Structural basis for late maturation steps of the human mitoribosomal large subunit

Area of Science:

• Molecular Biology
• Cell Biology
• Structural Biology

Background:

• Mitochondrial ribosomes (mitoribosomes) produce proteins vital for cellular energy via oxidative phosphorylation.
• Understanding mitoribosome biogenesis is key to cellular energy supply, but pathways remain unclear.

Purpose of the Study:

• To elucidate the late stages of mitochondrial large subunit (mt-LSU) biogenesis.
• To investigate the roles of assembly factors, particularly GTPBP5, in mitoribosome assembly.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine structures of human mitoribosomes.
• Structures were analyzed from cell lines with depleted or overexpressed GTPBP5.

Main Results:

• Cryo-EM structures revealed consecutive steps in mt-LSU biogenesis.
• Identified nine assembly factors coordinating 16S rRNA folding, methylation, and peptidyl transferase centre (PTC) completion.
• Showcased MTERF4's role in rRNA folding, MRM2 in methylation, and GTPBP5/NSUN4 in PTC formation.
• Discovered mtEF-Tu's novel involvement in mt-LSU assembly through interaction with GTPBP5.

Conclusions:

• Detailed molecular mechanisms for late-stage mt-LSU biogenesis are presented.
• The coordinated action of specific assembly factors is essential for functional mitoribosome formation.
• mtEF-Tu has a previously unrecognized role in mitochondrial ribosome assembly.