Fast dynamics shape the function of the AAA+ machine ClpB: lessons from single-molecule FRET spectroscopy

Area of Science:

• Biochemistry
• Structural Biology
• Protein Dynamics

Background:

• Proteins exhibit tertiary-structure dynamics on microsecond to sub-millisecond timescales.
• Caseinolytic peptidase B (ClpB) is a AAA+ disaggregation machine crucial for protein rescue.
• Understanding ClpB's dynamics is key to its function in cellular protein homeostasis.

Purpose of the Study:

• To investigate the relationship between ultrafast domain motions and ClpB function.
• To elucidate the role of specific ClpB domains in its disaggregation mechanism.
• To propose a model for ClpB activity based on observed dynamics.

Main Methods:

• Single-molecule Förster Resonance Energy Transfer (smFRET) spectroscopy was employed.
• The dynamics of essential structural elements within ClpB were captured.
• Perturbations were used to study pore loop responses.

Main Results:

• The middle domain of ClpB exhibits ultrafast toggling between states, suggesting tunable switching.
• The N-terminal domain restricts middle domain conformational space, preventing spurious activation.
• Microsecond dynamics of pore loops indicate a Brownian-ratchet mechanism for translocation.

Conclusions:

• A two-time-scale model for ClpB activity is proposed, integrating fast dynamics with slower ATP hydrolysis.
• Ultrafast conformational dynamics modulate slower functional steps in ClpB.
• Further research on protein dynamics will illuminate their broader role in protein function.