ClpA mediates directional translocation of substrate proteins into the ClpP protease

Area of Science:

• Molecular biology
• Protein degradation
• Biochemistry

Background:

• Intracellular protein degradation relies on ATP-dependent chaperone-protease complexes.
• The ClpA chaperone unfolds substrates and directs their translocation into the ClpP protease.
• The narrow axial passageway of ClpP suggests a directional threading mechanism.

Purpose of the Study:

• To investigate the directionality of substrate protein translocation into the ClpP protease mediated by the ClpA chaperone.
• To determine if substrate proteins are threaded into ClpP in a specific orientation.

Main Methods:

• Utilized two substrate proteins with the ssrA recognition element, labeled with fluorescent probes at either the N-terminus or C-terminus.
• Measured time-dependent changes in fluorescence anisotropy and resonance energy transfer (FRET).
• Monitored substrate translocation from ClpA into ClpP using FRET between a donor in ClpP and acceptor probes on the substrate.

Main Results:

• Observed earlier energy transfer (2-4 s sooner) for C-terminally labeled substrates compared to N-terminally labeled ones.
• Demonstrated directional translocation of substrate proteins into the ClpP proteolytic chamber.
• Indicated that the C-terminus of the substrate protein enters ClpP first.

Conclusions:

• Substrate translocation into the ClpP protease is a directional process.
• The C-terminus of the substrate protein is translocated into ClpP before the N-terminus.
• This directional threading mechanism is crucial for efficient protein degradation by the ClpAP complex.