Nance C, Williamson M, Paulson S, McCormick T, Shearer W.

Epigallocatechin gallate, green tea catechin, binds to T cell receptor, CD4.

Texas Children's Hospital and Baylor College of Medicine, 6621 Fannin, MC: FC330.01, Houston, TX 77030. clnance@texaschildrenshospital.org

BACKGROUND: HIV-1 infection ultimately results in impaired immune function by virtue of the initial binding of the HIV envelope glycoprotein, gp120, to the CD4 receptor. The green tea flavonoid, epigallocatechin gallate (EGCG), has been proposed to have medicinal properties including anti-HIV effects. We sought to demonstrate that EGCG binds to the CD4 molecule at the gp120 attachment site and inhibits gp120 binding at physiologically relevant levels, thus establishing the potential use of EGCG as a therapeutic treatment for HIV infection.

METHODS: Saturation transfer difference-nuclear magnetic resonance (STD-NMR) spectroscopy experiments examined the binding of EGCG to CD4 utilizing the CD4-IgG fusion protein, PRO 542®. CD4+T cells were positively selected by immunomagnetic separation from platelet-depleted human leukopaks to obtain a highly purified CD4+Tcell population. Inhibition binding studies were assessed by flow cytometry.

RESULTS: In STD-NMR experiments, addition of CD4 to 100 mM EGCG voided the NMR signal from EGCG but not from the control, (-)-catechin. Addition of 21 µM CD4/binding site to 520 mM EGCG showed strong saturation at rings B and D of EGCG. On addition of a two-fold excess of (-)-catechin over EGCG, there is some reduction in signal intensity, but the only STD effects visible were to EGCG. To investigate whether the binding of EGCG to the CD4 molecule on human lymphocytes is capable of inhibiting the binding of gp120 to CD4, we analyzed the binding ability of gp120 to EGCG-treated and untreated CD4+T cells. EGCG markedly inhibited the binding of gp120 to CD4+ T cells in a dose-dependent manner (42% at 0.2µM, p=0.02; 47% at 2µM, p=0.006; and 55% at 20µM, p=0.001). Thus, at the physiologically relevant level of 0.2µM, EGCG exerted an inhibitory effect. The control catechin did not alter the binding capacity of gp120. Molecular modeling studies suggested a binding site for EGCG (Phe 43, Arg 59, Trp 62) in the D1 domain of CD4, the pocket that binds gp120.

CONCLUSIONS: We have demonstrated clear evidence of high affinity binding of EGCG to the CD4 molecule. EGCG at concentrations equivalent to those obtainable by the consumption of green tea is able to significantly reduce the attachment of gp120 to CD4. The competitive binding properties of EGCG for the CD4 binding sites by gp120 may translate to an HIV-1 preventative strategy. EGCG may have a potential use as adjunctive therapy in HIV infection.

 

Back