Science at the Shine Dome 2010

New Fellows Seminar

Wednesday 5 May

Professor Trevor Lithgow FAA
Department of Biochemistry and Molecular Biology, Monash University

Trevor Lithgow was awarded his PhD from La Trobe University in 1992 and completed postdoctoral work at the University of Basel. In 2008 he was awarded an ARC Federation Fellowship to move to the new Biosciences Precinct at Monash University. He has made major contributions in microbial cell biology and genetics. He is one of Australia’s leading yeast geneticists, with a history of using yeast as a model to understand complex aspects of cell biology. Trevor’s work on mitochondrial biogenesis, particularly the protein import pathway into mitochondria, places him amongst the top molecular microbiologists in the world. His use of bioinformatics has enabled work on protein transport, particularly the ‘molecular machines’ that drive it, to be characterised in bacteria, Giardia, trypanosomes and other microbes. He has taught biochemistry, microbial cell biology and genetics to thousands of students at three leading universities.

Rise of the machines: The evolution of protein transportation machines in mitochondria

The human body is made up of billions of cells. The differences in these cell types are evident: nerve cells, muscle cells, blood cells and so on, but so too are some of the fundamental similarities. All human cells are divided off in compartments. Each of these compartments provides a distinct function to the cell. For example, the nucleus of our cells houses chromosomes carrying the genes that you inherit from your parents and pass to your children. Another example is mitochondria, famous as the ‘powerhouses’ of our cells. In fact, our cells – and all eukaryotic cells – are chimeras composed of parts from two different, simpler organisms. Numerous studies have shown that the first eukaryotes (the ancestors of our cells) cultivated species of bacteria in their cytoplasm which were converted, over time, to mitochondria.

There are molecular machines in the outer and inner membranes of mitochondria, which serve to transport proteins (these proteins are encoded in the genes in the cell’s nucleus) to the inside of mitochondria – that is, they assist mitochondria to ‘import’ proteins. This matters because our mitochondria can only make 13 of the 1500 proteins they need and have to import the rest. But the ancestral bacterium would not have imported proteins; no bacteria we know of can. So where did these protein-importing molecular machines come from? We have spent the past few years testing the hypothesis that protein import machines evolved from simple, component parts that were present in the ancestral bacterium. These components combined together in a new way so that they could drive a new function, in keeping with the general principles of evolution. This hypothesis makes the prediction that modern-day bacteria, those related to the group from which mitochondria arose, might have the component parts of protein import ‘molecular machines’ even now, but functioning in processes other than protein import. Very recent discoveries show that this is indeed the case.