The SecYEG complex forms a protein-conducting channel in the inner membrane of Escherichia coli to support the translocation of secretory proteins in their unfolded state. The SecY channel is closed at the periplasmic face of the membrane by a small re-entrance loop that connects transmembrane segment 1 with 2b. This helical domain 2a is termed the plug domain. By the introduction of pairs of cysteines and crosslinkers, the plug domain was immobilized inside the channel and connected to transmembrane segment 10. Translocation was inhibited to various degrees depending on the position and crosslinker spacer length. With one of the crosslinked mutants translocation occurred unrestricted. Biochemical characterization of this mutant as well as molecular dynamics simulations suggest that only a limited movement of the plug domain suffices for translocation.

The film presents 0.5 microseconds simulations of the SecYEGA complex embedded in a POPC membrane in water in the case of a BMH bond between cysteines 67C and 394C.

The yellow beads represent the cysteine residues while the residues forming the hydrophobic ring in the middle of the channel are depicted by red beads.

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Lycklama a Nijeholt, Bulacu et al., J. Biol. Chem., 285 (31) 23747 (2010)
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