Neuraminidase and hemagglutinin activities in subcellular fractions of NDV- and FPV-infected chick embryo cells and their re-distribution following Triton X 100 treatment

Dynamics of functional maturation and inactivation of HN glycoprotein in NDV-infected chick embryo fibroblasts

In avirulent NDV strain-infected chick embryo cells treated with cycloheximide at different intervals post infection a decrease of the level of hemagglutinating (HA) and neuraminidase (Nase) activities was observed. Studies on this system led to conclusion that the HA-Nase (HN) glycoprotein molecules are unstable and the actual amount of the functionally active (mature) HN entities is determined by a dynamic equilibrium between the antidromic processes of the HN functional maturation and inactivation. Kinetic studies on the actual intracellular levels of the HA and Nase activities using 5 min intervals of their detection after the cycloheximide treatment permitted to uncouple the processes of the HN maturation and inactivation. Analytical part of the studies made it possible to compute quantitative parameters of the involved processes: (a) pool size of the functionally nonactive HN precursors, (b) time needed for their functional maturation, and (c) rate of their inactivation.

Effect of inhibitors of proteases and glycosidases on functional lability of newly synthesized hemagglutinin-neuraminidase glycoprotein in avirulent NDV strain-infected cells

Inhibition of either glycosylation or the protein synthesis leads to sharp drop of hemagglutinating (HA) and neuraminidase (Nase) activities in Newcastle disease virus (NDV)-infected cells. The drop can be prevented by tosyl-lysyl-chloromethyl-ketone, an inhibitor of trypsin-like proteases, or D-galactonolactone, an inhibitor of glycosidases, if added together with cycloheximide. Tosyl-lysyl-chloromethyl-ketone when added alone increases the level of both the HA and Nase activities as compared with non-treated virus-infected cells. It has been suggested that the actual level of the HA and Nase activities in the virus-infected cells is a result of dynamic equilibrium between the synthesis and post-translational functional maturation of the hemagglutinin-neuraminidase (HN) molecules, on the one hand, and the protease and glycosidase-mediated functional inactivation, on the other.

Antigenic relationships between avian paramyxoviruses. I. Quantitative characteristics based on hemagglutination and neuraminidase inhibition tests

Comprehensive hemagglutination inhibition (HI) and neuraminidase inhibition (NI) cross reaction tests were performed using 8 of 9 serotypes of avian paramyxoviruses (PMV). The studies were designed as full scale repeating experiments which permitted an adequate statistical treatment and elaboration of quantitative criteria of antigenic kinship. The results have shown diverse antigenic relationships between different avian paramyxovirus (PMV) serotypes which were asymmetric in some cases. The antigenic relationships found by HI test did not always parallel those found by NI tests. The antigenic inter-relationships have been displayed quantitatively in a diagram. This has given a basis for some suggestions concerning: the independent antigenic drift of the HA and Nase antigenic sites of hemagglutinin-neuraminidase (HN) glycoprotein of avian PMVs; a tentative subdivision of the whole group of avian PMVs into two subgroups: the first including PMV-2 and PMV-6 serotypes and the second including PMV-1, PMV-3, PMV-4, PMV-7, PMV-8 and PMV-9 serotypes; the conception that genomic material coding for the HN glycoprotein consists of a "common-to-all-the-PMVs" portion and a "serotype-specific" portion, on one hand, and of a "conserved" portion and a "variable" portion, on the other; the ratios between the portions have been shown to be different for, at least, certain PMV serotypes; the evolutionary pathways of the avain PMV HN antigenic drift.

Interaction of Newcastle disease virus strains differing in virulence with chicken red blood cell receptors

Nine NDV strains belonging to lentogenic, mesogenic and velogenic groups were studied. Virus adsorption to chicken red blood cell (RBC) surface was performed at 4 degrees C, and after a temperature shift from 4 degrees to 37 degrees C elution of pre-adsorbed virus and accumulation of free N-acetyl-neuraminic acid (NANA) split from RBC receptors as a result of neuraminidase (Nase) activity was detected. In the case of high multiplicity of adsorption the elution was very fast (complete elution within 5 minutes) for all the strains irrespective of their virulence. Although physical saturation of RBC surface with the adsorbed virus was not achieved, a certain minimal (strain-specific) amount of the pre-adsorbed virus which splits a maximally possible (for a given strain) quantity of the NANA was found (a state of "enzymatic saturation"). Below a certain low multiplicity of adsorption elution was delayed for about 20-30 minutes while the accumulation of the split NANA began immediately after the temperature shift. This phenomenon was interpreted as a result of "crawling" of the adsorbed virions upon the RBC surface followed by "browsing" of RBC receptors and liberation of NANA. Thus, the Nase activity of the attached virus ("in situ Nase activity") is a factor providing both elution and "crawling" of the virus (depending on the multiplicity of adsorption). The in situ Nase activity of all the strains used was determined quantitatively by (1) parameters of enzymatic kinetics (Vmax, Km and Km/Vmax) and (2) parameters of enzymatic efficiency related to a certain quantity of the adsorbed virus, namely, per amount of: a) "crawling" virus, b) that providing "enzymatic saturation", and c) that equal to Km. Computation of these parameters revealed inverse correlation between the in situ Nase activity and the strain virulence. Thus, these indications can be in vitro markers of the in vivo virulence.