title: Compaction of a prokaryotic signal-anchor transmembrane domain begins within the ribosome tunnel and is stabilized by SRP during targeting.
abstract: Cotranslational targeting of membrane proteins is mediated by the universally conserved signal recognition particle (SRP). In eukaryotes, SRP attenuates translation during targeting; however, in prokaryotes, a simplified SRP is believed to carry out targeting during continuing translation. Here, we show a detailed stepwise analysis of the targeting of subunit c of the F(0) component of the bacterial ATP synthase (F(0)c) to the inner membrane. We show that the first transmembrane (TM) signal-anchor domain of F(0)c forms a compacted structure within the distal portion of the ribosome tunnel. This structure is formed just prior to the interaction with SRP. In the absence of SRP this structure is lost as the TM domain exits the tunnel; however in the presence of SRP it is stabilized. Our results suggest differences in early protein folding of substrates for prokaryotic SRP-dependent membrane protein targeting pathways, from that of eukaryotic SRP targeting. These results imply that early TM domain recognition by targeting factors acts to ensure that the efficiency of membrane targeting is maintained.
authors.affiliation: Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Robinson
authors.forename: Jane E
authors.initials: JE
authors.lastname: Findlay
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: Woolhead
mesh_terms: D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D014176:Protein Biosynthesis; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D006180:Proton-Translocating ATPases / Q000737:chemistry* / Q000378:metabolism*; D054681:Ribosome Subunits, Large, Bacterial / Q000378:metabolism / Q000648:ultrastructure; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D018271:Signal Recognition Particle / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D018271:Signal Recognition Particle; D006180:Proton-Translocating ATPases