Structural dynamics of the MecA-ClpC complex: a type II AAA+ protein unfolding machine

Area of Science:

• Molecular biology
• Structural biology
• Biochemistry

Background:

• The MecA-ClpC complex is a type II AAA+ molecular machine in bacteria.
• It mediates the unfolding and degradation of substrates like ComK and ComS via the ClpP protease.
• The detailed mechanism of substrate unfolding and translocation by AAA+ proteins remains incompletely understood.

Purpose of the Study:

• To elucidate the dynamic mechanism of the MecA-ClpC unfoldase.
• To provide structural insights into substrate unfolding and translocation by type II AAA+ hexamers.

Main Methods:

• Cryoelectron microscopy (cryo-EM) was used to capture four distinct structures of the MecA-ClpC complex.
• Structural analysis focused on variations in nucleotide binding states and their impact on complex conformation.
• Biochemical data complemented structural findings.

Main Results:

• Nucleotide binding and hydrolysis were shown to modulate the MecA-ClpC complex structure, affecting ring opening, pore loop positioning, and inter-ring rotation.
• Four distinct structural states were identified, likely representing snapshots of the unfolding cycle.
• Allosteric communication between the two AAA+ rings was revealed, essential for efficient substrate processing.

Conclusions:

• The study provides key mechanistic insights into the dynamic cycle of the MecA-ClpC unfoldase.
• Concerted action of the two AAA+ rings is critical for substrate unfolding and translocation.
• These findings establish a foundation for understanding the structural dynamics of general type II AAA+ hexamers.