Transient tertiary structure formation within the ribosome exit port

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• The ribosome exit tunnel is traditionally viewed as too narrow for co-translational protein folding.
• Protein folding is crucial for cellular function and is often assumed to occur post-translationally.

Purpose of the Study:

• To investigate the possibility of early protein folding initiation within the ribosome exit tunnel.
• To identify structural elements that can form during co-translational folding inside the ribosome.

Main Methods:

• Utilizing molecular simulations to model nascent chain behavior within the ribosome exit tunnel.
• Comparing simulation predictions with existing experimental data on ribosome-nascent chain complexes.

Main Results:

• Long-range contacts, essential for protein folding, can form within the last 20 Å of the ribosome exit tunnel.
• Significant native and non-native tertiary structures can form in the "exit port" without steric hindrance from the ribosome.
• Transient folded structures were observed, with peak stability at the tunnel's boundary.

Conclusions:

• Co-translational folding can initiate earlier than previously thought, within the ribosome exit tunnel.
• The ribosome exit tunnel provides a confined environment that facilitates early protein structural element formation.
• These findings offer a new framework for understanding co-translational folding and interpreting experimental data.