**6. Conclusions**

The central subunits of complex I harbor all bioenergetic core functions. Nevertheless, there is increasing evidence that mutations in accessory complex I subunits can have dramatic consequences and cause fatal disease. The pathophysiology of NDUFS4-linked Leigh syndrome is increasingly well understood. However, therapeutic approaches are still at an experimental stage. Loss of NDUFS4 affects complex I assembly and causes detrimental structural changes in assembled complex I. While animal models and mammalian cell lines are indispensable to study LS and possible therapeutic approaches, the yeast *Y. lipolytica* offers the advantage of straightforward gene manipulation and large-scale purification of complex I variants for biochemical, spectroscopic, and structural analysis of complex I and complex I variants.

**Author Contributions:** F.K., M.G. and V.Z. wrote the manuscript and prepared the figures. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Deutsche Forschungsgemeinschaft (DFG grant ZI552/4-2 to V.Z.).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

