title: Ribosome-SRP-FtsY cotranslational targeting complex in the closed state.
abstract: The signal recognition particle (SRP)-dependent pathway is essential for correct targeting of proteins to the membrane and subsequent insertion in the membrane or secretion. In Escherichia coli, the SRP and its receptor FtsY bind to ribosome-nascent chain complexes with signal sequences and undergo a series of distinct conformational changes, which ensures accurate timing and fidelity of protein targeting. Initial recruitment of the SRP receptor FtsY to the SRP-RNC complex results in GTP-independent binding of the SRP-FtsY GTPases at the SRP RNA tetraloop. In the presence of GTP, a closed state is adopted by the SRP-FtsY complex. The cryo-EM structure of the closed state reveals an ordered SRP RNA and SRP M domain with a signal sequence-bound. Van der Waals interactions between the finger loop and ribosomal protein L24 lead to a constricted signal sequence-binding pocket possibly preventing premature release of the signal sequence. Conserved M-domain residues contact ribosomal RNA helices 24 and 59. The SRP-FtsY GTPases are detached from the RNA tetraloop and flexible, thus liberating the ribosomal exit site for binding of the translocation machinery.
authors.affiliation: European Molecular Biology Laboratory, Grenoble 38042, France; Unit for Virus Host-Cell Interactions, Université Grenoble Alpes, European Molecular Biology Laboratory, CNRS, Grenoble 38042, France;
authors.forename: Ottilie
authors.initials: O
authors.lastname: von Loeffelholz
authors.affiliation: European Molecular Biology Laboratory, Grenoble 38042, France; Unit for Virus Host-Cell Interactions, Université Grenoble Alpes, European Molecular Biology Laboratory, CNRS, Grenoble 38042, France;
authors.forename: Qiyang
authors.initials: Q
authors.lastname: Jiang
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125; and.
authors.forename: Aileen
authors.initials: A
authors.lastname: Ariosa
authors.affiliation: European Molecular Biology Laboratory, Grenoble 38042, France; Unit for Virus Host-Cell Interactions, Université Grenoble Alpes, European Molecular Biology Laboratory, CNRS, Grenoble 38042, France;
authors.forename: Manikandan
authors.initials: M
authors.lastname: Karuppasamy
authors.affiliation: European Molecular Biology Laboratory, Grenoble 38042, France; Unit for Virus Host-Cell Interactions, Université Grenoble Alpes, European Molecular Biology Laboratory, CNRS, Grenoble 38042, France;
authors.forename: Karine
authors.initials: K
authors.lastname: Huard
authors.affiliation: European Molecular Biology Laboratory, Grenoble 38042, France; Unit for Virus Host-Cell Interactions, Université Grenoble Alpes, European Molecular Biology Laboratory, CNRS, Grenoble 38042, France; School of Biochemistry, University of Bristol, Bristol BS8 1TD, United Kingdom.
authors.forename: Imre
authors.initials: I
authors.lastname: Berger
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125; and.
authors.forename: Shu-ou
authors.initials: SO
authors.lastname: Shan
authors.affiliation: European Molecular Biology Laboratory, Grenoble 38042, France; Unit for Virus Host-Cell Interactions, Université Grenoble Alpes, European Molecular Biology Laboratory, CNRS, Grenoble 38042, France; School of Biochemistry, University of Bristol, Bristol BS8 1TD, United Kingdom schaffitzel@embl.fr.
authors.forename: Christiane
authors.initials: C
authors.lastname: Schaffitzel
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D003001:Cloning, Molecular; D020285:Cryoelectron Microscopy; D004926:Escherichia coli / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D008958:Models, Molecular; D011485:Protein Binding; D014176:Protein Biosynthesis; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D018271:Signal Recognition Particle
chemical_list: D001426:Bacterial Proteins; C087406:FtsY protein, Bacteria; D021382:Protein Sorting Signals; D018160:Receptors, Cytoplasmic and Nuclear; D018271:Signal Recognition Particle
keywords: protein targeting; ribosome; signal recognition particle; signal sequence; single-particle electron cryomicroscopy