Interaction of the transactivating protein HIV-1 tat with sulphated polysaccharides

Endogenous sulphated polysaccharides such as heparin have been shown to inhibit the infectivity of HIV-I in vitro. However, these naturally occurring polymers, due to extensive microheterogeneity within their structure, are difficult to characterise accurately. In contrast, dextrin can be chemically sulphated to produce a series of compounds sulphated in the 2-, 3-, or 6- position, or in all 3 positions, and the use of these compounds provides an opportunity to investigate the anti-HIV-l activity of sulphated polysaccharides. The mechanisms whereby sulphated polysaccharides exert their anti-HIV-l activity have not been fully elucidated. The interaction of recombinant HIV-1 proteins with sulphated polysaccharides was investigated using a biotinylated derivative of dextrin 2-sulphate (D2S) in a solid phase binding system. D2S was found to bind strongly to HIV-I rat (EC50 = 0.10 mu g/mL), less strongly to CD4 (EC50 = 0.33 mu g/mL), weakly to HIV-I vif and gp160, and not at all to HIV-1 gp120 or p24. Other sulphated derivatives of dextrin, i.e. dextrin 3-sulphate, dextrin 6-sulphate and dextrin 2,3,6-trisulphate, as well as heparin and dextran sulphate, were also shown to bind to HIV-I tar, whereas the unsulphated compound dextrin did not. Binding studies using a series of overlapping peptides representing the complete sequence of HIV-1 rat revealed that D2S bound most strongly to the core domain of HIV-1 tar, although there was also binding to the cysteine-rich domain; both of these regions are important for HIV-1 rat function. In assessing function, HIV-1 rat-mediated transactivation was measured using H938 cells, a cell line that contains the HIV-LTR (long terminal repeat) promoter linked to a chloramphenicol acetyltransferase gene. D2S significantly inhibited HIV-1 rat transactivation in a dose-dependent manner (IC50 = 0.5 mu g/mL), whereas dextrin had no effect. The interaction between D2S and HIV-1 tar provides a potential mechanism of HIV-I inhibition whereby rat is sequestered and its transactivating activity abolished, effectively inhibiting the replication cycle. (C) 1999 Elsevier Science Inc.