title: Regulation of cargo recognition, commitment, and unloading drives cotranslational protein targeting.
abstract: Efficient and accurate protein localization is essential to cells and requires protein-targeting machineries to both effectively capture the cargo in the cytosol and productively unload the cargo at the membrane. To understand how these challenges are met, we followed the interaction of translating ribosomes during their targeting by the signal recognition particle (SRP) using a site-specific fluorescent probe in the nascent protein. We show that initial recruitment of SRP receptor (SR) selectively enhances the affinity of SRP for correct cargos, thus committing SRP-dependent substrates to the pathway. Real-time measurement of cargo transfer from the targeting to translocation machinery revealed multiple factors that drive this event, including GTPase rearrangement in the SRP-SR complex, stepwise displacement of SRP from the ribosome and signal sequence by SecYEG, and elongation of the nascent polypeptide. Our results elucidate how active and sequential regulation of the SRP-cargo interaction drives efficient and faithful protein targeting.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125 sshan@caltech.edu ishu@iiserb.ac.in.
authors.forename: Ishu
authors.initials: I
authors.lastname: Saraogi
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125.
authors.forename: David
authors.initials: D
authors.lastname: Akopian
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125 sshan@caltech.edu ishu@iiserb.ac.in.
authors.forename: Shu-Ou
authors.initials: SO
authors.lastname: Shan
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D003460:Crystallization; D003600:Cytosol / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer; D005456:Fluorescent Dyes; D020558:GTP Phosphohydrolases / Q000378:metabolism; D005786:Gene Expression Regulation; D010455:Peptides / Q000378:metabolism; D014176:Protein Biosynthesis; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D018000:Receptors, Peptide / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism; D018271:Signal Recognition Particle / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D005456:Fluorescent Dyes; C087406:FtsY protein, Bacteria; D010455:Peptides; D021382:Protein Sorting Signals; D018160:Receptors, Cytoplasmic and Nuclear; D018000:Receptors, Peptide; D018271:Signal Recognition Particle; C036318:signal peptide receptor; D020558:GTP Phosphohydrolases