Three-dimensional structures of translating ribosomes by Cryo-EM

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Ribosomes are essential molecular machines responsible for protein synthesis.
• Understanding ribosome structure and function is crucial for deciphering cellular processes.
• Stalled ribosomes provide insights into translation regulation and protein folding.

Purpose of the Study:

• To investigate the structural consequences of translation stalling in E. coli ribosomes.
• To identify structural differences between stalled and non-translating ribosomes.
• To explore the potential role of the ribosomal tunnel in nascent polypeptide chain folding.

Main Methods:

• Cryo-electron microscopy (Cryo-EM) was employed to capture high-resolution structures.
• Advanced image reconstruction techniques were utilized to generate 3D maps.
• Comparative analysis of electron density maps from stalled and non-translating ribosomes.

Main Results:

• Three-dimensional maps of E. coli ribosomes stalled during the translation of three proteins were obtained at 13-16 Å resolution.
• Specific structural differences were identified in stalled ribosomes compared to non-translating ribosomes.
• tRNAs, mRNA, and additional material were observed in stalled ribosome complexes.
• The tunnel within the large ribosomal subunit was found to be partially occluded in all stalled structures.

Conclusions:

• Nascent polypeptide chains may occupy an expanded ribosomal tunnel, potentially adopting rudimentary globular conformations.
• The partial occlusion of the ribosomal tunnel suggests a role in early protein folding events.
• These findings highlight the dynamic nature of the ribosome and its interaction with nascent proteins during translation.