抄録
Staphylococcal enterotoxin A (SEA) is a toxic protein and is the most common cause of staphylococcal food poisoning. In our previous studies, we identified some polyphenols that inhibited SEA toxin activities. In the present study, we investigated the interaction between four catechins (EC, ECG, EGC and EGCG) and SEA and the inhibitory effects of catechins on SEA activity. The interactions of catechins with SEA toxin active sites were analyzed using 4 different synthetic peptides and rabbit antibodies to their corresponding peptides (A-2, A-3, A-6 and A-10). As a result, EGCG inhibited the binding affinity of the all anti-peptides. When we examined whether EGCG inhibits cell proliferation and interferon-γ (IFN-γ) production induced by SEA in mouse spleen cells, we found that EGCG strongly inactivated cell proliferation and IFN-γ production induced by SEA. We examined changes in binding affinity of EGCG under digestive tract conditions by treatment under acidic or alkaline pH (pH2.4-8.0) with or without protein (bovine serum albumin). Results showed EGCG maintained binding affinity to SEA. We further investigated the binding of catechins to SEA using surface plasmon resonance (Biacore), isothermal titration calorimetry and protein-ligand docking. According to thermodynamic parameters, a negative ΔG indicated that the interaction between EGCG and SEA was spontaneous, and the electrostatic force accompanied by hydrophobic binding forces may play a major role in the binding. Data from Western blot analysis and docking simulation suggest that the hydroxyl group at position 3 of the galloyl group in the catechin structure was responsible for binding affinity with the Y91 of the A-6 region in SEA active sites. Our results provide further understanding of the binding interactions between catechins and SEA, and the inhibition of toxin activities by catechins.
