Induction of gp41 six-helix bundles by HIV-1 treatment with sCD4, CAP, CCR5 S-peptide and heat. HIV-1 IIIB and HIV-1 BaL, respectively, were treated with CAP and sCD4 as described in the legend for Fig. 5 or exposed to 60°C for 10 min. HIV-1 BaL was also treated with the S-peptide and a control non-sulfated peptide from CCR5 as described in the legend for Fig. 7. The treated virus preparations and untreated control virus were treated with lysis buffer (see Methods) for 30 min at 20°C. CAP in lysis buffer (0.078 to 10 mg/ml) was also tested; the results for a 5 mg/ml concentration are shown (identical results were obtained for all other concentrations). The lysates were tested by a sandwich ELISA for the gp41 six-helix bundle (see Methods). All experiments were done at least in triplicate.