Noncovalent interactions of bovine α-lactalbumin with green tea polyphenol, epigalocatechin-3-gallate

A review of methods used for investigation of protein–phenolic compound interactions

“…The formation of complexes with phenolic compounds also affects the secondary structure of the protein. Therefore, quantitative changes in the proportion of a-helices chains and b-sheets in proteins as a result of attachment of phenolic compounds can be monitored using circular dichroism (CD) (Rawel et al, 2002a,b;Kanakis et al, 2011;Wu et al, 2013;Vesic et al, 2015;Al-Hanish et al, 2016). For example, CD spectrum of human serum albumin exhibits two negative bands at 208 and 222 nm, which are typical for ahelix structure of the protein.…”

“…The proteins' secondary structure composition may be also determined using Fourier transform infrared (FT-IR) spectroscopy. In this method, structure elucidations are concluded from the shape of the amide I band, located around 1650-1660 cm À1 (Kanakis et al, 2011;Al-Hanish et al, 2016). Hydrogen bonding and the coupling between transition dipoles are the key factors that play a crucial role in governing the conformational sensitivity of the amide bands of proteins (Bose, 2016).…”

“…The peaks corresponding to b-sheet (1610-1637 cm À1 ), random coil (1638-1648 cm À1 ), ahelix (1649-1660 cm À1 ), b-turn (1660-1680 cm À1 ) and b-antiparallel sheet (1680-1692 cm À1 ) should be measured, and the area is determined with the Gaussian function. The area of individual band assigned to a given secondary structure should be then divided by the total area (Kanakis et al, 2011;Al-Hanish et al, 2016). Using FT-IR spectroscopy to investigate tea polyphenol-b-lactoglobulin interaction (pH 7.4), a major increase in b-sheet and a minor increase in ahelix was observed (Kanakis et al, 2011).…”

“…The thermodynamic (thermochemical) properties of the binding interaction between phenolic compounds and proteins may be investigated by isothermal titration calorimetry (ITC). The method is based on the measurement of the heat evolved during molecular association (Vesic et al, 2015;Al-Hanish et al, 2016). Thermodynamic parameters (free energy changes (DG), enthalpy changes (DH) and entropy changes (DS)) of interactions are essential to interpret the binding mode.…”

“…The positive enthalpy and entropy changes show that hydrophobic forces play a major role in the binding (Bose, 2016). Thanks to isothermal titration calorimetry, Al-Hanish et al (2016) demonstrated that the formation of a-lactalbumin and epigalocatechin-3-gallate (ECGC) complex results in typical exothermic enthalpy change (20 mM phosphate buffer, pH 7.2). Such phenomenon was also observed upon binding of ECGC to lipase (Wu et al, 2013), BSA, b-casein and porcine gelatin (Bohin et al, 2012), ovalbumin (Ognjenovic et al, 2014), insulin (Wang et al, 2012), keratin (Zhao et al, 2013), catalase (Pal et al, 2014) and Ara h 2 and Ara h 6 proteins (Vesic et al, 2015).…”