Bacterial Origin of a Mitochondrial Outer Membrane Protein Translocase

Background: The archaic translocase of the outer mitochondrial membrane (ATOM) from Trypanosoma brucei mediates protein import. Results: ATOM forms a hydrophilic transmembrane pore with channel characteristics resembling bacterial-type protein translocases. Conclusion: ATOM descended from a bacterial porin and represents an evolutionary intermediate. Significance: ATOM presumably represents the missing link between the mitochondrial outer membrane protein import pore and its bacterial ancestors. Mitochondria are of bacterial ancestry and have to import most of their proteins from the cytosol. This process is mediated by Tom40, an essential protein that forms the protein-translocating pore in the outer mitochondrial membrane. Tom40 is conserved in virtually all eukaryotes, but its evolutionary origin is unclear because bacterial orthologues have not been identified so far. Recently, it was shown that the parasitic protozoon Trypanosoma brucei lacks a conventional Tom40 and instead employs the archaic translocase of the outer mitochondrial membrane (ATOM), a protein that shows similarities to both eukaryotic Tom40 and bacterial protein translocases of the Omp85 family. Here we present electrophysiological single channel data showing that ATOM forms a hydrophilic pore of large conductance and high open probability. Moreover, ATOM channels exhibit a preference for the passage of cationic molecules consistent with the idea that it may translocate unfolded proteins targeted by positively charged N-terminal presequences. This is further supported by the fact that the addition of a presequence peptide induces transient pore closure. An in-depth comparison of these single channel properties with those of other protein translocases reveals that ATOM closely resembles bacterial-type protein export channels rather than eukaryotic Tom40. Our results support the idea that ATOM represents an evolutionary intermediate between a bacterial Omp85-like protein export machinery and the conventional Tom40 that is found in mitochondria of other eukaryotes.

[1]  E. Schleiff,et al.  Identification of two voltage-dependent anion channel-like protein sequences conserved in Kinetoplastida , 2012, Biology Letters.

[2]  P. Doležal,et al.  Tom40 is likely common to all mitochondria , 2012, Current Biology.

[3]  V. Mootha,et al.  Evolutionary Diversity of the Mitochondrial Calcium Uniporter , 2012, Science.

[4]  Sri H. Ramarathinam,et al.  Discovery of an archetypal protein transport system in bacterial outer membranes , 2012, Nature Structural &Molecular Biology.

[5]  P. Bütikofer,et al.  An essential bacterial-type cardiolipin synthase mediates cardiolipin formation in a eukaryote , 2012, Proceedings of the National Academy of Sciences.

[6]  S. Nussberger,et al.  Protein translocation through Tom40: kinetics of peptide release. , 2012, Biophysical journal.

[7]  M. Parsons Faculty Opinions recommendation of Mitochondrial preprotein translocase of trypanosomatids has a bacterial origin. , 2011 .

[8]  J. Palenchar,et al.  The characterization of a unique Trypanosoma brucei β-hydroxybutyrate dehydrogenase. , 2011, Molecular and biochemical parasitology.

[9]  Anke Harsman,et al.  Exploring protein import pores of cellular organelles at the single molecule level using the planar lipid bilayer technique. , 2011, European journal of cell biology.

[10]  T. Lithgow,et al.  Minor modifications and major adaptations: the evolution of molecular machines driving mitochondrial protein import. , 2011, Biochimica et biophysica acta.

[11]  Anke Harsman,et al.  Protein conducting nanopores , 2010, Journal of physics. Condensed matter : an Institute of Physics journal.

[12]  T. Cavalier-smith Kingdoms Protozoa and Chromista and the eozoan root of the eukaryotic tree , 2010, Biology Letters.

[13]  O. Kepp,et al.  Bacterial Porin Disrupts Mitochondrial Membrane Potential and Sensitizes Host Cells to Apoptosis , 2009, PLoS pathogens.

[14]  Hammad Naveed,et al.  Predicting weakly stable regions, oligomerization state, and protein–protein interfaces in transmembrane domains of outer membrane proteins , 2009, Proceedings of the National Academy of Sciences.

[15]  D. Bhattacharya,et al.  Mitochondrial and plastid evolution in eukaryotes: an outsiders' perspective , 2009, Nature Reviews Genetics.

[16]  Michael J. Dagley,et al.  The single mitochondrial porin of Trypanosoma brucei is the main metabolite transporter in the outer mitochondrial membrane. , 2008, Molecular biology and evolution.

[17]  A. Delcour,et al.  The TpsB Translocator HMW1B of Haemophilus influenzae Forms a Large Conductance Channel* , 2008, Journal of Biological Chemistry.

[18]  B. Clantin,et al.  Structure of the Membrane Protein FhaC: A Member of the Omp85-TpsB Transporter Superfamily , 2007, Science.

