GTPBP8 is essential for mitoribosome formation in human mitochondria

Mitochondrial gene expression relies on mitoribosomes to translate mitochondrial mRNAs. The biogenesis of mitoribosomes is an intricate process involving multiple assembly factors. Among these factors, GTP-binding proteins (GTPBPs) play crucial roles. In bacterial systems, numerous GTPBPs are required for ribosome subunit maturation, with EngB being a GTPBP involved in the ribosomal large subunit assembly. In this study, we focused on exploring the function of GTPBP8, the human homolog of EngB. We found that ablation of GTPBP8 leads to the inhibition of mitochondrial translation, resulting in significant impairment of oxidative phosphorylation. Structural analysis of mitoribosomes from GTPBP8 knock-out cells showed the accumulation of mitoribosomal large subunit assembly intermediates that are incapable of forming functional monosomes. Furthermore, fPAR-CLIP analysis revealed that GTPBP8 is an RNA-binding protein that interacts specifically with the mitochondrial ribosome large subunit16S rRNA. Our study highlights the crucial role of GTPBP8 as a component of the mitochondrial gene expression machinery involved in mitochondrial large subunit maturation. Overall design: We performed Flag-GTPBP8 and V5-AUH fPAR-CLIP to assess protein occupancy on RNA targets in doxacycline incudcible HEK293 cells from whole cell lysates