title: Conformation of the signal recognition particle in ribosomal targeting complexes.
abstract: The bacterial signal recognition particle (SRP) binds to ribosomes synthesizing inner membrane proteins and, by interaction with the SRP receptor, FtsY, targets them to the translocon at the membrane. Here we probe the conformation of SRP and SRP protein, Ffh, at different stages of targeting by measuring fluorescence resonance energy transfer (FRET) between fluorophores placed at various positions within SRP. Distances derived from FRET indicate that SRP binding to nontranslating ribosomes triggers a global conformational change of SRP that facilitates binding of the SRP receptor, FtsY. Binding of SRP to a signal-anchor sequence exposed on a ribosome-nascent chain complex (RNC) causes a further change of the SRP conformation, involving the flexible part of the Ffh(M) domain, which increases the affinity for FtsY of ribosome-bound SRP up to the affinity exhibited by the isolated NG domain of Ffh. This indicates that in the RNC-SRP complex the Ffh(NG) domain is fully exposed for binding FtsY to form the targeting complex. Binding of FtsY to the RNC-SRP complex results in a limited conformational change of SRP, which may initiate subsequent targeting steps.
authors.affiliation: Institute of Molecular Biology, University of Witten/Herdecke, 58448 Witten, Germany.
authors.forename: Iwona A
authors.initials: IA
authors.lastname: Buskiewicz
authors.forename: Johannes
authors.initials: J
authors.lastname: Jöckel
authors.forename: Marina V
authors.initials: MV
authors.lastname: Rodnina
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wintermeyer
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D012329:RNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism*; D018271:Signal Recognition Particle / Q000737:chemistry* / Q000378:metabolism
chemical_list: C409968:4.5S RNA; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C082931:Ffh protein, E coli; D012329:RNA, Bacterial; D018271:Signal Recognition Particle