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The molecular choreography of the Sec translocation system

From in vivo to in vitro
PhD ceremony:Mr A.B. (Anne-Bart) Seinen
When:February 18, 2019
Supervisors:prof. dr. A.J.M. (Arnold J M) Driessen, prof. dr. A.M. (Antoine) van Oijen
Where:Academy building RUG
Faculty:Science and Engineering

The cell is the basic structural part of all living matter on Earth. The shape and size of a single cell vary tremendously, however, a common feature shared by all cells is that the interior is separated from the environment by a membrane. To support life, a cell needs to take up nutrients from its environment and secrete products. However, most nutrients need specialized channels in the membrane to pass this barrier. These specialized channels are protein (complexes) embedded in the membrane, which are inserted into this membrane by a highly conserved protein secretion complex termed Sec61 for Eukaryotes and SecYEG for Bacteria. The proteins constituting the bacterial SecYEG secretion pathway are intensively studied, albeit often in bulk causing ensemble averaging and/or indirectly. In this project, super-resolution microscopy was used to visualize for the first time the dynamical organization of the different protein components of the secretion complex at the single-molecule in living Escherichia coli cells. With this technique, it was for the first time shown that the protein components constituting the channel itself and accessory proteins are highly dynamic. Evidence was found that a large protein complex, termed the holotranslocon, forms on-demand to carry out its function of inserting proteins into or translocating polypeptides across the membrane. The study also focused on the motor component of the systems, SecA, which provides the force to drive a protein through the SecYEG channel. It was found that SecA is dimeric and predominantly bound to the cytoplasmic membrane.