[19]  A. von Haeseler,et al.  Functional and Phylogenetic Properties of the Pore-forming β-Barrel Transporters of the Omp85 Family* , 2007, Journal of Biological Chemistry.

[20]  T. Cavalier-smith Origin of mitochondria by intracellular enslavement of a photosynthetic purple bacterium , 2006, Proceedings of the Royal Society B: Biological Sciences.

[21]  T. Lithgow,et al.  Evolution of the Molecular Machines for Protein Import into Mitochondria , 2006, Science.

[22]  B. Clantin,et al.  Channel Properties of TpsB Transporter FhaC Point to Two Functional Domains with a C-terminal Protein-conducting Pore* , 2006, Journal of Biological Chemistry.

[23]  R. Casadio,et al.  Preprotein translocase of the outer mitochondrial membrane: reconstituted Tom40 forms a characteristic TOM pore. , 2005, Journal of molecular biology.

[24]  T. Becker,et al.  The Evolutionarily Related β-Barrel Polypeptide Transporters from Pisum sativum and Nostoc PCC7120 Contain Two Distinct Functional Domains* , 2005, Journal of Biological Chemistry.

[25]  D. W. Staple,et al.  Solution structure and thermodynamic investigation of the HIV-1 frameshift inducing element. , 2005, Journal of molecular biology.

[26]  Patricia J. Johnson,et al.  Ancient Invasions: From Endosymbionts to Organelles , 2004, Science.

[27]  W. Kühlbrandt,et al.  Characterization of the translocon of the outer envelope of chloroplasts , 2003, The Journal of cell biology.

[28]  J. Herrmann Converting bacteria to organelles: evolution of mitochondrial protein sorting. , 2003, Trends in microbiology.

[29]  W. Im,et al.  Ion permeation and selectivity of OmpF porin: a theoretical study based on molecular dynamics, Brownian dynamics, and continuum electrodiffusion theory. , 2002, Journal of molecular biology.

[30]  J. Soll,et al.  The chloroplast protein import channel Toc75: pore properties and interaction with transit peptides. , 2002, Biophysical journal.

[31]  E. Willery,et al.  Channel Formation by FhaC, the Outer Membrane Protein Involved in the Secretion of the Bordetella pertussis Filamentous Hemagglutinin* , 1999, The Journal of Biological Chemistry.

[32]  P. Phale,et al.  Brownian dynamics simulation of ion flow through porin channels. , 1999, Journal of molecular biology.

[33]  A. Schulz,et al.  Origin of a chloroplast protein importer. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[34]  W. Neupert,et al.  The Isolated Complex of the Translocase of the Outer Membrane of Mitochondria , 1998, Journal of Biological Chemistry.

[35]  K. Dietmeier,et al.  Tom40 forms the hydrophilic channel of the mitochondrial import pore for preproteins , 1998, Nature.

[36]  R. Benz,et al.  The Preprotein Translocation Channel of the Outer Membrane of Mitochondria , 1998, Cell.

[37]  A. Messina,et al.  Novel aspects of the electrophysiology of mitochondrial porin. , 1998, Biochemical and biophysical research communications.

[38]  C. Clayton,et al.  Conservation of mitochondrial targeting sequence function in mitochondrial and hydrogenosomal proteins from the early-branching eukaryotes Crithidia, Trypanosoma and Trichomonas. , 1997, European journal of cell biology.

[39]  G. R. Smith,et al.  A novel method for structure-based prediction of ion channel conductance properties. , 1997, Biophysical journal.

[40]  A. Schneider,et al.  In vitro import of proteins into mitochondria of Trypanosoma brucei and Leishmania tarentolae. , 1996, Journal of cell science.

[41]  J B Patlak,et al.  Measuring kinetics of complex single ion channel data using mean-variance histograms. , 1993, Biophysical journal.

[42]  A. Mauro,et al.  Voltage gating of conductance in lipid bilayers induced by porin from outer membrane of Neisseria gonorrhoeae. , 1988, Proceedings of the National Academy of Sciences of the United States of America.

[43]  K. Magleby,et al.  Sampling, log binning, fitting, and plotting durations of open and shut intervals from single channels and the effects of noise , 1987, Pflügers Archiv - European Journal of Physiology.

[44]  F. Pattus,et al.  The selectivity filter of voltage‐dependent channels formed by phosphoporin (PhoE protein) from E. coli. , 1986, The EMBO journal.

[45]  J. Rosenbusch,et al.  Porin channel triplets merge into single outlets in Escherichia coli outer membranes , 1985, Nature.

[46]  A. Glück,et al.  Characterisation of YtfM, a second member of the Omp85 family in Escherichia coli , 2007, Biological chemistry.

[47]  A. Delcour Structure and function of pore-forming beta-barrels from bacteria. , 2002, Journal of molecular microbiology and biotechnology.

[48]  J. Ruppersberg Ion Channels in Excitable Membranes , 1996 .