Fe-S clusters-binding proteins in mitoribosome

The human mitochondrial ribosome contains three [2Fe-2S] clusters whose assembly pathway, role, and implications for mitochondrial and metabolic diseases are unknown. Here, structure-function correlation studies show that the clusters play structural roles during mitoribosome assembly. To uncover the assembly pathway, we have examined the effect of silencing the expression of Fe-S cluster biosynthetic and delivery factors on mitoribosome stability. We have found that the mitoribosome receives its [2Fe-2S] clusters from the GLRX5-BOLA3. Additionally, the assembly of the small subunit depends on METTL17, recently reported to contain a [4Fe-4S] cluster, which we found to be inserted via ISCA1-NFU1. Consistently, fibroblasts from patients suffering from “multiple mitochondrial dysfunction” syndrome due to mutations in BOLA3 or NFU1 display previously unrecognized attenuation of mitochondrial protein synthesis that contributes to their cellular and pathophysiological phenotypes. Finally, we report that, in addition to their structural role, the mitoribosomal [2Fe-2S] clusters sense changes in the redox environment. In this way, the mitoribosome checks the availability and stability of mitochondrial Fe-S clusters to regulate organellar protein synthesis accordingly.