Biogenesis of Respiratory Chain Complex I and Analysis of Assembly Defects in Patients with Mitochondrial Disease

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Complex I of the mitochondrial respiratory chain is a large assembly of protein subunits that is involved in the main production of cellular energy. Complex I is found in intracellular compartments termed mitochondria. The predicament for Complex I is that in order for it to be built, it requires 38 different proteins that are made in one place in the cell to be imported into mitochondria and then somehow joined together with the 7 other subunits that are made by mitochondria. This is clearly a complicated procedure and we have little information on how its assembly is achieved. We do know however that mistakes in the assembly of Complex I do happen. In Australia, about 50 children born each year have inherited disorders of mitochondrial energy generation. The most severe disorders cause infant death, while others present later causing a range of degenerative diseases, particularly affecting brain, muscle and heart. The most common defect in these patients is a loss in the activity of Complex I. Interestingly it seems that in most cases, the defect is not due to a mutation in one or more of the Complex I subunits and so we believe that such defects arise form accessory proteins that are involved in the construction of Complex I. The aim of this proposal is to investigate how Complex I is assembled and to identify and characterise accessory proteins. We will also analyse assembly defects by studying skin fibroblasts from patients. This work will aid in our understanding of not only how protein complexes are built, but how defects in their assembly can cause disease. This will not only be informative to families of affected individuals but may aid in future diagnosis and prevention of mitochondrial disease.