The plug domain of the SecY protein stabilizes the closed state of the translocation channel and maintains a membrane seal.

Li W., Schulman S., Boyd D., Erlandson K., Beckwith J., and Rapoport T.A.
The plug domain of the SecY protein stabilizes the closed state of the translocation channel and maintains a membrane seal.
Mol Cell. 26(4):511-21. (2007, Cover Story) (Abstract)