Lactoferrin/κ-Carrageenan Interactions: Thermodynamic and Kinetic Insights through Surface Plasmon Resonance and...

Protein-polysaccharide complexes play important roles in a wide range of technological applications. To elucidate the molecular interactions governing the formation of bovine lactoferrin (BLF)-κ-carrageenan (κCG) bionanostructures, the thermodynamic and kinetic parameters of BLF-κCG binding were determined using Steady-state fluorescence (FS) and surface plasmon resonance (SPR) spectroscopies. Formation of a 1:1 BLF-κCG complex is thermodynamically favorable at equilibrium (-47.00 ≤ ΔG _FS ^o ≤ -46.15 kJ mol^-1) and is predominantly enthalpy-driven (ΔH _FS ^o = -57.43 kJ mol^-1). Kinetic analysis by SPR revealed that the interaction proceeds through a transition complex ([BLF - κCG]^‡), with complex formation occurring more rapidly through association of the free molecules (32.53 ≤ ΔG _a ^‡ ≤ 38.52 kJ mol^-1) than through dissociation of the thermodynamically stable complex (77.61 ≤ ΔG _d ^‡ ≤ 81.62 kJ mol^-1). Consistent with these findings, the energetic barrier for dissociation (E _d-298.2 K ^‡ = 96.46 kJ mol^-1) was higher than for association (E _a-298.2 K ^‡ = 42.88 kJ mol^-1). Increasing the ionic strength altered the BLF-κCG interaction mechanism, converting the binding process from a multistep pathway to a single-step process.