Dynamic structural states of ClpB involved in its disaggregation function

Area of Science:

• Molecular biology
• Biophysics
• Protein biochemistry

Background:

• ClpB, an AAA+ ATPase, disaggregates toxic protein aggregates with Hsp70.
• ClpB functions as a ring-shaped hexamer that threads substrates through its central pore.
• The structural dynamics of ClpB during protein disaggregation remain poorly understood.

Purpose of the Study:

• To elucidate the function-related structural dynamics of ClpB.
• To gain mechanistic insight into the protein disaggregation process mediated by ClpB.
• To visualize ClpB conformational changes during ATP hydrolysis.

Main Methods:

• High-speed atomic force microscopy (HS-AFM) was employed to directly visualize ClpB.
• HS-AFM movies captured dynamic conformational transitions of the ClpB hexamer.
• Analysis of Walker-motif mutants and specific mutations (repressed, hyperactive) provided insights into ClpB function.

Main Results:

• HS-AFM revealed massive conformational changes in the ClpB hexameric ring during ATP hydrolysis, including transitions to spiral and half-spiral forms.
• ATP binding and hydrolysis were shown to be critical for ClpB oligomer formation and structural dynamics.
• Distinct oligomeric forms were observed for repressed and hyperactive ClpB mutants.

Conclusions:

• The study provides a comprehensive view of ATP-driven oligomeric-state transitions in ClpB.
• These dynamic transitions are essential for ClpB's ability to disaggregate protein aggregates.
• Visualizing ClpB's structural dynamics offers mechanistic insights into protein quality control.