Interconnected assembly factors regulate the biogenesis of mitoribosomal large subunit. (12th February 2021)

• Record Type: Journal Article
• Authors: Tobiasson, Victor; Gahura, Ondřej; Aibara, Shintaro; Baradaran, Rozbeh; Zíková, Alena; Amunts, Alexey
• Is Part Of: EMBO journal. Volume 40:Number 6(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-02-12
• Subjects: assembly -- mitochondria -- mitoribosome -- translation -- trypanosoma; Molecular biology -- Periodicals; 572.805
• DOI: 10.15252/embj.2020106292
• Languages: English
• ISSNs: 0261-4189

Abstract

Abstract: Mitoribosomes consist of ribosomal RNA and protein components, coordinated assembly of which is critical for function. We used mitoribosomes from Trypanosoma brucei with reduced RNA and increased protein mass to provide insights into the biogenesis of the mitoribosomal large subunit. Structural characterization of a stable assembly intermediate revealed 22 assembly factors, some of which have orthologues/counterparts/homologues in mammalian genomes. These assembly factors form a protein network that spans a distance of 180 Å, shielding the ribosomal RNA surface. The central protuberance and L7/L12 stalk are not assembled entirely and require removal of assembly factors and remodeling of the mitoribosomal proteins to become functional. The conserved proteins GTPBP7 and mt‐EngA are bound together at the subunit interface in proximity to the peptidyl transferase center. A mitochondrial acyl‐carrier protein plays a role in docking the L1 stalk, which needs to be repositioned during maturation. Additional enzymatically deactivated factors scaffold the assembly while the exit tunnel is blocked. Together, this extensive network of accessory factors stabilizes the immature sites and connects the functionally important regions of the mitoribosomal large subunit. SYNOPSIS: The formation of the mitoribosome is an intricate process involving multiple protein factors that work in coordination. Here, structural characterisation of a T. brucei mitoribosomal large subunit assembly intermediate reveals the specific roles of an extensive assembly factor network. Cryo‐EM of a mitoribosomal large subunit assembly intermediate reveals 22 associated assembly factors. The 180 Å‐spanning network shields the ribosomal RNA surface and connects functionally important regions. The central protuberance and the L7/L12 stalk are pre‐assembled in a non‐functional form Conserved proteins GTPBP7 and mt‐EngA bind together at the subunit interface A mitochondrial acyl‐carrier protein plays a role in docking the L1 stalk. Assembly factors such as MRM and RPUSD4 represent catalytically‐inactivated enzymes serving as structural mediators. Abstract : Cryo‐EM structures of a Trypanosoma brucei mitoribosomal large subunit assembly intermediate reveals the specific roles of an extensive assembly factor network.