title: Molecular and functional characterization of VDAC2 purified from mammal spermatozoa.
abstract: VDAC (voltage-dependent anion channel) is the pore-forming protein located in the outer mitochondrial membrane. In higher eukaryotes, three genes encode VDAC. Nevertheless, the knowledge of VDAC isoforms is mainly restricted to VDAC1, the only isoform that has been characterized from living tissues to date. We have highly enriched the isoform VDAC2 using as starting material bovine spermatozoa. VDAC2 was obtained in the hydroxyapatite/celite pass-through of sperm proteins solubilized with Triton X-100. This fraction showed in SDS/PAGE two major bands and one faint band in the molecular mass range of 30-35 kDa. Two-dimensional electrophoresis resolved these bands in ten spots with various Coomassie Blue staining intensities. Western-blot analysis with antibodies monospecific for each isoform and MS peptide sequencing showed that the main protein resolved in electrophoresis was VDAC2 with minor contaminations of the other isoforms. Proteomic analysis of the higher molecular mass VDAC2 protein allowed the coverage of the whole protein with the exception of the tripeptide A24AR26. In the same material, the presence of two possible amino acid substitutions (T88 to L88 and A97 to Q97) was revealed. Reconstitution of VDAC2 pores in planar lipid bilayers showed typical features of mitochondrial porins. Stepwise increases in membrane conductance were observed with a predominant conductance of approx. 3.5 nS (nanoSiemens) in 1 M KCl. Very often, small short-lived fluctuations were observed with single-channel conductance of approx. 1.5 nS. Bovine spermatozoa VDAC2 was anion selective and showed voltage dependence. The present study is the first work to report the purification and characterization of VDAC2 from a mammalian tissue.
authors.affiliation: Center of Dermatology and Andrology, Justus Liebig University of Giessen, Gaffkystrasse 14, DE 35392, Germany.
authors.forename: Viviana A
authors.initials: VA
authors.lastname: Menzel
authors.forename: M Carolina
authors.initials: MC
authors.lastname: Cassará
authors.forename: Roland
authors.initials: R
authors.lastname: Benz
authors.forename: Vito
authors.initials: V
authors.lastname: de Pinto
authors.forename: Angela
authors.initials: A
authors.lastname: Messina
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Cunsolo
authors.forename: Rosaria
authors.initials: R
authors.lastname: Saletti
authors.forename: Klaus-Dieter
authors.initials: KD
authors.lastname: Hinsch
authors.forename: Elvira
authors.initials: E
authors.lastname: Hinsch
mesh_terms: D000595:Amino Acid Sequence / Q000502:physiology; D019943:Amino Acid Substitution / Q000502:physiology; D000818:Animals; D001483:Base Sequence / Q000502:physiology; D015153:Blotting, Western; D002417:Cattle; D004591:Electrophoresis, Polyacrylamide Gel; D015640:Ion Channel Gating / Q000502:physiology; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000502:physiology; D008928:Mitochondria / Q000378:metabolism* / Q000648:ultrastructure; D051336:Mitochondrial Membranes / Q000378:metabolism* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D008970:Molecular Weight; D020033:Protein Isoforms / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013094:Spermatozoa / Q000378:metabolism* / Q000648:ultrastructure; D050996:Voltage-Dependent Anion Channel 2 / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D050996:Voltage-Dependent Anion Channel 2