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Funes, S; Frauenfeld, J; Gumbart, J; van der Sluis, EO; Gartmann, M; Beatrix, B; Mielke, T; Berninghausen, O; Becker, T; Schulten, K; Beckmann, R (2011)

CRYO-EM STRUCTURE OF THE RIBOSOME-SECYE COMPLEX IN THE MEMBRANE ENVIRONMENT

NAT STRUCT MOL BIOL 18(5):614-U127
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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.