Question

When is GTP hydrolyzed between SRP and SRP-R?

Answer 1

GTP hydrolysis occurs upon the binding of the ribosome-SRP complex to the SRP receptor on the RER membrane, which is a critical step for the continuation of protein translation into the RER lumen.

Step-by-step explanation:

Hydrolysis of GTP during Protein Targeting to the RER

The interaction between the Signal Recognition Particle (SRP) and the SRP Receptor (SRP-R) involves the hydrolysis of GTP. This process unfolds as follows:

1. An SRP binds to the signal peptide of a nascent polypeptide as it emerges from the ribosome.
2. The ribosome-SRP complex then halts translation and targets the RER membrane by binding to a specific SRP receptor (SRP-R).
3. Upon binding to the SRP-R, GTP is hydrolyzed. This event is crucial for the release of the SRP and the continuation of protein translation into the lumen of the RER.

The hydrolysis of GTP is a pivotal step that ensures the proper targeting and insertion of the growing polypeptide into the RER for subsequent folding and modification.