Epigallocatechin gallate, the main polyphenol in green tea, binds to the T-cell receptor, CD4: Potential for HIV-1 therapy

The structure of (-)-catechin and EGCG. The rings are labeled.

Transfer of saturation in NMR. Saturation of the protein by a radio frequency pulse (red) is transferred around the protein (pink) and onto the bound ligand. Exchange permits the saturation to be visible on the free ligand, thus identifying that the ligand binds and characterizing its binding site.

Loss of intensity of EGCG signals on titration with CD4. The spectra on the left show signals from rings D and B of EGCG (at 6.92 and 6.55 ppm respectively), with addition of CD4 domain (from bottom to top). The signal marked with an asterisk is a low-molecular-weight compound present in the CD4 buffer. The EGCG signals decrease in intensity on addition of CD4, without any noticeable increase in line width. The graph on the right shows the approximately linear loss in intensity with increasing CD4 concentration.

Saturation transfer difference spectra. A, NMR spectrum of 310 μmol/L EGCG in the presence of 1.45 μmol/L PRO 542 (5.8 μmol/L CD4). The signals marked with asterisks are from low-molecular-weight compounds present in the CD4 buffer. B, STD spectrum from this solution. The intensities of the STDs at rings D, B, and A are 10%, 7.4%, and 10%, respectively. C, NMR spectrum of 310 μmol/L EGCG plus 310 μmol/L (-)-catechin in the presence of 1.45 μmol/L PRO 542 (5.8 μmol/L CD4). The catechin signals are marked c. D, STD spectrum from this solution. The intensities of the STDs at rings D, B, and A of EGCG are 9%, 6%, and 9%, respectively, whereas the STDs from catechin are in the range 1.5% to 3%. In B and D, there are no measurable STDs to the other signals marked with asterisks.

A model of EGCG binding to the D1 domain of CD4. Model drawn using PyMol, with the crystal structure coordinates 1CDJ.²² In the protein, carbon is yellow, oxygen is red, and nitrogen is purple. The view is approximately from the direction of binding of gp120.

EGCG inhibition of gp120 binding to human CD4⁺ T cells as assessed by flow cytometry. The data are expressed as means ± SDs of 6 independent experiments. Only significant differences are noted.