Abstract
The MICOS complex, essential for cristae organization, comprises MIC10 and MIC60 subcomplexes, with MIC13 as a crucial subunit. MIC13 mutations cause severe mitochondrial hepato-encephalopathy, cristae defects, and MIC10-subcomplex loss. We demonstrate that depletion of the mitochondrial protease YME1L in MIC13 KO stabilizes MIC10-subcomplex, restoring MIC60-MIC10 interaction and crista junction (CJ) defects, indicating MIC13 is crucial for MIC10-subcomplex stabilization rather than MIC60-MIC10 bridging. We identified stomatin-like protein 2 (SLP2) as a key MIC13 interaction partner, essential for cristae morphology and CJ formation. SLP2 serves as an interaction hub for MICOS subunits and stabilizes MIC26 by protecting it from YME1L-mediated degradation. Deleting both SLP2 and MIC13 impairs MIC60-subcomplex assembly and its nanoscale organization. Restoring the MIC10-subcomplex in MIC13-SLP2 double KO cells through YME1L depletion reinstates MIC60-subcomplex assembly and cristae morphology. Overall, we propose SLP2 and the MIC10-subcomplex act as a proteolytically controlled 'seeder' complex, facilitating MICOS-MIB complex assembly and maintaining mitochondrial integrity.