Translocation pathway of protein substrates in ClpAP protease

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Intracellular protein degradation is crucial for cellular function and tightly regulated by ATP-dependent proteases.
• Multicomponent enzymes like ClpAP utilize chaperone-like ATPases to unfold and deliver protein substrates for degradation.

Purpose of the Study:

• To characterize the structural mechanism of substrate translocation by the ClpAP protease complex using cryo-electron microscopy.
• To visualize the interaction of the ClpAP complex with its model substrate, bacteriophage P1 protein RepA.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to study ClpAP complexes.
• Interactions with the model substrate RepA were analyzed in the presence of ATPgammaS and ATP.
• A ClpP mutant with an occupied digestion chamber was used to trap translocation intermediates.

Main Results:

• RepA dimers bind to ClpA in ATPgammaS-stabilized complexes.
• Upon ATP addition, RepA translocates into the ClpP digestion chamber with minimal ClpAP structural changes.
• Cryo-EM of a ClpP mutant revealed intermediate binding sites for RepA within ClpP, suggesting a stepwise translocation pathway.

Conclusions:

• The ClpAP complex translocates unfolded RepA substrates through a defined pathway.
• Substrate translocation occurs without major conformational changes in the ClpA hexamer.
• Intermediate accumulation sites within ClpP highlight the dynamic nature of protein translocation and degradation.