title: Tubulin binding blocks mitochondrial voltage-dependent anion channel and regulates respiration.
abstract: Regulation of mitochondrial outer membrane (MOM) permeability has dual importance: in normal metabolite and energy exchange between mitochondria and cytoplasm and thus in control of respiration, and in apoptosis by release of apoptogenic factors into the cytosol. However, the mechanism of this regulation, dependent on the voltage-dependent anion channel (VDAC), the major channel of MOM, remains controversial. A long-standing puzzle is that in permeabilized cells, adenine nucleotide translocase (ANT) is less accessible to cytosolic ADP than in isolated mitochondria. We solve this puzzle by finding a missing player in the regulation of MOM permeability: the cytoskeletal protein tubulin. We show that nanomolar concentrations of dimeric tubulin induce voltage-sensitive reversible closure of VDAC reconstituted into planar phospholipid membranes. Tubulin strikingly increases VDAC voltage sensitivity and at physiological salt conditions could induce VDAC closure at <10 mV transmembrane potentials. Experiments with isolated mitochondria confirm these findings. Tubulin added to isolated mitochondria decreases ADP availability to ANT, partially restoring the low MOM permeability (high apparent K(m) for ADP) found in permeabilized cells. Our findings suggest a previously unknown mechanism of regulation of mitochondrial energetics, governed by VDAC and tubulin at the mitochondria-cytosol interface. This tubulin-VDAC interaction requires tubulin anionic C-terminal tail (CTT) peptides. The significance of this interaction may be reflected in the evolutionary conservation of length and anionic charge in CTT throughout eukaryotes, despite wide changes in the exact sequence. Additionally, tubulins that have lost significant length or anionic character are only found in cells that do not have mitochondria.
authors.affiliation: Laboratory of Physical and Structural Biology, Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA. rostovtt@mail.nih.gov
authors.forename: Tatiana K
authors.initials: TK
authors.lastname: Rostovtseva
authors.forename: Kely L
authors.initials: KL
authors.lastname: Sheldon
authors.forename: Elnaz
authors.initials: E
authors.lastname: Hassanzadeh
authors.forename: Claire
authors.initials: C
authors.lastname: Monge
authors.forename: Valdur
authors.initials: V
authors.lastname: Saks
authors.forename: Sergey M
authors.initials: SM
authors.lastname: Bezrukov
authors.forename: Dan L
authors.initials: DL
authors.lastname: Sackett
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019069:Cell Respiration / Q000502:physiology*; D004594:Electrophysiology; D019143:Evolution, Molecular; D006801:Humans; D015640:Ion Channel Gating; D008051:Lipid Bilayers / Q000737:chemistry; D008928:Mitochondria / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010085:Oxidative Phosphorylation; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats; D016415:Sequence Alignment; D014404:Tubulin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D050994:Voltage-Dependent Anion Channels / Q000235:genetics / Q000378:metabolism*
chemical_list: D008051:Lipid Bilayers; D010455:Peptides; D014404:Tubulin; D050994:Voltage-Dependent Anion Channels