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In mitochondrial disease respiratory complex III2 assembles complex I via toxic intermediate

Ayala-Hernandez, M. G.; Torales, A. B.; Tan, H. C.; Montgomery, C. B.; Padavannil, A.; Cortopassi, G.; Letts, J. A.

2025-06-18 biochemistry
10.1101/2025.06.17.660237 bioRxiv
Show abstract

Mutations in mitochondrial complex I can cause severe metabolic disease. Although no treatments are available for complex I deficiencies, chronic hypoxia improves lifespan and function in a mouse model of the severe mitochondrial disease Leigh syndrome caused by mutation of complex I subunit NDUFS4. To understand the molecular mechanism of NDUFS4 mutant pathophysiology and hypoxia rescue, we investigated the structure of complex I in respiratory supercomplexes isolated from NDUFS4 mutant mice. We identified complex I assembly intermediates bound to complex III2, proving the cooperative assembly model. Further, an accumulated complex I intermediate is structurally consistent with pathological oxygen-dependent reverse electron transfer, revealing unanticipated pathophysiology and hypoxia rescue mechanisms. Thus, the build-up of toxic intermediates and not simply decreases in complex I levels underlie mitochondrial disease.

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