X-ray structure of a protein-conducting channel.
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.
Van den Berg
Bert
B
Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA.
Clemons
William M
WM
Collinson
Ian
I
Modis
Yorgo
Y
Hartmann
Enno
E
Harrison
Stephen C
SC
Rapoport
Tom A
TA
D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000648:ultrastructure; D046911:Macromolecular Substances; D017017:Methanococcus / Q000737:chemistry*; D008958:Models, Molecular; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D021381:Protein Transport; D000069816:SEC Translocation Channels; D055672:Static Electricity; D013489:Suppression, Genetic
D019843:Archaeal Proteins; D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; D021122:Protein Subunits; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli