FU Qiaoqin, ZHANG Lu, JIA Xiaoyan, MA Tianxin, TU Zongcai
Flavonoids are the major bioactive compounds of many plant foods, the interaction with proteins can affect its transport and metabolism in human body. To evaluate the influence of 3-OH glycosylated substitution on the interaction of quercetin with human serum albumin (HSA), five common flavonols, quercetin-3-O-rhamnoside (Q3Rh), quercetin (Que), quercetin-3-O-xyloside (Q3X), quercetin-3-O-rutinoside (Q3Ru), and quercetin-3-O-glucoside (Q3G) were tested by fluorescence spectroscopy and molecular docking techniques. The results indicated that five tested flavonols all quenched the fluorescence of HSA via a static mechanism, stable complexes were formed via a spontaneously exothermic process. Glycosylated substitution on 3-OH decreased the fluorescence quenching efficacy of quercetin on HSA, as well as its binding ability. Q3Ru and Q3X exhibited the weakest fluorescence quenching ability, while Q3G showed the lowest binding ability. Synchronous fluorescence analysis revealed that Que, Q3Ru, Q3X, Q3G, and Q3Rh increased the polarity in the micro-environment of tryptophan, but did not alter the polarity in the vicinity of tyrosine residue. Glycosylation on 3-OH enhanced the impact on tryptophan micro-environment, glucose exhibited the strongest role. Thermodynamics and molecular docking results indicated that Que, Q3X, Q3Rh, Q3G and Q3Ru inserted into the hydrophobic cavity of HSA through hydrophobic interactions, hydrogen bonds, and van der Waals forces, and 4, 6, 5, 2 and 4 hydrogen bonds were formed accordingly. Glycosylated substitution would not obviously change the binding region and interaction forces of quercetin with HSA, but could alter the amino acids involved in the formation of complexes. The results could help to explain the different interaction mechanism of food nutrition with different glycosylated substitutions, as well as their transport and metabolism in vitro. And it also provides a certain theoretical foundation for its structure-bioactivity relationship analysis.
