title: Disulfide bridge formation between SecY and a translocating polypeptide localizes the translocation pore to the center of SecY.
abstract: During their biosynthesis, many proteins pass through the membrane via a hydrophilic channel formed by the heterotrimeric Sec61/SecY complex. Whether this channel forms at the interface of multiple copies of Sec61/SecY or is intrinsic to a monomeric complex, as suggested by the recently solved X-ray structure of the Methanococcus jannaschii SecY complex, is a matter of contention. By introducing a single cysteine at various positions in Escherichia coli SecY and testing its ability to form a disulfide bond with a single cysteine in a translocating chain, we provide evidence that translocating polypeptides pass through the center of the SecY complex. The strongest cross-links were observed with residues that would form a constriction in an hourglass-shaped pore. This suggests that the channel makes only limited contact with a translocating polypeptide, thus minimizing the energy required for translocation.
authors.affiliation: Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Kurt S
authors.initials: KS
authors.lastname: Cannon
authors.forename: Eran
authors.initials: E
authors.lastname: Or
authors.forename: William M
authors.initials: WM
authors.lastname: Clemons
authors.forename: Yoko
authors.initials: Y
authors.lastname: Shibata
authors.forename: Tom A
authors.initials: TA
authors.lastname: Rapoport
mesh_terms: D019943:Amino Acid Substitution; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry*; D004926:Escherichia coli / Q000737:chemistry* / Q000502:physiology; D029968:Escherichia coli Proteins / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D021381:Protein Transport / Q000502:physiology; D000069816:SEC Translocation Channels
chemical_list: D004220:Disulfides; D029968:Escherichia coli Proteins; D010455:Peptides; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli; D003545:Cysteine