Lactoferrin/κ-Carrageenan Interactions: Thermodynamic and Kinetic Insights through Surface Plasmon Resonance and Steady-State Fluorescence

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 ≤ ΔGFSo ≤ −46.15 kJ mol–1) and is predominantly enthalpy-driven (ΔHFSo = −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 ≤ ΔGa‡ ≤ 38.52 kJ mol–1) than through dissociation of the thermodynamically stable complex (77.61 ≤ ΔGd‡ ≤ 81.62 kJ mol–1). Consistent with these findings, the energetic barrier for dissociation (Ed–298.2 K‡ = 96.46 kJ mol–1) was higher than for association (Ea–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.