Abstract
The trimeric Sec61/SecY complex is a protein-conducting channel (PCC) for secretory and membrane proteins. Although Sec complexes can form oligomers, it has been suggested that a single copy may serve as an active PCC. We determined subnanometer-resolution cryo-electron microscopy structures of eukaryotic ribosome-Sec61 complexes. In combination with biochemical data, we found that in both idle and active states, the Sec complex is not oligomeric and interacts mainly via two cytoplasmic loops with the universal ribosomal adaptor site. In the active state, the ribosomal tunnel and a central pore of the monomeric PCC were occupied by the nascent chain, contacting loop 6 of the Sec complex. This provides a structural basis for the activity of a solitary Sec complex in cotranslational protein translocation.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, Non-P.H.S.
MeSH terms
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Animals
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Binding Sites
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Cryoelectron Microscopy
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Dogs
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Image Processing, Computer-Assisted
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Membrane Proteins / chemistry*
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Membrane Proteins / metabolism*
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Membrane Proteins / ultrastructure
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Models, Molecular
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Protein Biosynthesis*
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Protein Conformation
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Protein Multimerization
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Protein Structure, Secondary
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Protein Transport*
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Proteins / chemistry
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Proteins / metabolism*
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Proteins / ultrastructure
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Ribosomes / metabolism*
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Ribosomes / ultrastructure
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Saccharomyces cerevisiae Proteins / chemistry*
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Saccharomyces cerevisiae Proteins / metabolism*
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Saccharomyces cerevisiae Proteins / ultrastructure
Substances
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Membrane Proteins
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Proteins
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SSH1 protein, S cerevisiae
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Saccharomyces cerevisiae Proteins
Associated data
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PDB/2WW9
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PDB/2WWA
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PDB/2WWB