FIG. 4.

Conversion of RBD mutants to an active conformation. Liposome flotation assays were performed on wild-type (wt) and RBD mutant EnvA PI proteins in the presence (+) or absence (−) of excess sTva. EnvA PI, with and without sTva, and liposomes were incubated at 37°C for 15 min before ultracentrifugation. The fractions were collected, acid precipitated, and analyzed by Western blotting with antiserum against SU detected by ECL, as described in Materials and Methods. B, M, and T denote the bottom, middle, and top fractions, respectively. Greater that 90% of the liposomes recovered are within the top fraction (data not shown).