title: Real-time observation of trigger factor function on translating ribosomes.
abstract: The contribution of co-translational chaperone functions to protein folding is poorly understood. Ribosome-associated trigger factor (TF) is the first molecular chaperone encountered by nascent polypeptides in bacteria. Here we show, using fluorescence spectroscopy to monitor TF function and structural rearrangements in real time, that TF interacts with ribosomes and translating polypeptides in a dynamic reaction cycle. Ribosome binding stabilizes TF in an open, activated conformation. Activated TF departs from the ribosome after a mean residence time of approximately 10 s, but may remain associated with the elongating nascent chain for up to 35 s, allowing entry of a new TF molecule at the ribosome docking site. The duration of nascent-chain interaction correlates with the occurrence of hydrophobic motifs in translating polypeptides, reflecting a high aggregation propensity. These findings can explain how TF prevents misfolding events during translation and may provide a paradigm for the regulation of nucleotide-independent chaperones.
authors.affiliation: Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany.
authors.forename: Christian M
authors.initials: CM
authors.lastname: Kaiser
authors.forename: Hung-Chun
authors.initials: HC
authors.lastname: Chang
authors.forename: Vishwas R
authors.initials: VR
authors.lastname: Agashe
authors.forename: Sathish K
authors.initials: SK
authors.lastname: Lakshmipathy
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Etchells
authors.forename: Manajit
authors.initials: M
authors.lastname: Hayer-Hartl
authors.forename: F Ulrich
authors.initials: FU
authors.lastname: Hartl
authors.forename: José M
authors.initials: JM
authors.lastname: Barral
mesh_terms: D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry; D019696:Peptidylprolyl Isomerase / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D014176:Protein Biosynthesis; D017510:Protein Folding; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; D010455:Peptides; C403324:trigger factor, E coli; D019696:Peptidylprolyl Isomerase