Real time observation of TF function on translating ribosomes

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.