title: Motifs of VDAC2 required for mitochondrial Bak import and tBid-induced apoptosis.
abstract: Voltage-dependent anion channel (VDAC) proteins are major components of the outer mitochondrial membrane. VDAC has three isoforms with >70% sequence similarity and redundant roles in metabolite and ion transport. However, only Vdac2(-/-) (V2(-/-)) mice are embryonic lethal, indicating a unique and fundamental function of VDAC2 (V2). Recently, a specific V2 requirement was demonstrated for mitochondrial Bak import and truncated Bid (tBid)-induced apoptosis. To determine the relevant domain(s) of V2 involved, VDAC1 (V1) and V2 chimeric constructs were created and used to rescue V2(-/-) fibroblasts. Surprisingly, the commonly cited V2-specific N-terminal extension and cysteines were found to be dispensable for Bak import and high tBid sensitivity. In gain-of-function studies, V2 (123-179) was the minimal sequence sufficient to render V1 competent to support Bak insertion. Furthermore, in loss-of-function experiments, T168 and D170 were identified as critical residues. These motifs are conserved in zebrafish V2 (zfV2) that also rescued V2-deficient fibroblasts. Because high-resolution structures of zfV2 and mammalian V1 have become available, we could superimpose these structures and recognized that the critical V2-specific residues help to create a distinctive open "pocket" on the cytoplasmic surface that could facilitate Bak recruitment.
authors.affiliation: MitoCare Center for Mitochondrial Imaging Research and Diagnostics, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107;
authors.forename: Shamim
authors.initials: S
authors.lastname: Naghdi
authors.affiliation: Department of Physiology, Faculty of Medicine, Semmelweis University, Budapest 1094, Hungary.
authors.forename: Péter
authors.initials: P
authors.lastname: Várnai
authors.affiliation: MitoCare Center for Mitochondrial Imaging Research and Diagnostics, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107; gyorgy.hajnoczky@jefferson.edu.
authors.forename: György
authors.initials: G
authors.lastname: Hajnóczky
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D051023:BH3 Interacting Domain Death Agonist Protein / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology; D050996:Voltage-Dependent Anion Channel 2 / Q000235:genetics / Q000378:metabolism*; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: C494772:BAK1 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494773:Bak1 protein, mouse; C494765:VDAC2 protein, human; C494766:Vdac2 protein, mouse; D050996:Voltage-Dependent Anion Channel 2; D050998:bcl-2 Homologous Antagonist-Killer Protein
keywords: Bak; VDAC2; apoptosis; mitochondria; tBid