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. In the absence of GTPBP8, numerous mitoribosomal proteins from both subunits become destabilized, indicating GTPBP8's involvement in synchronized subunit assembly. Furthermore, 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. Our study highlights the crucial role of GTPBP8 as a component of the mitochondrial gene expression machinery involved in mitoribosome biogenesis. Overall design: The mitochondrial translation was investigated by mitochondrial ribosome profiling (mitoRiboSeq) in two HEK293 cell lines: HEK293 wildtype, GTPBP8 knockout 1