Electron microscopy of purified influenza virus neuraminidase

Structure of bromelain-released influenza virus haemagglutinin as revealed by electrophoresis, sedimentation and electron microscopy

Sigma bromelain (EC 3.4.22.4) was used to isolate the haemagglutinin (HA) from the MRC-11 (H3N2) and A/U.S.S.R./90/77 (H1N1) influenza A virus strains. Sedimentation analysis of bromelain-solubilized preparations revealed 9.5S and 5.5S protein components, the former being identified as the bromelain-released haemagglutinin (BHA). No residual neuraminidase (NA) activity was detected in the BHA isolated from the MRC-11 strain whereas up to 80 per cent of the enzymatically active NA was found to be preserved in the electrophoretically pure BHA isolated from the A/U.S.S.R./90/77 strain. Increased electrophoretic mobilities were exhibited by both the light and heavy chains of the BHA subunit. The difference observed in the molecular weights of the polypeptide fragments removed by bromelain from the light chains is interpreted in terms of the different depth of penetration of antigenically distinct HAs through the influenza virus lipid membrane. Splitting off of approximately 15 and 26 per cent of the sugars from the carbohydrate portions of the light and heavy chains respectively, was demonstrated. This suggested involvement of glycosidase impurities present in the bromelain preparation employed. The rod-shaped BHA molecules proved to be 110 +/- 5 Angstrom long and 40 +/- 5 Angstrom wide as measured by electron microscopy. It is proposed that the 45,000-molecular-weight polypeptide observed constantly in egg-grown influenza viruses is host actin.

Thermal inactivation of Newcastle disease virus. I. Coupled inactivation rates of hemagglutinating and neuraminidase activities

The thermal stability of Newcastle disease virus has been characterized in terms of the rate constants for inactivation of hemagglutinating activity (HA), neuraminidase activity (NA), and infectivity. Inactivation of HA results in the concomitant loss of NA. Infectivity, however, is much more thermolabile. Disintegration of the virus particle is not responsible for the identical rate constants for inactivation of HA and NA, nor is their parallel inactivation uncoupled in envelope fragments produced by pretreating the virus with phospholipase-C. The data indicate that a common envelope factor(s) can influence the thermal stability of both activities.

Distribution of neuraminidase and n-acetylneuraminate lyase activities among corynebacteria, mycobacteria, and nocardias

In Corynebacterium diphtheriae and closely related neuraminidase-producing corynebacteria, we have found an N-acetylneuraminate (NAN) lyase activity which cleaves NAN into N-acetyl-d-mannosamine and, presumably, pyruvate. In vitro, these lyases can be shown to synthesize NAN. A survey of representative corynebacteria, "plant pathogenic corynebacteria," mycobacteria, and nocardias revealed that only those corynebacteria closely related to C. diphtheriae exhibited both neuraminidase and NAN lyase activities.

Models of structure of the envelope of influenza virus

Possible models of the structure of the influenza virus envelope are considered in terms of the known chemical composition. Models incorporating lipid in the form of a bimolecular leaflet are shown to be unlikely on geometrical grounds. A model having "inverted toadstool" protein units separated by spherical lipid micelles is favored, and is capable of explaining the appearance of the virus in the electron microscope and differences between normal and incomplete (von Magnus) forms of the virus.

Disruption of myxoviruses with Tween 20 and isolation of biologically active hemagglutinin and neuraminidase subunits

Myxoviruses were disrupted with Tween 20 at high pH, and the major surface antigens were separated in biologically active form. The neuraminidase had a sedimentation coefficient of 10.8S, and the hemagglutinin had a sedimentation coefficient of 8.1S. Electron microscopic examination of negatively stained preparations revealed structures identical in size and morphology to the neuraminidase and hemagglutinin subunits described by others. Inhibition of neuraminidase activity by antibody to the hemagglutinin which occurred with intact viruses (probably for "steric" reasons) did not occur after the viruses were disrupted with Tween 20. Serological assays for neuraminidase were possible in the presence of the mild surfactant, whereas serological assays for hemagglutinin were possible after removal of the reagent. Disruption of myxoviruses with Tween 20 therefore provides a method for the independent study of these antigens during antigenic drift.