TEMPERATURE MODULATION OF LUTEIN-LYSOZYME HYDROPHOBIC-HYDROPHILIC INTERACTION BALANCE

Lutein (Lut) is one of the main xanthophylls present in the human macula, recognized by reducing the risk of age-related macular degeneration. The Lut supplementation is effective for many improvements in cases of eye diseases; however, after its extraction from its various sources, Lut has great chemical instability, reducing its antioxidant functionality. Therefore, the formation of nanocomplexes between Lut and Lys is an alternative method of transporting Lut and improving its chemical stability. To optimize the formation of the Lut-Lys complex, binding assays were performed in the temperature range of 12‒28 °C, at pH 7.4, using real-time and label-free surface plasmon resonance (SPR). Kinetics analysis showed that about 2000 Lut-Lys complexes are formed per second, of which 36% dissociate per second. The results were interpreted based on transition state theory (TST), which makes possible to determine the energetic parameters associated with the formation of the activated complex along the binding path. The speed of formation of the activated complex was not affected by temperature (∆^‡ G_a^0≅53 and ∆^‡ G_d^0≅74 kJ.mol‒1); however, there was a critical temperature (T≅18.36 °C), below which the hydrophobic forces dominated and above which hydrophilic interactions, such as van der Waals (VW) and hydrogen bonds (HYD), determined the process (E_(act,a)=22.12 to-59.34 kJ.mol‒1 and E_(act,d)=10.41 to-22.64 kJ.mol‒1). The stability of the thermodynamic stable complex was temperature-independent (〖∆G〗^0≅-21 kJ mol‒1); but, the relative hydrophobic/hydrophilic contributions to the enthalpy and entropy changes for the formation of this complex were dependent on the temperature (〖∆H〗^0=11.72 to-36.71 kJ.mol‒1 and 〖T∆S〗^0 =32.11 to-15.54 kJ.mol‒1). The proportional relationship between 〖∆H〗^0 and 〖T∆S〗^0 was attributed to a cooperative process between the hydrophobic (mainly due to desolvation and conformational Lys-site fitting) and hydrophilic interactions (VW and HYD). The SPR data provide useful insight into the discovery of potential lutein-protein nanocarriers.