6r7l
Ribosome-bound SecYEG translocon in a nanodisc
Structural highlights
FunctionSECE_ECOLI Essential subunit of the protein translocation channel SecYEG. Clamps together the 2 halves of SecY. May contact the channel plug during translocation. Overexpression of some hybrid proteins has been thought to jam the protein secretion apparatus resulting in cell death; while this may be true it also results in FtsH-mediated degradation of SecY.[1] Publication Abstract from PubMedThe Sec translocon provides the lipid bilayer entry for ribosome-bound nascent chains and thus facilitates membrane protein biogenesis. Despite the appreciated role of the native environment in the translocon:ribosome assembly, structural information on the complex in the lipid membrane is scarce. Here, we present a cryo-electron microscopy-based structure of bacterial translocon SecYEG in lipid nanodiscs and elucidate an early intermediate state upon insertion of the FtsQ anchor domain. Insertion of the short nascent chain causes initial displacements within the lateral gate of the translocon, where alpha-helices 2b, 7, and 8 tilt within the membrane core to "unzip" the gate at the cytoplasmic side. Molecular dynamics simulations demonstrate that the conformational change is reversed in the absence of the ribosome, and suggest that the accessory alpha-helices of SecE subunit modulate the lateral gate conformation. Site-specific cross-linking validates that the FtsQ nascent chain passes the lateral gate upon insertion. The structure and the biochemical data suggest that the partially inserted nascent chain remains highly flexible until it acquires the transmembrane topology. Partially inserted nascent chain unzips the lateral gate of the Sec translocon.,Kater L, Frieg B, Berninghausen O, Gohlke H, Beckmann R, Kedrov A EMBO Rep. 2019 Aug 5:e48191. doi: 10.15252/embr.201948191. PMID:31379073[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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