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Abstract

Ribosome-associated Trigger factor (TF) is the first molecular chaperone to bind to nascent polypeptides in bacteria. The contribution of co-translational chaperone function is yet poorly understood. Using fluorescence spectroscopy to monitor, in real time, TF function and structural rearrangements, the present study investigates how TF interacts with ribosomes and translating polypeptides. Binding to the ribosome stabilizes an open, activated conformation of TF. Conformationally activated TF can stay associated with its nascent polypeptide substrate beyond ribosome departure. The occurence of hydrophobic motifs in the translating polypeptide correlates with the duration of TF-substrate interaction, leading to prolonged interaction with a high aggregation propensity. These findings can explain the contribution of TF in preventing protein misfolding and reveal an exquisitely regulated interaction cycle of TF with ribosome-nascent chain complexes.