title: Structure of the E. coli protein-conducting channel bound to a translating ribosome.
abstract: Secreted and membrane proteins are translocated across or into cell membranes through a protein-conducting channel (PCC). Here we present a cryo-electron microscopy reconstruction of the Escherichia coli PCC, SecYEG, complexed with the ribosome and a nascent chain containing a signal anchor. This reconstruction shows a messenger RNA, three transfer RNAs, the nascent chain, and detailed features of both a translocating PCC and a second, non-translocating PCC bound to mRNA hairpins. The translocating PCC forms connections with ribosomal RNA hairpins on two sides and ribosomal proteins at the back, leaving a frontal opening. Normal mode-based flexible fitting of the archaeal SecYEbeta structure into the PCC electron microscopy densities favours a front-to-front arrangement of two SecYEG complexes in the PCC, and supports channel formation by the opening of two linked SecY halves during polypeptide translocation. On the basis of our observation in the translocating PCC of two segregated pores with different degrees of access to bulk lipid, we propose a model for co-translational protein translocation.
authors.affiliation: Howard Hughes Medical Institute, Health Research Inc. at the Wadsworth Center, Empire State Plaza, Albany, New York 12201-0509, USA.
authors.forename: Kakoli
authors.initials: K
authors.lastname: Mitra
authors.forename: Christiane
authors.initials: C
authors.lastname: Schaffitzel
authors.forename: Tanvir
authors.initials: T
authors.lastname: Shaikh
authors.forename: Florence
authors.initials: F
authors.lastname: Tama
authors.forename: Simon
authors.initials: S
authors.lastname: Jenni
authors.forename: Charles L
authors.initials: CL
authors.lastname: Brooks
authors.forename: Nenad
authors.initials: N
authors.lastname: Ban
authors.forename: Joachim
authors.initials: J
authors.lastname: Frank
mesh_terms: D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D020285:Cryoelectron Microscopy; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D018583:Pliability; D011485:Protein Binding; D014176:Protein Biosynthesis; D020836:Protein Structure, Quaternary; D021381:Protein Transport; D012270:Ribosomes / Q000378:metabolism*; D000069816:SEC Translocation Channels
chemical_list: D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D000069816:SEC Translocation Channels; C065493:SecE protein, E coli; C088616:SecG protein, E coli; C057841:SecY protein, E coli