Binding of Catechins to Staphylococcal Enterotoxin A

Abstract

Staphylococcal enterotoxin A (SEA) is a toxin protein, and is the most common cause of staphylococcal food poisoning. Polyphenols, such as catechins, are known to interact with proteins. In this study, we investigated the binding of catechins to SEA using SPR (Biacore), Fourier transform infrared spectroscopy (FT-IR), isothermal titration calorimetry (ITC), and protein-ligand docking. We found that (−)-epigallocatechin gallate (EGCG) could strongly bind to SEA. 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 of SEA active sites. Our results provide further understanding of the binding interactions between catechins and SEA, and the inhibition of toxin activities by catechins.

Effect of (−)-Epigallocatechin Gallate to Staphylococcal Enterotoxin A on Toxin Activity

“…Therefore, whether the binding between EGCG and SEA was the essential factor for inhibiting the cytotoxicity of SEA was examined. Previous studies have shown that EGCG and (−)-4-Me-EGCG interact with SEA, and (−)-3 -Me-EGCG does not interact with SEA [18]. The only difference between EGCG and (−)-3 -Me-EGCG is the presence of a methyl group at the 3 -position of the galloyl group (Figure 4a).…”

“…The strength of interaction between human serum albumin (HSA) having high homology to BSA and EGCG or a methylated EGCG was in the order of (−)-3 -Me-EGCG > (−)-4 -Me-EGCG > EGCG [26]. In previous studies, the strength of interaction between SEA and EGCG or a methylated EGCG was in the order of EGCG ≥ (−)-4 -Me-EGCG > (−)-3 -Me-EGCG [18]. The flavan-3-ol and the galloyl group of EGCG are essential for site-specific, high-affinity binding for serum albumin [27].…”

“…SEA activates large numbers of T cells by cross-linking MHC class II and TCR, resulting in excessive cytokine production [10][11][12]. We previously reported that EGCG binds to SEA [18], therefore, it was thought that EGCG may have the ability to inhibit MHC class II binding to SEA. However, changes in SEA toxin activity due to the binding of SEA to EGCG have not been clarified.…”

“…Rasooly et al (2010) reported that superantigen activity of SEA can be evaluated using mouse spleen cells [18]. The CD4 + T cell responses can be generally divided into two distinct types based on cytokine expression, designated Th1 and Th2 [19].…”

“…A detailed understanding of the molecular properties of catechins may lead to their application in medicine and food chemistry. We previously reported that EGCG binds to SEA [18], indicating that EGCG may have the ability to inhibit MHC class II binding to SEA. However, changes in SEA toxin activity due to the binding of SEA to EGCG have not been clarified.…”