Inactive precursor that is cleaved at two sites by a furin-like protease to give rise to the mature F1 and F2 fusion glycoproteins. Class I viral fusion protein. Under the current model, the protein has at least 3 conformational states: pre-fusion native state, pre-hairpin intermediate state, and post-fusion hairpin state. During viral and plasma cell membrane fusion, the coiled coil regions assume a trimer-of-hairpins structure, positioning the fusion peptide in close proximity to the C-terminal region of the ectodomain. The formation of this structure appears to drive apposition and subsequent fusion of viral and cellular membranes leading to delivery of the nucleocapsid into the cytoplasm. This fusion is pH independent and occurs at the plasma or endosomal membrane. The trimer of F1-F2 (F protein) also facilitates the attachment and entry into the host cell. Later in infection, F protein expressed at the plasma membrane of infected cells can mediate fusion with adjacent cells to form syncytia, a cytopathic effect that could lead to tissue necrosis. Major determinant of the species specificity of RSV infection. The trimer of F1-F2 (F protein) also facilitates the attachment and entry into the host cell. Later in infection, F protein expressed at the plasma membrane of infected cells can mediate fusion with adjacent cells to form syncytia, a cytopathic effect that could lead to tissue necrosis. Homotrimer. Heterodimer with fusion protein F2; disulfide-linked. Part of a complex composed of F1, F2 and G glycoproteins. As a heterodimer with F2, interacts with host RHOA; this interaction facilitates virus-induced syncytium formation. Homotrimer. Heterodimer with fusion protein F1; disulfide-linked. Part of a complex composed of F1, F2 and G glycoproteins. As a heterodimer with F1, interacts with host RHOA; this interaction facilitates virus-induced syncytium formation. Localized at the host apical membrane. Localized at the host apical membrane. The N-terminus is a hydrophobic fusion peptide that inserts into the target host membrane (By similarity). It is buried in the center of the trimer cavity before cleavage by host furin. The coiled coil (heptad repeat) regions are probably involved in homotrimerization, heterodimerization and in the formation of a fusion-active hairpin structure (By similarity). The N-terminus is a hydrophobic fusion peptide that inserts into the target host membrane (By similarity). It is buried in the center of the trimer cavity before cleavage by host furin. The coiled coil (heptad repeat) regions are probably involved in homotrimerization, heterodimerization and in the formation of a fusion-active hairpin structure (By similarity). The F glycoprotein is synthesized as a F0 inactive precursor that is heavily N-glycosylated and processed at two sites by a host furin-like protease probably in the Golgi. The cleavage site between p27 and F1 may occur after endocytosis to yield the mature F1 and F2 proteins. Both cleavages are required for membrane fusion and p27 is released from the processed protein. Belongs to the paramyxoviruses fusion glycoprotein family. Ser-550 is present instead of the conserved Cys which is expected to bind palmitate.