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MBE Advance Access originally published online on December 17, 2008
Molecular Biology and Evolution 2009 26(3):671-680; doi:10.1093/molbev/msn288
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© The Author 2008. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Research Articles

The Single Mitochondrial Porin of Trypanosoma brucei is the Main Metabolite Transporter in the Outer Mitochondrial Membrane

Mascha Pusnik*, Fabien Charrière*, Pascal Mäser{dagger}, Ross F. Waller{ddagger}, Michael J. Dagley§, Trevor Lithgow§ and André Schneider*

* Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
{dagger} Institute of Cell Biology, University of Bern, Bern, Switzerland
{ddagger} School of Botany, University of Melbourne, Parkville, Australia
§ Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Australia

E-mail: andre.schneider{at}ibc.unibe.ch.

Accepted for publication December 12, 2008.

All mitochondria have integral outer membrane proteins with β-barrel structures including the conserved metabolite transporter VDAC (voltage dependent anion channel) and the conserved protein import channel Tom40. Bioinformatic searches of the Trypanosoma brucei genome for either VDAC or Tom40 identified a single open reading frame, with sequence analysis suggesting that VDACs and Tom40s are ancestrally related and should be grouped into the same protein family: the mitochondrial porins. The single T. brucei mitochondrial porin is essential only under growth conditions that depend on oxidative phosphorylation. Mitochondria isolated from homozygous knockout cells did not produce adenosine-triphosphate (ATP) in response to added substrates, but ATP production was restored by physical disruption of the outer membrane. These results demonstrate that the mitochondrial porin identified in T. brucei is the main metabolite channel in the outer membrane and therefore the functional orthologue of VDAC. No distinct Tom40 was identified in T. brucei. In addition to mitochondrial proteins, T. brucei imports all mitochondrial tRNAs from the cytosol. Isolated mitochondria from the VDAC knockout cells import tRNA as efficiently as wild-type. Thus, unlike the scenario in plants, VDAC is not required for mitochondrial tRNA import in T. brucei.

Key Words: mitochondrial porin • VDAC • mitochondrial protein import • Tom40 • mitochondrial tRNA import • Trypanosoma brucei

Martin Embley, Associate Editor


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