REGULATION OF RECEPTOR-BINDING AFFINITY OF INFLUENZA-VIRUS HEMAGGLUTININ BY ITS CARBOHYDRATE MOIETY

The hemagglutinin (HA) of the fowl plague virus (FPV) strain of influe nza A virus has two N-linked oligosaccharides attached to Asn123 and A sn149 in the vicinity of the receptor binding site. The effect of thes e carbohydrate side chains on the binding of HA to neuraminic acid-con taining receptors has been analyzed. When the oligosaccharides were de leted by site-specific mutagenesis, HA expressed from a simian virus 4 0 vector showed enhanced hemadsorbing activity. Binding was so strong under these conditions that erythrocytes were no longer released by vi ral neuraminidase and that release was significantly reduced when neur aminidase from Vibrio cholerae was used. Similarly, when these oligosa ccharides were removed selectively from purified viruses by N-glycosid ase F, such virions were unable to elute from receptors, although they retained neuraminidase activity. Thus, release of FPV from cell recep tors depends on the presence of the HA glycans at Asn123 and Asn149. O n the other hand, receptor binding was abolished when these oligosacch arides were sialylated after expression in the absence of neuraminidas e (M. Ohuchi, A. Feldmann, R. Ohuchi, and H.-D. Klenk, Virology 212:77 -83, 1995). These observations indicate that the receptor affinity of FPV HA is controlled by oligosaccharides adjacent to the receptor bind ing site.