Single-stranded DNA-binding protein complex from Helicobacter pylori suggests an ssDNA-binding surface

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Single-stranded DNA-binding proteins (SSBs) are essential for DNA replication, recombination, and repair.
• SSBs possess an N-terminal DNA-binding domain and a C-terminal tail for protein interactions.

Purpose of the Study:

• To isolate and characterize the ssDNA-binding properties of Helicobacter pylori SSB (HpSSB).
• To determine the crystal structure of HpSSB complexed with ssDNA to elucidate its binding mechanism.

Main Methods:

• Fluorescence titration and electrophoretic mobility shift assay (EMSA) were used to analyze ssDNA-binding characteristics.
• X-ray crystallography was employed to determine the structure of a truncated HpSSB (HpSSBc) bound to ssDNA.

Main Results:

• HpSSB exhibited a cooperative affinity of 5.4x10(7) M(-1) for ssDNA, binding approximately 25-30 nucleotides.
• The crystal structure revealed that HpSSBc forms a tetramer, with ssDNA wrapping around it via aromatic and basic residues.

Conclusions:

• HpSSB demonstrates significant ssDNA-binding capability, essential for its biological functions in H. pylori.
• The determined structure provides a molecular basis for understanding HpSSB-ssDNA interactions and its role in DNA metabolism.