Solution structure and small angle scattering analysis of TraI (381-569).

Area of Science:

• Structural biology
• Molecular biology
• Bacteriology

Background:

• TraI is essential for bacterial conjugation, mediating plasmid DNA transfer.
• The central domains of TraI, responsible for DNA binding and unwinding, remain structurally uncharacterized.
• Previous studies determined structures of TraI's N- and C-terminal domains.

Purpose of the Study:

• To structurally characterize the central, unexplored domains of the F plasmid TraI protein.
• To identify the single-stranded DNA (ssDNA) binding site within TraI.
• To elucidate the structural basis for TraI's helicase activity and domain interactions.

Main Methods:

• High-resolution solution structure determination of a TraI fragment (residues 381-569).
• Bioinformatic analysis comparing TraI domain structures to known helicases.
• Biochemical assays to investigate domain linkage and cooperativity.

Main Results:

• The ssDNA binding site was localized to residues 381-858.
• The N-terminal portion of the ssDNA binding domain (residues 381-569) was structurally characterized, revealing a RecD-like fold.
• A linker region was identified connecting the nickase and ssDNA binding domains, potentially explaining negative cooperativity.

Conclusions:

• The structure of the TraI ssDNA binding domain suggests an evolutionary origin from a duplicated RecD-like domain.
• Domain duplication and specialization likely shaped TraI's functional architecture.
• The linker sequence provides a physical basis for the interplay between TraI's nickase and ssDNA binding activities.