X-ray structure of a protein-conducting channel

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 Å. The structure suggests that one copy of the heterotrimer serves as a functional translocation channel. The α-subunit has two linked halves, transmembrane segments 1–5 and 6–10, clamped together by the γ-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.

Additional Information

© 2004 Nature Publishing Group. Received 14 October; accepted 19 November 2003; Published online 3 December 2003. We thank R. MacKinnon for advice and suggestions of reagents; F. Duong for clones; J. Walker for C43 cells; C. Vonrhein, T. Terwilliger and K. Cowtan for help with software; M. Becker, L. Berman and S. LaMarra for support at beamline X25 at the National Synchrotron Light Source (Brookhaven National Laboratory, supported by the US Department of Energy, Division of Materials Sciences and Division of Chemical Sciences); A. Joachimiak, S. Ginell and R. Alkire for help at beamline 19ID at the Advanced Photon Source (supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences); and C. Ogata and M. Capel for help at beamline 8BM at the Advanced Photon Source (Northeastern Collaborative Access Team supported by an award from the National Center for Research Resources at the National Institutes of Health). We thank C. Akey, V. Ramakrishnan and particularly K. Matlack for critical reading of the manuscript. This work was supported by a fellowship from the Damon Runyon Cancer Research Foundation to W.M.C., and by fellowships from the Human Frontier Science Program Organization to I.C. and Y.M. E.H. was supported by grants from the Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie. T.A.R and S.C.H. are Howard Hughes Medical Institute Investigators.

Attached Files

Supplemental Material - nature02218-s1.rtf

Supplemental Material - nature02218-s2.jpg

Supplemental Material - nature02218-s3.jpg

Supplemental Material - nature02218-s4.jpg

Supplemental Material - nature02218-s5.jpg

Supplemental Material - nature02218-s6.jpg

Supplemental Material - nature02218-s7.rtf

Supplemental Material - nature02218-s8.rtf

Supplemental Material - nature02218-s9.rtf

Files

Additional details