Wednesday, May 4, 2011

Ribosome-SecYEG visualized in a membrane environment

A sub-nanometer cryo-EM reconstruction of the ribosome-SecYEG complex has been reported in the latest issue of Nature Structural & Molecular Biology. MDFF was employed to interpret the cryo-EM data at atomic level. The work is a collaboration between the Schulten (University of Illinois at Urbana-Champaign, USA) and Beckmann (University of Munich, Germany) groups.

Cryo-EM structure of the ribosome-SecYE complex in the membrane environment.
Jens Frauenfeld, James Gumbart, Eli O. van der Sluis, Soledad Funes, Marco Gartmann, Birgitta Beatrix, Thorsten Mielke, Otto Berninghausen, Thomas Becker, Klaus Schulten, and Roland Beckmann. Nat. Struct. Mol. Biol., 18, 614-621, 2011.

The ubiquitous SecY–Sec61 complex translocates nascent secretory proteins across cellular membranes and integrates membrane proteins into lipid bilayers. Several structures of mostly detergent-solubilized Sec complexes have been reported. Here we present a single-particle cryo-EM structure of the SecYEG complex in a membrane environment, bound to a translating ribosome, at subnanometer resolution. Using the SecYEG complex reconstituted in a so-called Nanodisc, we could trace the nascent polypeptide chain from the peptidyltransferase center into the membrane. The reconstruction allowed for the identification of ribosome–lipid interactions. The rRNA helix 59 (H59) directly contacts the lipid surface and appears to modulate the membrane in immediate vicinity to the proposed lateral gate of the protein-conducting channel (PCC). On the basis of our map and molecular dynamics simulations, we present a model of a signal anchor–gated PCC in the membrane.