Molecular mechanisms of transport of proteins across the mitochondrial inner membrane

• Applicant: Dr. Dejana Mokranjac
• Subject Area: Biochemistry
• Term: from 2012 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 222379219

Mitochondria are cell organelles that host many of the essential cellular processes ranging from energy metabolism and production of many metabolites to regulation of apoptosis. Their dysfunction is associated with a number of human disorders, including neurodegenerative disorders, diabetes and various forms of cancer, in addition to many hereditary diseases directly caused by mutations in mitochondrial proteins. The structure and function of mitochondria strictly depend on import of approximately 1000 different proteins from the cytosol. More than half of these proteins are synthesized with cleavable, N-terminal extensions, termed presequences and use the TIM23 complex in the inner membrane for their translocation into mitochondria. Research in the recent years revealed an unexpected complexity of the TIM23 complex. Using the energy of membrane potential across the inner membrane and ATP in the matrix, the TIM23 complex mediates translocation of proteins across and their insertion into the mitochondrial inner membrane. How the 11 subunits of this complex cooperate to achieve these tasks is only poorly understood. We have established a number of assays that will allow us to combine biochemistry, cell biology and genetics with biophysics and structural biology in order in order to understand the molecular mechanisms of function of this remarkable molecular machine. In one approach, we will use recent developments in mass spectrometry and biophysics to analyze, in the native environment, the dynamic organization of the ATP-consuming part of the complex and its coupling with the translocation channel. In a complementary approach, we want to reconstitute the function of the TIM23 complex entirely from recombinant proteins, based on a system we recently developed to recombinantly express and purify the components of the translocation channel. We envisage that these experiments will allow us to dissect, with high precision, the individual steps of function of the TIM23 complex and help us understand how it converts the two energy sources into unidirectional transport of proteins across the mitochondrial inner membrane.

• DFG Programme: Research Grants