Study Of The Mechanism By Which Tannin Inhibits HIV-1 Fusion With Target Cells And Screening Compounds From Actinomycetes For HIV-1 Fusion Inhibitors Targeting Gp41

HIV-1 gp41, a transmemberane subunit of the envelope glycoprotein, plays an important role in the early steps of virus entry into target cells. It is essential to develop new anti-HIV agents with gp41 as a target. The N- and C-terminal heptad repeat (designated NHR and CHR, respectively) regions of gp41 extracellular domain can form a six-helix bundle by interaction, which brings both the viral and target cell membranes into proximity for fusion. Similarly, any compound that interacts with the gp41 NHR region may also block the six-helix bundle formation and inhibit HIV-1 entry into target cells. Using a monoclonal antibody (NC-1) specific for the gp41 six-helix bundle, Doctor Jiang shi-bo previously developed a sandwich enzyme-linked immunosorbent assay (ELISA) to screen for HIV-1 entry inhibitors targeting gp41 .Extracts of several Chinese medicinal herbs have been shown to have anti-HIV-1 activity, which is correlated with the concentrations of polyphenolic compounds in the extracts. Our previous study has demonstrated that the polyphenolic compounds isolated from two antiviral herbs interact with the peptides derived from the HIV-1 gp41, suggesting thatthe active components in these herbs may inhibit HIV-1 entry by targeting gp41. Tannin (also named tannic acid) is a polyphenolic compound with a potent anti-HIV-1 activity. It is interesting to know whether tannin also inhibits HIV-1 entry into target cells and what is the mechanism of action. The inhibitory activity of tannin on HIV-1 infectivity was detected by p24 production and HIV-1-mediated cell fusion and that on the gp41 six-helix bundle formation was determined by a modified sandwich ELISA. Using the approach in the present study, we demonstrated that tannin inhibited not only HIV-1 replication, but also HIV-1 entry. Study of the action mechanism indicated that tannin blocked the gp41 six-helix bundle formation, thus inhibiting HIV-1 fusion with the target cell membrane.In the present study, we use the sandwich ELISA to screen products from 985 actinomycetes fermentations, in order to identify the active components that may disrupt the HIV-1 gp41 six-helix bundle formation. Among them, 83 actinomyces fermentation products can potently inhibit the gp41 six-helix bundle formation. Six samples could inhibit the cell fusion and HIV-1 induced cytopathic effect (CPE), and the sample of strain NO.25-04, identified as streptomyces hygroscopicus, was the strongest. We optimized a culture medium formula to increase the activity in the fermentation products and a kind of polysaccharide, isolated and purified from strain NO.25-04, was confirmed to be responsible for the inhibitory activity on HIV-1 gp41 six-helix bundle formation. The MW of the compound is about 3,0000-7,0000.