SIALIDASE OF SWINE INFLUENZA-A VIRUSES - VARIATION OF THE RECOGNITIONSPECIFICITIES FOR SIALYL LINKAGES AND FOR THE MOLECULAR-SPECIES OF SIALIC-ACID WITH THE YEAR OF ISOLATION

The sialidase of swine influenza A viruses of N1 and N2 subtypes, isol ated from 1930 to 1992, was studied for substrate specificity with gan glio-series, lacto-series type II and GM3 gangliosides containing Neu5 Ac alpha 2-3Gal, Neu5Gc alpha 2-3Gal and Neu5Ac alpha 2-6Gal linkages. All viral sialidases tested showed that the activity for hydrolysing substrates with Neu5Ac alpha 2-3Gal was higher than the activities wit h Neu5Gc alpha 2-3Gal and Neu5Ac alpha 2-6Gal linkages. When GM1b, GM3 and sialylparagloboside were used as substrates, the earliest strain (A/Wisconsin/15/30 H1N1, isolated in 1930) showed the activity ratio o f Neu5Ac alpha 2-6Gal to Neu5Ac alpha 2-3Gal to be 0.13:0.2, and the r atio Neu5Gc alpha 2-3Gal/Neu5Ac alpha 2-3Gal to be 0.19:0.37, while th ose strains isolated from 1978 to 1992 exhibited ratios of 0.29:0.58 f or Neu5Ac alpha 2-6Gal/Neu5Ac alpha 2-3Gal and 0.51:0.76 for Neu5Gc al pha 2-3Gal/Neu5Ac alpha 2-3Gal. The above results indicate that the su bstrate specificities of sialidases from swine influenza A viruses tow ards sialyl linkages and the molecular species of sialic acid are rela ted to the year of isolation, i.e. strains isolated after 1978 exhibit ed higher activity towards Neu5Ac alpha 2-6Gal and Neu5Gc alpha 2-3Gal linkages when compared with strains isolated in an earlier year, 1930 .