Antiviral activity and structural characteristics of the nonglycosylated central subdomain of human respiratory syncytial virus attachment (G) glycoprotein

Segments of the cystine noose-containing nonglycosylated central subdomain, residues 149-197, of the attachment (G) glycoprotein of human respiratory syncytial virus (HRSV) have been assessed for impact on the cytopathic effe ct (CPE) of respiratory syncytial virus (RSV). N alpha -acetyl residues 149 -197-amide (G149-197), 6149-189, and 6149-177 of the A2 strain of HRSV prot ected 50% of human epithelial HEp-2 cells from the CPE of the A2 strain at concentrations (IC50) between 5 and 80 muM. Cystine noose-containing peptid es G171-197 and G173-197 did not inhibit the CPE even at concentrations abo ve 150 muM. Systematic C- and N-terminal truncations from 6149-189 and 6149 -177 and alanine substitutions within G154-177 demonstrated that residues 1 66-170 (EVFNF), within a sequence that is conserved in HRSV strains, were c ritical for inhibition. Concordantly, G154-177 of bovine RSV and of an anti body escape mutant of HRSV with residues 166-170 of QTLPY and EVSNP, respec tively, were not inhibitory. Surprisingly, a variant of G154-177 with an E1 66A substitution had an IC50 of 750 nm. NMR analysis demonstrated that G149 -177 adopted a well-defined conformation in solution, clustered around F168 and F170. G154-170, particularly EVFNF, may be important in binding of RSV to host cells. These findings constitute a promising platform for the deve lopment of antiviral agents for RSV.