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MBE Advance Access published online on December 17, 2008
Molecular Biology and Evolution, 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 Article

The single mitochondrial porin of Trypanosoma brucei is the main metabolite transporter in the outer mitochondrial membrane

Mascha Pusnik1), Fabien Charrière1), Pascal Mäser2), Ross Waller3), Michael J. Dagley4), Trevor Lithgow4) and André Schneider1)

1) Department of Chemistry and Biochemistry, University of Bern, Freiestr. 3, CH-3012 Bern, Switzerland
2) Institute of Cell Biology, University of Bern, Baltzerstrasse 4, CH-3012 Bern, Switzerland
3) School of Botany, University of Melbourne, Parkville 3010, Australia
4) Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, 30 Flemington Road, Parkville 3010, Australia

Received for publication October 15, 2008. Revision received December 12, 2008. Accepted for publication December 12, 2008.

All mitochondria have integral outer membrane proteins with β-barrel structures including the conserved metabolite transporter VDAC 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 knock-out cells did not produce 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 knock-out 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


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