Molecular Anatomy of ParA-ParA and ParA-ParB Interactions during Plasmid Partitioning

Area of Science:

• Molecular Biology
• Microbiology
• Genetics

Background:

• Inc18 plasmids from Firmicutes bacteria utilize parS sites and two proteins, ParA-like (δ2) and ParB-like (ω2), for accurate DNA segregation.
• The ω2 protein binds to parS DNA, forming a left-handed helix and interacting with δ2.
• The δ2 protein interacts with ω2 and, when bound to ATP, associates with non-specific DNA (nsDNA), forming clusters.

Purpose of the Study:

• To map the interacting domains within the δ2 protein responsible for its interactions with ω2 and other δ2 molecules.
• To elucidate the role of the δ2 non-specific DNA binding domain in the segregation mechanism.
• To understand the mechanism of ATP hydrolysis stimulation and subsequent protein release from DNA.

Main Methods:

• Protein interaction domain mapping of δ2.
• Analysis of δ2 interactions with ω2, other δ2 proteins, ATP, and DNA.
• Assays to measure ATP hydrolysis stimulation and protein-DNA binding.

Main Results:

• Identified distinct but adjacent domains in δ2 for ω2·δ2 and δ2·δ2 interactions.
• The δ2 non-specific DNA binding domain is crucial for stimulating ω2·parS-mediated ATP hydrolysis.
• Proposed a model where δ2 binds ATP, nsDNA, and ω2·parS, inducing a structural transition for activation.

Conclusions:

• The δ2 protein undergoes an 'activated' state upon binding to ATP, nsDNA, and ω2·parS.
• This activation overcomes inhibition of ATP hydrolysis, leading to protein release from nsDNA.
• The findings provide mechanistic insights into the faithful segregation of inc18 plasmids.