CD of single-stranded, double-stranded, and G-quartet nucleic acids in complexes with a single-stranded DNA-binding...

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• The Ff group of bacterial viruses utilizes a single-stranded DNA binding protein, g5p.
• Circular Dichroism (CD) spectroscopy is a valuable tool for studying protein-nucleic acid interactions.

Purpose of the Study:

• To review CD studies of the g5p protein and its interactions with nucleic acids.
• To elucidate the structural changes in g5p upon nucleic acid binding using CD spectroscopy.

Main Methods:

• Circular Dichroism (CD) spectroscopy was employed to analyze g5p.
• Mutagenesis studies identified key tyrosine residues involved in DNA binding.
• SELEX (Systematic Evolution of Ligands by Exponential Enrichment) was used to identify preferred g5p binding sequences.

Main Results:

• The CD spectrum of g5p is characterized by a positive tyrosine La band at 229 nm.
• Nucleic acid binding significantly perturbs the g5p CD spectrum, primarily due to tyrosine Y34.
• CD titrations revealed two distinct binding modes of g5p at physiological ionic strength.
• SELEX identified a G-rich sequence with G-quadruplex properties, which is maintained within g5p-DNA complexes.

Conclusions:

• Tyrosine Y34 plays a critical role in the CD spectral changes of g5p upon nucleic acid binding.
• g5p exhibits complex binding behavior with nucleic acids, including G-quadruplex structures.
• CD spectroscopy provides insights into the structural dynamics of g5p during DNA complex formation.