CTP and parS coordinate ParB partition complex dynamics and ParA-ATPase activation for ParABS-mediated DNA...

Area of Science:

• Molecular Biology
• Microbiology
• Genetics

Background:

• ParABS partition systems are essential for bacterial chromosome and plasmid segregation.
• These systems involve a DNA site (parS) and two proteins: ParB (a CTPase) and ParA (an ATPase).
• The mechanism by which ParB activates ParA's ATPase activity remained unclear.

Purpose of the Study:

• To elucidate the CTP- and parS-modulated assembly of ParA-ParB complexes.
• To understand how ParB activates ParA's ATPase activity for DNA segregation.

Main Methods:

• Biochemical assays to study ParA-ParB complex assembly and ATPase activity.
• Magnetic tweezers experiments to observe DNA-protein interactions and complex formation.

Main Results:

• DNA-bound ParA-ATP dimers are activated for hydrolysis upon interaction with ParB N-terminal domains.
• CTP or parS individually enhance ParA's ATPase rate, but not complex assembly.
• Together, parS and CTP accelerate ParA-ParB assembly without further increasing ATPase rate.
• CTP promotes multiple ParB loading onto parS-DNA, forming condensed assemblies.

Conclusions:

• ParB binding to parS, modulated by CTP, drives the formation of functional partition complexes.
• ParB adopts a conformation that enhances interactions with both ParA and other ParB proteins.
• These enhanced interactions facilitate efficient DNA segregation by bacterial partition systems.