Multiple heparin binding domains of respiratory syncytial virus G mediate binding to mammalian cells

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Abstract
Respiratory syncytial virus (RSV) G glycoprotein mediates cell attachment through surface glycosaminoglycans (GAGs). Feldman et al. [10] suggested that specific basic amino acids in residues 184–198 of G defined a critical heparin binding domain (HBD). To further define the G HBD we made a series of truncated G proteins expressed in Escherichia coli. G88 (G residues 143–231), bound to HEp-2 cells in a dose dependent manner and binding was inhibited >99% with heparin. Cell binding of G88 was unaltered by alanine substitution mutagenesis of all basic amino acids in Feldman’s region 184–198. A G88 variant truncated beyond residue 198, G58, and G58 fully alanine substituted in the region 184–198, G58A6, bound to HEp-2 cells about half as well and 100-fold less well than G88, respectively. G88 and all alanine substitution mutants of G88 inhibited RSV plaque formation by 50% (ID50) at concentrations of ∼50 nM; the ID50 of G58 was ∼425 nM while G58A6 had an ID50 >1600 nM. These data show that the G HBD includes as much as residues 187–231, that there is redundancy beyond the previously described HBD, and that the cell-binding and virus infectivity-blocking functions of these recombinant G proteins were closely linked and required at least one HBD.

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