DNA replication initiation in Bacillus subtilis: structural and functional characterization of the essential...

Area of Science:

• Bacteriology
• Molecular Biology
• Genetics

Background:

• The homotetrameric DnaD protein is crucial for DNA replication initiation in low G+C content gram-positive bacteria.
• DnaD interacts with the master replication initiation protein DnaA at the oriC, but the structural and functional details of this interaction remain unclear.
• Conflicting studies suggested either the N-terminal (DDBH1) or C-terminal (DDBH2) domain of DnaD interacts with DnaA.

Purpose of the Study:

• To elucidate the structural and functional details of the DnaD-DnaA interaction during bacterial replication initiation.
• To determine which domains of DnaD interact with DnaA and how this interaction affects DNA.
• To understand the collaborative mechanism of DnaA and DnaD at the oriC.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to study protein-protein interactions and structures.
• Single-molecule Förster Resonance Energy Transfer (smFRET) to observe dynamic filament remodeling.
• Bacterial and yeast two-hybrid assays to map interaction domains.

Main Results:

• Both DDBH1 and DDBH2 domains of DnaD interact with domain I of DnaA.
• Two distinct conformational states were observed for the DDBH2-DnaA domain I complex.
• The DNA-binding site of DnaD is separate from its DnaA-interaction site, allowing simultaneous binding.
• DnaD remodels DnaA-DNA filaments, inducing stretching or untwisting, independent of its DNA-binding activity.

Conclusions:

• DnaD and DnaA collaborate at the oriC to initiate DNA replication.
• DnaD's role involves remodeling DnaA-DNA filaments, likely facilitating local DNA unwinding.
• This interaction is critical for understanding the fundamental mechanisms of bacterial DNA replication initiation.