Final answer:
The signal peptidase cleaves the signal peptide from the protein once it has been threaded through the protein translocation channel into the lumen.
Step-by-step explanation:
After a protein has been threaded through the protein translocation channel into the lumen, the signal peptidase cleaves the signal peptide from the protein. The signal peptidase is an enzyme that catalyzes the co-translational hydrolysis of the signal peptide, which allows the protein to be released into the lumen. This cleavage step is important for the proper processing and function of the protein. The signal peptidase cleaves the signal peptide from the protein once it has been threaded through the protein translocation channel into the lumen.