Molecular mechanisms of cooperation of the TOM and TIM23 complexes during translocation of proteins into mitochondria

• Applicant: Dr. Dejana Mokranjac
• Subject Area: Biochemistry
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 450889947

Biogenesis of mitochondria strictly depends on import of over thousand different proteins synthesized on cytosolic ribosomes as precursor proteins with specific mitochondrial targeting signals. Recognition, translocation and intamitochondrial sorting of precursor proteins is mediated by a number of different mitochondrial protein translocases, complex molecular machines present in all mitochondrial subcompartments. The majority of precursor proteins are targeted to mitochondria with N-terminal, positively charged presequences and are translocated across the outer and inner membranes by the TOM and TIM23 complexes, respectively. How mitochondrial protein translocases cooperate with each other in order to transport precursor proteins to the final place of their function within the organelle is only poorly understood. Here, we will combine biochemistry with cell biology, genetics and structural biology to understand, on the molecular level, how presequence-containing precursor proteins are translocated across two mitochondrial membranes in a coordinated fashion. In one approach, we will dissect how the dynamic interactions of the two domains of Tim50 in the intermembrane space enable coordinated transfer of precursor proteins between the translocation channels in the outer and inner membranes. To reach this goal, in addition to a battery of well-established methods, we will make use of our unexpected observation that the function of Tim50 can be reconstituted in vivo from its domains expressed in trans. In the second approach, we will structurally and functionally characterize the TOM-TIM23 supercomplex. For this, particularly useful will be the tool we recently developed to covalently couple the TOM and TIM23 complexes in vivo. We expect to obtain a molecular understanding of how protein translocases present in two different membranes cooperate with each other and thus gain an important insight into molecular mechanisms of biogenesis of mitochondria.

• DFG Programme: Research Grants