title: Structural basis of signal sequence surveillance and selection by the SRP-FtsY complex.
abstract: Signal-recognition particle (SRP)-dependent targeting of translating ribosomes to membranes is a multistep quality-control process. Ribosomes that are translating weakly hydrophobic signal sequences can be rejected from the targeting reaction even after they are bound to the SRP. Here we show that the early complex, formed by Escherichia coli SRP and its receptor FtsY with ribosomes translating the incorrect cargo EspP, is unstable and rearranges inefficiently into subsequent conformational states, such that FtsY dissociation is favored over successful targeting. The N-terminal extension of EspP is responsible for these defects in the early targeting complex. The cryo-electron microscopy structure of this 'false' early complex with EspP revealed an ordered M domain of SRP protein Ffh making two ribosomal contacts, and the NG domains of Ffh and FtsY forming a distorted, flexible heterodimer. Our results provide a structural basis for SRP-mediated signal-sequence selection during recruitment of the SRP receptor.
authors.affiliation: European Molecular Biology Laboratory, Grenoble Outstation, Grenoble, France.
authors.forename: Ottilie
authors.initials: O
authors.lastname: von Loeffelholz
authors.forename: Kèvin
authors.initials: K
authors.lastname: Knoops
authors.forename: Aileen
authors.initials: A
authors.lastname: Ariosa
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.forename: Manikandan
authors.initials: M
authors.lastname: Karuppasamy
authors.forename: Karine
authors.initials: K
authors.lastname: Huard
authors.forename: Guy
authors.initials: G
authors.lastname: Schoehn
authors.forename: Imre
authors.initials: I
authors.lastname: Berger
authors.forename: Shu-ou
authors.initials: SO
authors.lastname: Shan
authors.forename: Christiane
authors.initials: C
authors.lastname: Schaffitzel
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D020285:Cryoelectron Microscopy; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry; D011487:Protein Conformation; D021382:Protein Sorting Signals; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000737:chemistry / Q000378:metabolism; D018271:Signal Recognition Particle / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C087406:FtsY protein, Bacteria; D046912:Multiprotein Complexes; D021382:Protein Sorting Signals; D018160:Receptors, Cytoplasmic and Nuclear; D018271:Signal Recognition Particle; C107189:EspP protein, E coli; D012697:Serine Endopeptidases
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