Protease treatment and chemical crosslinking of a Flavivirus: Tick borne encephalitis virus

Abstract

Summary Tick-borne encephalitis virus was treated with pronase or thermolysin. The resulting particles were banded in sucrose gradients and analyzed for polypeptide composition. Both enzymes caused a reduction in particle density from 1.19 to 1.15–1.16 g/cm³. No loss of viral lipid or nucleic acid could be observed. SDS-polyacrylamidegel electrophoresis showed that only the core protein V₂ was unchanged whereas the envelope proteins V₃ and V₁ had disappeared from their original positions in the PAGE profile. Instead a new peptide(s) with molecular weight of 4000–6000 was found in which hydrophobic amino-acids were enriched. Crosslinking by dimethyl-3.3′-dithiobispropionimidate (DTBP) made the virus resistent to solubilization of the envelope proteins by TX-100. This could be interpreted by the formation of a dense envelope protein network around the nucleocapsid preventing its liberation by TX-100. Some data however indicate that direct crosslinking of at least one of the envelope proteins with the core cannot be excluded.