Understanding mitochondrial protein import and membrane insertion. (360G-Wellcome-104632_Z_14_Z)

The emergence of mitochondria from the assimilation of bacterial endosymbionts was a critical event in the evolution of modern eukaryotes and complex multicellular life. This process involved the relocation of swathes of the progenitor genome to the host nucleus, necessitating the co-evolution of a mitochondrial protein import apparatus: the focus of this proposal. The machinery is composed of the TOM (Translocon of the Outer Membrane) complex interfacing a range of partners (Figure 1; reviewed (1)): SAM (Sorting and Assembly Machinery) for the delivery of beta-barrelled proteins into the outer membrane; MIA (Mitochondrial Inter-membrane Space Import and Assembly) and the TIM (Translocon of the Inner Membrane) complexes for translocation across and into the inner membrane. The TIM22 complex inserts proteins without N-terminal presequences (metabolite carriers) to the inner membrane, driven by the membrane potential; whilst the TIM23 complex directs precursor proteins (with presequences ) across or laterally into the membrane, also stimulated by membrane potential. Translocation through the membrane to the matrix requires the action of an associated PAM (Presequence translocase-Associated Motor), which utilises ATP to drive transport. They are all essential for cell viability. So far, their analysis has been restricted to low-resolution methods and they are not well understood. I aim to elucidate the mechanisms underlying mitochondrial protein import and insertion through a comprehensive analysis of the TOM and TIM complexes. My longer-term vision is understand their action in membrane protein complex assembly, membrane biogenesis, and how defects in this process may lead to a wide range of human health problems, including ageing. This in turn may help to develop tools for mitochondrial re-engineering, in the spirit of regenerative medicine and metabolic control.