Mouse VDAC Isoforms Expressed in Yeast: Channel Properties and Their Roles in Mitochondrial Outer Membrane Permeability |
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Authors: | X Xu W Decker MJ Sampson WJ Craigen M Colombini |
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Institution: | (1) Department of Biology, University of Maryland, College Park, MD 20742, USA, US;(2) Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA, US |
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Abstract: | The channel-forming protein called VDAC forms the major pathway in the mitochondrial outer membrane and controls metabolite
flux across that membrane. The different VDAC isoforms of a species may play different roles in the regulation of mitochondrial
functions. The mouse has three VDAC isoforms (VDAC1, VDAC2 and VDAC3). These proteins and different versions of VDAC3 were
expressed in yeast cells (S. cerevisiae) missing the major yeast VDAC gene and studied using different approaches. When reconstituted into liposomes, each isoform
induced a permeability in the liposomes with a similar molecular weight cutoff (between 3,400 and 6,800 daltons based on permeability
to polyethylene glycol). In contrast, electrophysiological studies on purified proteins showed very different channel properties.
VDAC1 is the prototypic version whose properties are highly conserved among other species. VDAC2 also has normal gating activity
but may exist in 2 forms, one with a lower conductance and selectivity. VDAC3 can also form channels in planar phospholipid
membranes. It does not insert readily into membranes and generally does not gate well even at high membrane potentials (up
to 80 mV). Isolated mitochondria exhibit large differences in their outer membrane permeability to NADH depending on which
of the mouse VDAC proteins was expressed. These differences in permeability could not simply be attributed to different amounts
of each protein present in the isolated mitochondria. The roles of these different VDAC proteins are discussed.
Received: 19 June 1998/Revised: 1 April 1999 |
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Keywords: | : Electrophysiology — Insertion — Gating — NADH — Liposomes |
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