Comparison of structure and sequence of influenza B/Yamagata and B/Beijing neuraminidases shows a conserved "head" but much greater variability in the "stalk" and NB protein.

In 1988 the B/Yamagata/16/88 influenza virus appeared, which was antigenically quite different from the other B viruses circulating at that time. Neuraminidase heads of this strain were purified, crystallized, and analyzed by X-ray crystallography and compared with the structure of B/Beijing/1/87 neuraminidase. Only two point mutations could be detected in the "head" of the molecule leading to local rearrangement of amino acid side-chains. The nucleotide sequence, however, revealed significant differences in the stalk region and in the NB protein.