Structural Consequences of Deproteinating the 50S Ribosome

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Ribosomes are essential ribonucleoprotein particles responsible for protein synthesis.
• The 50S ribosomal subunit is a large component of the bacterial ribosome.
• Understanding ribosome assembly and disassembly is crucial for comprehending cellular processes.

Purpose of the Study:

• To determine the structures of E. coli 50S ribosomal core particles after high-salt wash using cryo-electron microscopy (cryo-EM).
• To investigate the in vitro disassembly process of 50S ribosomal subunits and its relationship to assembly pathways.
• To elucidate the role of ribosomal proteins (r-proteins) in stabilizing the native structure of 23S ribosomal RNA (rRNA).

Main Methods:

• Purification of E. coli 50S ribosomal subunits.
• High-salt wash to generate LiCl core particles.
• Cryo-electron microscopy (cryo-EM) for structural determination.
• Analysis of varying degrees of rRNA order and r-protein occupancy.

Main Results:

• Cryo-EM revealed a range of LiCl core particles with diverse rRNA structures and r-protein occupancy.
• Many particles resembled in vivo and in vitro assembly intermediates, indicating stable or metastable states.
• Observed a multi-pathway in vitro disassembly process, mirroring assembly, with protein extensions dissociating before globular domains.
• Demonstrated that r-proteins stabilize native rRNA structures and prevent non-native RNA folding upon dissociation.

Conclusions:

• Ribosomal proteins are critical for maintaining the native structure of ribosomal RNA.
• The in vitro disassembly of 50S subunits follows pathways similar but reverse to assembly.
• Protein-RNA interactions play a key role in the stability and structural integrity of ribosomes.