SecYEG: plug-and-play!

PhD ceremony: Mr. J.A. Lijcklama à Nijeholt, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: SecYEG: plug-and-play!

Promotor(s): prof. A.J.M. Driessen

Faculty: Mathematics and Natural Sciences

In bacteria, the outside world is separated from the interior by only one or a few membrane layers consisting of lipids. Proteins produced in the cell often need to be transported across or into these membranes. This process is facilitated by a specialized transport mechanism, where the membrane complex SecYEG plays a central role as a protein conducting channel. The motor protein SecA actively guides the secretory protein through this channel.

In his thesis Jelger Lycklama à Nijeholt has in particularly studied the opening mechanism of the SecYEG translocation channel. The channel has an hourglass shape, whereby the exit is blocked by a helical segment of SecY termed the plug. Among others, he assessed to what extent the plug has to move to vacate the central channel for proteins to pass. By fixing the plug at different locations and subsequently measuring protein translocation, it was concluded by Lycklama à Nijeholt that the plug only exhibits a minimal movement to make way for the translocating protein. To analyze the plug dynamics he used a fluorescence based approach which could be used to probe the environment of the plug. During protein translocation, the plug was solvated by water as expected from the predicted channel opening mechanism. Surprisingly, during protein insertion, where the protein laterally inserta in the membrane layer instead of being translocated through the channel, there was no change is solvation and thus no movement of the plug. This indicates that the plug recognizes the incoming protein and will move away if the protein has to pass, but stays at its central position when a membrane protein enters the lipid bilayer.