Dissecting the concordant and disparate roles of NDUFAF3 and NDUFAF4 in mitochondrial complex I biogenesis

Distinct sub-assemblies (modules) of mitochondrial complex I (CI) are assembled with the assistance of CI Assembly Factors (CIAFs) through mechanisms that are incompletely defined. Here, using genetic analyses in Drosophila, we report that when either of the CIAFs - NDUFAF3 or NDUFAF4 - is disrupted, biogenesis of the Q-, N-, and PP-b-modules of CI is impaired. This is due, at least in part, to the compromised integration of NDUFS3 and NDUFS5 into the Q-, and PP-b-modules, respectively, coupled with a destabilization of another CIAF, TIMMDC1, in assembly intermediates. Notably, forced expression of NDUFAF4 rescues the biogenesis defects in the Q-module and some aspects of the defects in the PP-b-module of CI when NDUFAF3 is disrupted. Altogether, our studies furnish new fundamental insights into the mechanism by which NDUFAF3 and NDUFAF4 regulate CI assembly and raises the possibility that certain point mutations in NDUFAF3 may be rescued by overexpression of NDUFAF4.

Automated summary

The study shows that NDUFAF3 and NDUFAF4 play crucial roles in the assembly of CI, disruption of which leads to defects in multiple modules of CI. Forced expression of NDUFAF4 can partially rescue some defects in CI, providing important insights for further research.