Homogeneity of the structural glycoprotein from European isolates of tick-borne encephalitis virus: comparison with other flaviviruses.

Isolates of tick-borne encephalitis (TBE) virus from Finland, Germany, Czechoslovakia, Switzerland and Austria were compared with strains of the Far Eastern subtype isolated in Russia as well as Louping ill virus and other flaviviruses belonging to a different serocomplex: West Nile, Murray Valley encephalitis and Rocio viruses. Analysis of the structural polypeptides by SDS--polyacrylamide gel electrophoresis (SDS--PAGE) revealed identical mol. wt. of the glycoprotein E (mol. wt. 55 000) and the core protein C (mol. wt. 15 000) for all the TBE virus strains analysed. However, the small envelope protein M from viruses isolated in Germany, Switzerland and Austria migrated slightly slower (apparent mol. wt. 7500) compared to M from viruses isolated in Finland, Czechoslovakia or the Far Eastern subtype strains (apparent mol. wt. 6500 to 7000). The structural glycoproteins were isolated from purified [35S]methionine-labeled virions and subjected to peptide mapping by limited proteolysis with alpha-chymotrypsin or V8 protease followed by SDS--PAGE of the resulting cleavage products. With both proteases a remarkably homogeneous pattern was obtained for all the European isolates with only very minor deviations from a common pattern in single cases. Similar but distinguishable patterns were obtained for the Far Eastern subtype strains and also Louping ill virus, which, in addition, differed in the mol. wt. of its core protein C (mol. wt. 16 000) and the small membrane protein M (mol. wt. 9000). These almost identical peptide maps observed with the TBE virus strains were in sharp contrast to the unrelated patterns obtained with the glycoproteins from West Nile, Murray Valley encephalitis and Rocio viruses. Although these viruses are serologically closely related and members of the same serocomplex of flaviviruses their glycoprotein peptide maps were completely different from one another. In a competitive radioimmunoassay all European TBE virus isolates showed identical immunological reactivity which further points to the great stability of this type of virus.