Respiratory syncytial virus fusion protein (RSV F) antigenic site II (RSV F site II)

The Respiratory syncytial virus (RSV) fusion (F) protein antigenic site II is a critical neutralizing epitope located on the RSV F glycoprotein, which is essential for viral entry into host cells [1, 2]. This site consists of a helix-loop-helix motif (residues 255-275) and is notably conserved across both the metastable prefusion and stable postfusion conformations of the F protein [3, 11]. It is the primary target for palivizumab, a humanized monoclonal antibody used prophylactically to prevent severe lower respiratory tract infections, such as bronchiolitis and pneumonia, in high-risk infants [1, 12]. Binding of antibodies to site II neutralizes the virus by inhibiting the conformational changes required for membrane fusion, effectively blocking the delivery of the viral genome into the host cytoplasm [5, 11]. Despite its clinical success, therapeutic challenges include the emergence of viral resistance through mutations at key residues like Lys272 and the high cost of treatment [2, 12]. Recent research has also shifted focus toward more potent prefusion-specific epitopes, such as site Ø, for next-generation vaccines and antibodies [3, 14].

Other names

Site IIAntigenic site APalivizumab epitopeFsII

Neutralization of the virus by blocking the fusion process; binding to site II prevents the conformational change of the F protein from pre-fusion to post-fusion state.