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      X-ray structure of a protein-conducting channel.

      Nature

      genetics, metabolism, Crystallography, X-Ray, Escherichia coli Proteins, chemistry, ultrastructure, Macromolecular Substances, Methanococcus, Models, Molecular, Protein Binding, Protein Structure, Quaternary, Protein Structure, Secondary, Protein Subunits, Protein Transport, Static Electricity, Suppression, Genetic, Archaeal Proteins

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          Abstract

          A conserved heterotrimeric membrane protein complex, the Sec61 or SecY complex, forms a protein-conducting channel, allowing polypeptides to be transferred across or integrated into membranes. We report the crystal structure of the complex from Methanococcus jannaschii at a resolution of 3.2 A. The structure suggests that one copy of the heterotrimer serves as a functional translocation channel. The alpha-subunit has two linked halves, transmembrane segments 1-5 and 6-10, clamped together by the gamma-subunit. A cytoplasmic funnel leading into the channel is plugged by a short helix. Plug displacement can open the channel into an 'hourglass' with a ring of hydrophobic residues at its constriction. This ring may form a seal around the translocating polypeptide, hindering the permeation of other molecules. The structure also suggests mechanisms for signal-sequence recognition and for the lateral exit of transmembrane segments of nascent membrane proteins into lipid, and indicates binding sites for partners that provide the driving force for translocation.

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          Journal
          14661030
          10.1038/nature02218

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