Lactoferrin-phenothiazine dye interactions: Thermodynamic and kinetic approach

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Biopolymer-ligand molecular recognition is fundamental to life.
• Understanding protein-ligand binding kinetics and energetics is crucial for biological system modulation.
• Methylene blue (MB) and azure A (AZA) are photosensitive dyes with potential biological applications.

Purpose of the Study:

• To investigate the binding thermodynamics and kinetics of methylene blue (MB) and azure A (AZA) with bovine lactoferrin (BLF).
• To elucidate the role of hydrophobic and electrostatic interactions in BLF-dye complex formation and dissociation.
• To assess the influence of dye chemical structure on binding parameters.

Main Methods:

• Surface Plasmon Resonance (SPR) for real-time binding analysis.
• Fluorescence Spectroscopy for probing molecular interactions.
• Isothermal Titration Microcalorimetry (ITC) for determining thermodynamic parameters.

Main Results:

• BLF-AZA binding exhibited higher thermodynamic parameters (ΔG, ΔH, TΔS) than BLF-MB binding, indicating stronger interactions.
• Hydrophobic interactions were found to dominate over electrostatic repulsion in promoting BLF-dye binding.
• Complex dissociation kinetics were significantly influenced by the number of methyl groups on the dyes, while association kinetics were less affected.

Conclusions:

• The binding affinity and dissociation rates of BLF-dye complexes are modulated by dye structure, particularly the degree of methylation.
• These findings provide insights into kinetic parameter-controlled binding processes.
• The study offers valuable data for optimizing the application of photosensitive dyes like MB and AZA in biological systems.