Mitochondria are often referred to as the powerhouses of our cells, because they generate chemical energy similar to that obtained from a battery. Whether it's a brain, muscle or plant cell, nano-sized gateways control the activity of the mitochondrial battery, by carefully allowing certain proteins and other molecules to enter into our mitochondria. Some of these proteins are large and complex molecules, yet they are essentially "spirited" into from the cytoplasm into the mitochondria, while the mitochondrial membrane remains water-tight and intact. How this happens has confounded science for decades.
Monash researchers, working with colleagues in Japan, have shown how molecules manage this sub-cellular voyage and have visualized the process with new, atomic-resolution imaging -- in real time. The discovery reveals what has been an essential mystery in biology and is published on 25 September in the journal, Science.
According to the lead researcher, Professor Trevor Lithgow, from the newly launched Biomedicine Discovery Institute (BDI) at Monash University in Melbourne, Australia, the discovery means that scientists can now use the technology to determine how any molecule passes through any membrane. "How large molecules like proteins get in and out of membranes has long been a mystery. We have shown that this technology can be applied to solve the atomic scale details for all sorts of fundamental pathways going on in cells, opening the way to direct applications for medical research" he said.
Professor Lithgow and his team used a novel technology that enables the systematic expansion of the genetic codes of living organisms to include unnatural amino acids beyond the common twenty. The technology had been used in a handful of labs outside of Australia. Professor Lithgow and lead researcher Dr. Takuya Shiota from the BDI focused on the TOM protein complex, a large, complicated set of molecules embedded in the mitochondrial membrane in ways that have long confounded researchers. According to Professor Lithgow TOM 40 has resisted all attempts, using x-ray crystallography and other standard techniques in structural biology to unlock its transport secrets.
The Lithgow lab, working with colleagues from Nagoya, Kyoto and Tokyo, ramped up scale of the technology making literally hundreds of re-coded TOM 40 complexes, each one with a novel additional 21st amino acid. What they ended up with was a Rubik's Cube of three dimensional data, which in the end had a unique solution that explained the structure of the TOM 40 protein complex and precisely how it operates as the gateway for entry into mitochondria.
Having shown the technology works -- Professor Lithgow believes other labs working on diverse processes in human cell biology will mimic these experiments to determine how their chosen nanomachines operate. This includes processes from DNA damage and repair, to regulation events in metabolic disorders and cancer. "This new technology has revealed what has been a major unknown in biology, and other cellular mysteries are now ripe for the picking" he said.
The research is the culmination of more than 15 years work by Professor Lithgow, from the newly launched Biomedicine Discovery Institute (BDI) at Monash University. He started working on the process of how proteins and other molecules enter into mitochondria as a post-doctoral researcher for the Human Frontiers Science Program in Basel, and after returning to Australia continued to seek TOM 40's secret. "With this discovery I'll focus for a couple more years to transfer this technology across to other labs in Australia, but I will then bow out: we will have by then answered all the questions that have driven me since my time in Switzerland," he said.
The research paper is the first from Monash's new BDI which announces its presence with research published in Science. According to Professor John Carroll, Director of the BDI, the research is a great example of the interdisciplinary approach that will be the hallmark of the Institute. "We bring scientists from across all the biomedical disciplines together with mathematicians, chemists and others to make important discoveries that provide critical new information about how our bodies function. The international effort needed to unlock this problem is a great example of the global nature of modern biomedical research. It is essential to work with the best and most talented scientists irrespective of where they are based in the world," he said.