title: Recombinant human voltage dependent anion selective channel isoform 3 (hVDAC3) forms pores with a very small conductance.
abstract: OBJECTIVE
  Voltage-dependent anion channels (VDAC), also known as eukaryotic porins, are located in the outer mitochondrial membrane and allow the flux of ions and small metabolites. While the pore-forming ability of recombinant VDAC1 and VDAC2 has been extensively studied during the last decades, a clear-cut ion conducting channel activity has not been assigned to the VDAC3 isoform. Methods : Electrophysiological characterization of the recombinant protein purified and refolded was obtained after incorporation into planar lipid bilayers.
  
  
  RESULTS
  Here we report for the first time that recombinant hVDAC3, upon expression in E.coli and purification-refolding, shows a channel activity with a very small conductance (90 pS in 1 M KCl) with respect to the conductance of hVDAC1 (>3500 pS in 1 M KCl). Purified hVDAC3 allowed the passage of both chloride and gluconate anions and did not distinguish between potassium, sodium and calcium used as cations. In contrast to VDAC1, the channel was active also at transmembrane voltages higher than +/-40 mV and displayed a relatively high open probability even at +/-80 mV. hVDAC3 was only slightly voltage-dependent, displaying a tendency to adopt lower-conductance states at positive voltages applied to the cis chamber. In accordance with the small conductance of the pore, expression of hVDAC3 in a porin-less yeast strain allowed only partial recovery of the growth under non-permissive conditions.
  
  
  CONCLUSIONS
  The observed electrophysiological properties of hVDAC3 are surprisingly different from the other isoforms and are discussed in relation to the proposed physiological role of the protein in mammalian cells.
authors.affiliation: Department of Biology, University of Padova, Padova, Italy.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Checchetto
authors.forename: Simona
authors.initials: S
authors.lastname: Reina
authors.forename: Andrea
authors.initials: A
authors.lastname: Magrì
authors.forename: Ildikò
authors.initials: I
authors.lastname: Szabo
authors.forename: Vito
authors.initials: V
authors.lastname: De Pinto
mesh_terms: D003460:Crystallization; D006801:Humans; D008564:Membrane Potentials; D033681:Mitochondrial Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D019906:Nuclear Magnetic Resonance, Biomolecular; D018272:Porins / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D050994:Voltage-Dependent Anion Channels / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology
chemical_list: D033681:Mitochondrial Membrane Transport Proteins; D018272:Porins; D011994:Recombinant Proteins; C494768:VDAC3 protein, human; D050994:Voltage-Dependent Anion Channels