Professor Trevor Lithgow

ARC Federation Fellow

Tel:      +61-3-9902 9217

Fax:     +61-3-9905 3726

Office:  Room 252, Level 2, Building 76 (STRIP 2)

Email:   trevor.lithgow@med.monash.edu.au

Our lab works on protein targeting; how proteins are sent to their correct sub-cellular location. This fundamental process is at the heart of how cells build their intracellular membranes, and how pathogenic microbes target toxic proteins to their hosts. Ten to twenty per cent of the proteins expressed in a given eukaryote cell are targeted to mitochondria, as are many effector proteins made by pathogenic bacteria.

Work in my laboratory falls into two broad themes: (i) the evolution of protein transport machines and (ii) the mechanism by which protein transporters function.  We are particularly interested in protein transport machines found in bacteria and in mitochondria; the two are related through evolution and we therefore study both.

We are part of the Molecular Biology of Host-pathogens Interactions Unit.   Several projects are underway in the lab to understand how proteins are targeted by microbial pathogens in order to pervert host cell biology.

Scholarship support is available to new PhD students. PhD postgraduate scholarships with an annual stipend of $20,007 (tax-free) are available for Australian citizens or permanent residents with a H1 Honours degree. We have positions for international students: applicants are advised to check the Graduate studies web pages for information on entry requirements, tuition fee, and scholarships prior to application.

Trevor's Favourite Links can be found here.

Evolution of Protein Transport Machines

The intracellular bacterium that gave rise to mitochondria has contributed much more than a ready source of ATP to the evolution of eukaryote cells. Our work shows that this organism played an active role in the evolution of new protein transport pathways that were essential to the development of the first eukaryotes.

Figure 1. Protein targeting to mitochondria across the board.  The mitochondrial protein import pathway has been characterized in detail in the yeast Saccharomyces cerevisiae. Analysis using hidden Markov models has uncovered that, while the basic components of the pathway are conserved across the board, fascinating differences exist in organisms like Trypanosoma brucei, Giardia inestinalis, Encephalizoon cuniculi and even other yeasts such as Saccharomyces castellii. We have established assays, in collaboration with experts around the world, to study protein transport in these organisms.

Link to the above article published in Science:

Mechanisms of Protein Transport and Assembly

Many of the mitochondrial protein transport systems share ancestry with biomedically important protein transporters in bacteria. Much of our current research aims at characterizing the function of protein transport machines in mitochondria and bacteria - using knowledge of the mitochondrial system and expertise in genetics, biochemistry and cell biology. We are working to understand how cell's regulate the assembly of mitochondrial membranes, how bacterial pathogens assemble protein transport machines in their outer membranes, and how these function to target "effector" proteins into human cells.

Figure 2. Targeting and assembly of proteins into outer membranes.  Projects in the lab aim at understanding how the SAM complex assembles proteins, like the TOM complex, in the mitochondrial outer membrane. In addition, we are working to understand how the BAM complex ("Omp85") assembles machines, like Type 5 secretion systems, in bacterial outer membranes.

New Projects

Honours and postgraduate projects employ a broad range of techniques in molecular biology, genetics, computer science and cell biology. New projects on offer include:

• Characterization of the targeting and assembly of lipids and proteins into the outer membrane and capsule of Klebsiella pneumoniae. This project is in collaboration with Professor Dick Strugnell and Dr. Michelle Gee (University of Melbourne). A combination of bioinformatics, mass spectrometry, atomic force microscopy and biochemical assays will be used for identification and characterization of the transporters responsible for assembly of the outer membrane and capsule.
  
  
• Defining step-by-step how integral membrane proteins are assembled into the mitochondrial outer membrane. This project will make use of yeast genetics and biochemical assays. Good evidence suggests a conserved mechanism is behind the assembly of tail-anchored proteins such as the Bcl-2 family and proteins with more complicated topologies such as beta-barrels. The structural and energetic demands of each process need to be defined.
  
  
• Using yeast genetics and systems biology approaches to screen for novel factors involved in the first steps of protein transport to mitochondria. Protein transport is subject to tight regulation in "time and space". Yeast provides a model to understand the regulatory mechanisms, which are at play in humans and other animals too.
  
  
• Characterization of the Type 5 secretion systems (T5SS) in EPEC (pathogenic Escherichia coli) and Salmonella spp. Many of these systems resemble "Omp85" type transport systems. This project is in collaboration with Professor Roy Robins-Browne and Dr. Vladimir Likić (University of Melbourne). A combination of bioinformatics, mass spectrometry and biochemical assays will be used for identification and characterization of the transporters.

Some Recent Publications from the Lithgow Lab

• Dolezal P, Likic V, Tachezy J, Lithgow T. (2006) Evolution of the molecular machines for protein import into mitochondria. Science 313: 314-8.
• Hulett JM, Walsh P, Lithgow T. (2007) Domain stealing by receptors in a protein transport complex. Mol. Biol. Evol. 24: 1909-11.
• Chan NC, Lithgow T. (2008) The peripheral membrane subunits of the SAM complex function codependently in mitochondrial outer membrane biogenesis. Mol. Biol. Cell 19: 126-36.
• Schneider A, Bursać D, Lithgow T. (2008) The direct route: a simplified pathway for protein import into the mitochondrion of trypanosomes. Trends Cell Biol. 18: 12-8.
• Gatsos X, Perry AJ, Anwari K, Dolezal P, Wolynec PP, Likić VA, Purcell AW, Buchanan SK, Lithgow T. (2008) Protein secretion and outer membrane assembly in alphaproteobacteria. FEMS Microbiol. Rev. 32, 995-1009
• Dagley MJ, Dolezal P, Likić VA, Smid O, Purcell AW, Buchanan SK, Tachezy J & Lithgow T. (2009) The protein import channel in the outer mitosomal membrane of Giardia intestinalis. Mol. Biol. Evol. 26: 1941-7 
• Clements A, Bursac D, Gatsos X, Perry AJ, Civciristov S, Celik N, Likic VA, Poggio S, Jacobs-Wagner C, Strugnell RA & Lithgow T. (2009) The reducible complexity of a mitochondrial molecular machine. Proc. Natl. Acad. Sci. 106: 15791-5
• Chacinska A, Koehler CM, Milenkovic D, Lithgow T, Pfanner N. (2009) Importing mitochondrial proteins: machineries and mechanisms. Cell 138: 628-44