Abstract
Ribosome biogenesis requires auxiliary factors to promote folding and assembly of ribosomal proteins and RNA. Particularly, maturation of the peptidyl transferase center (PTC) is mediated by conserved GTPases, but the molecular basis is poorly understood. Here, we define the mechanism of GTPase-driven maturation of the human mitochondrial large ribosomal subunit (mtLSU) using endogenous complex purification, in vitro reconstitution and cryo-EM. Structures of transient native mtLSU assembly intermediates that accumulate in GTPBP6-deficient cells reveal how the biogenesis factors GTPBP5, MTERF4 and NSUN4 facilitate PTC folding. Addition of recombinant GTPBP6 reconstitutes late mtLSU biogenesis in vitro and shows that GTPBP6 triggers a molecular switch and progression to a near-mature PTC state. Additionally, cryo-EM analysis of GTPBP6-treated mature mitochondrial ribosomes reveals the structural basis for the dual-role of GTPBP6 in ribosome biogenesis and recycling. Together, these results provide a framework for understanding step-wise PTC folding as a critical conserved quality control checkpoint.
Highlights
Ribosome biogenesis requires auxiliary factors to promote folding and assembly of ribosomal proteins and RNA
These results indicate that the GTPases act hierarchically and cooperate with other maturation factors during mitochondrial large ribosomal subunit (mtLSU) biogenesis
Two distinct mtLSU biogenesis intermediates accumulate in the absence of GTPBP6
Summary
Ribosome biogenesis requires auxiliary factors to promote folding and assembly of ribosomal proteins and RNA. The density could be unambiguously fit with the crystal structure of the complex of the RNA-binding protein MTERF4 and the methyltransferase NSUN415,16, with some adjustments (Supplementary Fig. 2a, b).
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