Alternative conformations of a major antigenic site on RSV F

Jones, Harrison G.; Battles, Michael B.; Lin, Chun-Chi; Bianchi, Siro; Corti, Davide; McLellan, Jason S.

AM22 and RSD5 are two human antibodies that bind to antigenic site Ø and are specific for the prefusion conformation of RSV F. Although both antibodies potently neutralize RSV, similar to D25, their binding kinetics and subtype specificity have distinct differences. AM22 and D25 both preferentially bind to subtype A, whereas RSD5 preferentially binds to subtype B as a result of its fast dissociation rate constant for subtype A F proteins. In addition, previous publications using SPR and flow cytometry-based competition assays have suggested that AM22 and RSD5 do not compete with D25, but rather occupy a separate prefusion-specific epitope [37, 38] . However, comparing the crystal structures of prefusion RSV F bound to AM22, RSD5-GL, and D25, demonstrates that all three antibody epitopes overlap substantially and would prevent any two from binding simultaneously due to large steric clashes. This emphasizes the importance of structural characterization of antibody epitopes in addition to competition data, as varying antibody kinetics can mislead epitope classification when using only competition assays.