Molecular and pathomechanistic roles of MIC13 in regulating cristae morphogenesis

• Applicant: Ruchika Anand, Ph.D.
• Subject Area: Biochemistry
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 445115201

Mitochondrial ultrastructure is uniquely characterized by invaginations of the inner membrane (IM) called cristae. The cristae are linked to the rest of the IM by peculiar, slot-like structures called crista junctions (CJs). CJs with diameter of 12-35 nm are suggested to provide a diffusion barrier that subdivides mitochondria into distinct subcompartments. CJs provide electric insulation between the cristae so that individual cristae can maintain different membrane potential. In our recent studies, we show that CJs and cristae undergo constant dynamic remodeling in a balanced and reversible manner that is dependent on MICOS complex (MIC13). The MICOS (mitochondrial contact site and cristae organizing system) complex is a large and highly conserved oligomeric complex that resides mainly at CJs and is required for formation and maintenance of CJs. It consists of seven subunits, MIC60, MIC25, MIC19, MIC13, MIC26, MIC27 and MIC10. Using complexome profiling, we have identified MIC13, MIC26 and MIC27 as novel subunits of the mammalian MICOS complex. MIC13 mutations in human cause a severe form of mitochondrial encephalopathy with liver dysfunction. We created knockout cells of MIC13 and observed a complete loss of CJs that is accompanied by degradation of subcomplex of MICOS containing MIC10, MIC26 and MIC27. This makes it difficult to analyze the individual role of MIC13 that is independent of the loss of MIC10, MIC26 and MIC27. Therefore, we planned to generate deletion variants of MIC13 across the length of protein and determine their ability to restore the MIC10, MIC26 and MIC27 and extent of rescue of the cristae defects. In our preliminary studies, we find that several deletion variants of MIC13 that could restore the levels of MIC10, MIC26 or MIC27, were not able to rescue the cristae defect completely. This provide us with a system to determine the molecular role of MIC13 that occur independent of MIC10, MIC26 or MIC27 in regulating cristae morphology. Therefore, this project is subdivided into three (a-c) feasible objectives, in (a) we plan to decipher the mechanistic role of MIC13 in CJ formation and MICOS integrity using the deletion variants. Further, (b) we aim to determine the pathomechanistic role of MIC13 (CJs) during cristae remodeling occurring during apoptosis. We found a novel interacting protein of MIC13 in the inner membrane. (c) Thus, we want to decipher the functional relationship between this factor and MIC13 (MICOS). With achieving these objectives, we will be able to answer fundamental questions about the molecular role of MIC13 in regulating cristae morphology and the pathomechanism of a disease linked to perturbation of cristae morphogenesis.

• DFG Programme: Research Grants