title: Dual function of mitochondrial Nm23-H4 protein in phosphotransfer and intermembrane lipid transfer: a cardiolipin-dependent switch.
abstract: The nucleoside diphosphate kinase Nm23-H4/NDPK-D forms symmetrical hexameric complexes in the mitochondrial intermembrane space with phosphotransfer activity using mitochondrial ATP to regenerate nucleoside triphosphates. We demonstrate the complex formation between Nm23-H4 and mitochondrial GTPase OPA1 in rat liver, suggesting its involvement in local and direct GTP delivery. Similar to OPA1, Nm23-H4 is further known to strongly bind in vitro to anionic phospholipids, mainly cardiolipin, and in vivo to the inner mitochondrial membrane. We show here that such protein-lipid complexes inhibit nucleoside diphosphate kinase activity but are necessary for another function of Nm23-H4, selective intermembrane lipid transfer. Mitochondrial lipid distribution was analyzed by liquid chromatography-mass spectrometry using HeLa cells expressing either wild-type Nm23-H4 or a membrane binding-deficient mutant at a site predicted based on molecular modeling to be crucial for cardiolipin binding and transfer mechanism. We found that wild type, but not the mutant enzyme, selectively increased the content of cardiolipin in the outer mitochondrial membrane, but the distribution of other more abundant phospholipids (e.g. phosphatidylcholine) remained unchanged. HeLa cells expressing the wild-type enzyme showed increased accumulation of Bax in mitochondria and were sensitized to rotenone-induced apoptosis as revealed by stimulated release of cytochrome c into the cytosol, elevated caspase 3/7 activity, and increased annexin V binding. Based on these data and molecular modeling, we propose that Nm23-H4 acts as a lipid-dependent mitochondrial switch with dual function in phosphotransfer serving local GTP supply and cardiolipin transfer for apoptotic signaling and putative other functions.
authors.affiliation: From the Laboratory of Fundamental and Applied Bioenergetics and Federative Research Structure Environmental and Systems Biology, University Joseph Fourier, 38041 Grenoble Cedex 9, France.
authors.forename: Uwe
authors.initials: U
authors.lastname: Schlattner
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Tokarska-Schlattner
authors.forename: Sacnicte
authors.initials: S
authors.lastname: Ramirez
authors.forename: Yulia Y
authors.initials: YY
authors.lastname: Tyurina
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Amoscato
authors.forename: Dariush
authors.initials: D
authors.lastname: Mohammadyani
authors.forename: Zhentai
authors.initials: Z
authors.lastname: Huang
authors.forename: Jianfei
authors.initials: J
authors.lastname: Jiang
authors.forename: Naveena
authors.initials: N
authors.lastname: Yanamala
authors.forename: Amal
authors.initials: A
authors.lastname: Seffouh
authors.forename: Mathieu
authors.initials: M
authors.lastname: Boissan
authors.forename: Raquel F
authors.initials: RF
authors.lastname: Epand
authors.forename: Richard M
authors.initials: RM
authors.lastname: Epand
authors.forename: Judith
authors.initials: J
authors.lastname: Klein-Seetharaman
authors.forename: Marie-Lise
authors.initials: ML
authors.lastname: Lacombe
authors.forename: Valerian E
authors.initials: VE
authors.lastname: Kagan
mesh_terms: D000818:Animals; D017209:Apoptosis; D002308:Cardiolipins / Q000737:chemistry / Q000502:physiology*; D020558:GTP Phosphohydrolases / Q000737:chemistry; D007425:Intracellular Membranes / Q000378:metabolism*; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry*; D008099:Liver / Q000378:metabolism; D008297:Male; D008958:Models, Molecular; D061107:Nucleoside Diphosphate Kinase D / Q000737:chemistry* / Q000502:physiology*; D010743:Phospholipids / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002308:Cardiolipins; D008055:Lipids; D010743:Phospholipids; C517946:NME4 protein, human; D061107:Nucleoside Diphosphate Kinase D; D020558:GTP Phosphohydrolases