The chemical reactions of the haemagglutinins and neuraminidases of different strains of influenza viruses. 3. Effects of proteolytic enzymes

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.

Purification of neuraminidase from influenza viruses by affinity chromatography

The neuraminidase (acylneuraminyl hydrolase, EC 3.2.1.18) of the influenza virus recombinant strain (HON2) was solubilized with detergents and isolated by affinity chromatography. The neuraminidase could be purified to a single high molecular weight glycoprotein when assayed under non-reducing conditions on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The enzyme showed an increase in specific activity from 2.46 to 189 micronM N-acetylneuraminic acid released per min per mg protein and the recovery represented 123% of the activity of intact virus particles. The enzyme could be purified from laboratory preparations of virus or from outdated influenza virus vaccine. Viral neuraminidases purified by this technique were stable at pH 6.0 for several hours.

[Isolation of surface antigens of influenza virus A/Hong Kong 1/68 (H3N2) by density gradient fractionation with a new carboxypolypeptidase (author's transl)]

Isolation of pure neuraminidase and hemagglutinin from influenza virus A/Hong Kong 1/68 (H3N2) can be achieved using the coupled action of a new carboxypolypeptidase from Streptomyces fradiae and sodium dodecyl sulfate (SDS). Biochemical, physical and physico-chemical studies showed that the two molecules are in pure form and of glycoproteic nature.

Characterization of influenza virus neuraminidases: peptide changes associated with antigenic divergence between early and late N2 neuraminidases

Neuraminidases (EC 3.2.1.18) of 1957, 1960, and 1969 influenza virus strains were isolated after proteolytic digestion of viral hemagglutinin. Each neuraminidase was recovered with a final yield of about 15% and had similar specific activities. Immunization of rabbits with the neuraminidases elicited monospecific neuraminidase antibodies, with no antibodies to viral hemagglutinin. Further evidence of purity was the existence of only a single component, about 50,000 daltons in size, when reduced neuraminidase preparations were examined by sodium dodecyl sulfate acrylamide gel electrophoresis. However, storage of neuraminidase in solution resulted in the appearance of slightly smaller degradation products. Preparations of each neuraminidase were denatured under reducing conditions, and exposed sulfhydryl residues were blocked by reaction with (14)C-iodoacetamide. After tryptic digestion, peptide maps were prepared for the neuraminidases, and the (14)C-labeled cysteinyl peptides were then identified by autoradiography. About 20 peptides were present, in agreement with the number predicted from amino acid analysis for neuraminidase subunits of only one type. The 1957 and 1960 neuraminidases exhibited a small antigenic divergence from each other, and maps of their cysteinyl peptides appeared to be identical. The 1969 neuraminidase exhibited considerable antigenic divergence from the other two neuraminidases, and maps of 1969 neuraminidase peptides revealed two major and several minor differences from the other maps. Thus, antigenic divergence between the neuraminidases of Asian and Hong Kong influenza viruses is associated with a small number of changes in the primary structure of the neuraminidase subunit.