Isolation of the influenza C virus glycoprotein in a soluble form by bromelain digestion

Fusion Characteristics of Influenza C Viruses

“…On the other hand, it could also be that a cooperative event; whiekwould lead to a sigmoid curve of fusion activity, is needed becausea change in more than one spike molecule is necessary to induce fusion as was proposed for the HA of influenza A virus (Doms et al, 1985;Blumenthal et al, 1989). This could also explain the observation that isolated glycoprotein showed no haemolysis of erythrocytes at low pH (Herrler et al, 1988;Formanowski & Meier-Ewert, 1988). For detergent-isolated HA of influenza A virus haemolysis and fusion at low pH could be demonstrated (Sato et al, 1983;Wharton et al, 1.986) and ex, en the bromelainreleased HA showed a reduced rate of haemolysis but no fusion activity .…”

“…Therefore, it was proposed that influenza C virus enters the cell via the endocytic pathway and subsequently fuses with the membrane of the endosome after its acidification (reviewed by White et al, 1983;Wharton, 1987). The glycoprotein undergoes a conformational change at low pH, which can be shown by the susceptibility of the low pH structure to trypsin digestion (Formanowski & Meier-Ewert, 1988). A similar conformational change of the HA of influenza A viruses has been described (Skehel et aL, 1982).…”

“…The following influenza C virus strains were used: C/Taylor/47 (C/TAY/47), C/Ann Arbor/I/50 (C/AA/1/50), C/Yamagata/64, C/Johannesburg/I/66 (C/JHB/I/66), C/Bavaria/79, C/Greece/79 and C/Kansas/79. Viruses were grown in 10-day-old embryonated chicken eggs or in MDCK I cells as described previously (Formanowski & Meier-Ewert, 1988). Uncleared glycoprotein of MDCK I cell-grown virions was cleaved in vitro with 10 gg/ml TPCKtreated trypsin (Sigma).…”

“…In addition the glycoprotein was found to possess a receptor-destroying enzyme activity (Vlasak et al, 1987;Herrler et al, 1988;Formanowski & Meier-Ewert, 1988). Therefore the name HEF has been proposed for the influenza C virus glycoprotein (Herrler et al, 1988) standing for haemagglutinin, esterase and fusion protein.…”

Construction of an antigenic map of the haemagglutinin-esterase protein of influenza C virus

“…The haemagglutinin-esterase (HE) glycoprotein of influenza C virus has three biological roles, receptor-binding, fusion with the host cell membrane and receptordestroying activity (Sugawara et al, 1985Vlasak et al, 1987;Herrler et al, 1988a;Formanowski & Meier-Ewert, 1988), the last of which has been identified as being carried out by a neuraminate-O-acetylesterase (Herder et al, 1985). The glycoprotein may be present in virions as two proteolytic cleavage products, HE1 and HE2, that are held together by disulphide bonding (Herrler et al, 1979).…”