*4.4.2 Attachment glycoprotein (G)*

In RSV-infected cells, G protein can exist in two forms; one is a membrane-bound form responsible for viral attachment and another is a secreted isoform responsible for immune evasion [53, 54]. The membrane-bound form (298 amino acids) is a type 2 integral membrane protein [55]. G protein has an amino-terminal cytoplasmic domain and a hydrophobic transmembrane domain; moreover, its ectodomain which undergoes post-translational modification with 4–5 N-linked glycans and 30–40 O-linked glycans, has two mucin-like regions and heparin-binding domains [55–57]. The translation of secreted G protein starts at an alternative AUG (Met48) located in the transmembrane domain allowing the ectodomain to secrete from the cell [58]. Both membrane-bound and secreted forms of G proteins are thought to be involved in RSV pathogenesis [59]. The higher variation of the mucin-like domain caused two subtypes of RSV: RSV A and RSV B [60].
