Study on the interaction of flavonoids with proteins Presentation for thesis
Introduction 1 . Dietary f lavonoids are the important polyphenolic compounds in many plant foods. Flavonoids from dietary sources have attracted interest for their nutritional and medical effects on human health.
The different structures of flavonoids also strongly affect the binding process with proteins in blood. The interaction between serum albumin and flavonoids has attracted great interest among researchers because it can provide important information for nutritional and clinical research. However, the influence of the number and distribution of the hydroxyl groups and their substitutions in rings A and B of flavonoids on binding to serum albumin is not understood.
Flavonoids have many bio-activities, such as anti-oxidant, anti-tumoral, and anti-inflammatory. Many bio- activities are attributed to the antioxidant property, which was decided by the structure. The presence of hydroxyl groups on the ring B, and the presence of C-5 and C-7 hydroxyl groups on the ring A are required for anti-oxidant activity. The different structures of flavonoids affect the absorption, and metabolism in vivo.
Objective The work in this thesis mainly concerns about the influence of the number of the hydroxyl groups and their glycosylation of flavonids on binding with BSA and application of the binding affinity .
BSA Flavonoid Mix Incubate 37 °C spectrofluorometer
Outline 1. Interaction between flavonoids and BSA a) Effect of the number of OH groups on the ring B of flavonols on binding with BSA. b) Effect of the glycosylation of flavonoids on binding with BSA. 2. Effect of EGCG on the inhibitory activity of huperzine A, an acetylcholinesterase inhibitor.
1. Influence of hydroxylation in ring B of flavonol on interaction with BSA Galangin Kaempferol Quercetin Myricetin
Fluorescence spectra Kaempferol : 0, 2.... 20×10 -7 M Quercetin : 0, 2.... 20×10 -7 M
Relationship of binding constants (lgK a ) with the number of hydroxyl group on ring B
Relationship of binding sites (n) with the number of hydroxyl group on the ring B
Relationship of binding constant (lgK a ) with partition coefficient (K ow ) of flavonols. The partition coefficients were from Moreira et al. Life Sci., 2007, 81, 317-26
Relationship of chromatographic retention factor (K ʹ ) and binding constant (lgK a ) of flavonols
Highly electronegative surface areas for flavonol.
Result The binding constants ( K a ) and the binding sites (n) between flavonols and BSA increase with the increased number of hydroxyl groups on the ring B of flavonols . The hydrogen bond force is found to play an important role in binding flavonols to BSA
2. Influence of glycosylation of flavonoid interaction with BSA Genistein Daidzein Genistin Daidzin Baicalein Baicalin Quercitrin Quercetin
Quercetin : 0, 2.... 20×10 -7 M Quercitrin : 0,1,2...10×10 -6 M BSA Fluorescence quenching by flavonoids
Genistein : 0, 1.... 10×10 -6 M Genistein : 0, 1.... 10×10 -6 M Genistin : 0,0.25,0.5...2.5×10 -5 M
Glycosidation lower the affinities to serum albumin by 1-3 order of magnitude
Result The binding constants between flavonoids and BSA decrease after glycosylation. After OH was substituted by glycoside, the steric hindrance may take place, which weakens the binding affinity.
Relationship between the binding constants (K a ) and the binding sites (n) between flavonoids and BSA
Relationship of binding constant and half-wave potential of flavonol The E 1/2 values were from Yang et al. Anal Sci., 2001, 17, 599-604
3. Investigation the mechanism of enhanced effect of EGCG on huperzine A inhibiting acetylcholinesterase activity huperzine A EGCG
The combined effect of EGCG and huperzine A on AChE activity ( Zhang et al., 2006 )
The inhibitory effect of huperzine A on AChE activity was quite weak in the whole phase. Upon addition of EGCG to the huperzine A, the remarkably enhanced inhibitory effect on AChE activity were observed. The EGCG also can largely prolong the inhibitory time.
The quenching effect of Hup A on BSA under 2.00 × 10 -7 mol l -1 of EGCG
Synchronous fluorescence spectra of interaction between BSA-EGCG complex with Hup A at Δλ=15 nm. [EGCG]= 4 × 10 -7 M [BSA]= 1 × 10 -6 M [Hup A] a-h, 0, 0.5, 1.0 ... 3.5 × 10 -6 M
Interaction between EGCG-BSA complex with Hup A
Result 1. A very strong binding force forms between EGCG and BSA. (2.96 × 10 7 l mol -1 ). 2. HUP hardly interacts with BSA. 3. EGCG enhances Hup A interaction with BSA. 4. HUP interacts with EGCG-BSA complex, which enhances the transport capacity of HUP in blood.
Conclusion The number of the hydroxyl groups and their glycosylation in flavonoids affect binding process. For flavonols, the binding constant increases with increased number of hydroxyl groups on the ring B. For flavonoids, t he binding constant decreases after glycosylation . The binding site increases with the increased binding constant.