PROBING THE STRUCTURE OF INFLUENZA-B HEMAGGLUTININ USING SITE-DIRECTED MUTAGENESIS

The crystal structure of the hemagglutinin (HA) of influenza virus A/A ichi/68 (H3N2) from the X-31 reassortant virus was reported in 1981, b ut as yet there are no X-ray diffraction structures for hemagglutinins of other types or even subtypes of influenza virus. We have used site -directed mutagenesis to probe the structure of the hemagglutinin of i nfluenza B/Hong Kong/8/73. we investigated a region in the globular he ad domain that is helical in the influenza A HA structure, targeting s idechains that in the H3 HA point toward solvent (Thr196) or into the receptor-binding pocket (Gln197). None of the mutations affected hemag glutination activity, but mutations T196P or Q1971 eliminated binding of a monoclonal antibody. The data suggest that this region of the inf luenza B HA forms a surface structure different from the alpha-helix o f the influenza A HA structure and that it accounts for much of the an tigenic activity of influenza B HA. (C) 1995 Academic Press, Inc.