Further Studies on the Role of Neuraminidase and the Mechanism of Low pH Dependence in Influenza Virus-induced Membrane Fusion

Abstract

SUMMARYThe role of neuraminidase and the mechanism of low pH dependence in influenza virus-induced membrane fusion have been studied further using fowl plague virus (FPV, H7N 1). Two specific anti-FPV neuraminidase antisera obtained from chickens immunized with recombinant virus strains inhibited viral neuraminidase activity without influencing its haemagglutinating activity. These sera totally inhibited the FPV-induced fusion of erythrocytes and partially reduced haemolysis. But both fusion and haemolysis activities could be restored by external addition of Vibrio cholerae neuraminidase, indicating participation of neuraminidase in FPV-induced membrane fusion. With regard to low pH-dependent fusion by influenza virus, it was found that erythrocytes of various species showed different pH optima for haemolysis by FPV and that erythrocytes could be sensitized for fusion and haemolysis by FPV at neutral pH if they had been pretreated with a low pH buffer. These results demonstrated that surface properties of erythrocytes rather than that of the virus are critical in the low pHdependent fusion and haemolysis by influenza viruses.

PH-dependent Fusion between the Flavivirus West Nile and Liposomal Model Membranes

“…Similarly a recent study (Huang et al, 1985) has indicated a role for the target membrane in dictating the exact pH optimum for fusion of influenza virus with red blood cells.…”

Characterization of the receptor-destroying enzyme activity from infectious salmon anaemia virus

“…The enzyme has also been suggested to play a role in initiation of infection, either by promoting fusion activity (Huang et al, 1980(Huang et al, , 1985 or by releasing sialic acids from oligosaccharides that may interfere with the binding to cellular receptors near the receptor-binding site (Ohuchi et al, 1995). The HEF protein of influenza C virus is known to bind cellular receptors containing 9-O-acetyl-5-N-acetylsialic acids as the major receptor determinant and releases the acetyl residue from position C-9 of the substrate (Herrler & Klenk, 1987 ;Rogers et al, 1986).…”

Characterization of Sialidase from an Influenza A (H3N2) Virus Strain: Kinetic Parameters and Substrate Specificity

“…Sialidase is also involved in the breakdown of the mucosal lining of the upper respiratory tract during the initial infection and contributes to the release of the virion by the budding process [23,28]. This enzyme hydrolyses ·-O-ketoglycosidic linkages of terminal sialic acid residues on glycoconjugates of viral and cellular origin which would otherwise cause HA-mediated self-aggregation of the virus particles [17]. The spike NA is a 200-to 240-kD tetrameric structure, presenting a hydrophilic region with antigenic and catalytic sites and a hydrophobic one that is inserted into the virion lipid envelope [10].…”