Pseudouridine synthase PUS1 and initiation factor mtIF2 are human mitoribosomal small subunit assembly factors

Area of Science:

• Molecular Biology
• Cell Biology
• Structural Biology

Background:

• Mitochondrial ribosomes (mitoribosomes) are essential for producing oxidative phosphorylation machinery subunits.
• Mitoribosome assembly defects are linked to severe human diseases.
• Understanding mitoribosome biogenesis is crucial for both health and disease research.

Purpose of the Study:

• To structurally characterize intermediate assembly states of the human mitoribosomal small subunit (mtSSU).
• To elucidate the final maturation steps of the mtSSU, including the platform, decoding center, and 12S rRNA 3'-end.
• To identify key assembly factors involved in these late-stage maturation processes.

Main Methods:

• Isolation and structural analysis of twelve distinct mtSSU assembly intermediates from human cells.
• Detailed structural characterization of rRNA folding and mitoribosomal protein integration.
• Identification of specific assembly factors through analysis of the isolated intermediates.

Main Results:

• Detailed structural insights into the final maturation stages of the mtSSU platform, decoding center, and 12S rRNA 3'-end.
• Identification of pseudouridine synthase PUS1 and initiation factor mtIF2 as crucial assembly factors in mtSSU maturation.
• Demonstration of coordinated actions of assembly factors ensuring precise rRNA folding and protein integration.

Conclusions:

• The study reveals the modular nature of mtSSU biogenesis and the intricate coordination of assembly factors.
• New roles for PUS1 and mtIF2 in mitoribosome assembly are identified, expanding their known functions.
• Late-stage mtSSU assembly is directly linked to the acquisition of translational competence, impacting mitochondrial function.