
authors.initials: GA
authors.lastname: McQuibban
mesh_terms: 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*
chemical_list: 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
references.citation: J Struct Biol. 1996 Jan-Feb;116(1):9-16
references.pmid: 8742717
references.citation: Dis Model Mech. 2008 Sep-Oct;1(2-3):168-74; discussion 173
references.pmid: 19048081
references.citation: J Biol Chem. 2003 Jul 25;278(30):27781-8
references.pmid: 12707284
references.citation: J Struct Biol. 2007 Jan;157(1):64-72
references.pmid: 17055742
references.citation: Methods Cell Biol. 2008;88:237-56
references.pmid: 18617037
references.citation: Annu Rev Genet. 2005;39:503-36
references.pmid: 16285870
references.citation: Biochemistry. 2009 Mar 3;48(8):1774-84
references.pmid: 19236101
references.citation: Nat Rev Mol Cell Biol. 2004 Feb;5(2):133-47
references.pmid: 15040446
references.citation: Annu Rev Biochem. 2007;76:751-80
references.pmid: 17362197
references.citation: Biochim Biophys Acta. 1997 Sep 4;1348(1-2):207-13
references.pmid: 9370335
references.citation: Anal Biochem. 2008 Jun 1;377(1):83-8
references.pmid: 18342614
references.citation: Trends Cell Biol. 2002 Apr;12(4):178-84
references.pmid: 11978537
references.citation: FEBS Lett. 2009 Jul 7;583(13):2237-43
references.pmid: 19505460
references.citation: Nature. 2003 May 29;423(6939):537-41
references.pmid: 12774122
references.citation: Dis Model Mech. 2009 Jul-Aug;2(7-8):336-40
references.pmid: 19553694