The chemical reactions of the haemagglutinins and neuraminidases of different strains of influenza viruses. II. Effects of reagents modifying the higher order structure of the protein molecule

Preparation-conditioned changes of the antigenicity of influenza virus neuraminidases

The influenza virus strains A/Sing/1/57 (H2N2), A/Bel/42 (H0N1) and A/Bel/42 (HO)-A/Sing/1/57 (N2) were treated with bromelain under reducing conditions and with reducing agent alone, and the antigenicity of the neuraminidase (NA) of intact virus and of the split products was tested comparatively. It was found that the antigenicity of NA was influenced quantitatively and qualitatively by the preparation procedure. Antineuraminidase (AN) antibodies obtained after vaccination of guinea pigs with intact virus and with split products differed in their cross-reactivity with heterologous neuraminidases. In several cases, the quantity of AN antibody formation depended on the hemagglutinin (HA) dose present in the vaccines. The N2 NA on the recombinant virus was significantly more sensitive to treatment with reducing agent than was the N2 NA on the parent virus. AN antibodies directed against N2 NA on the recombinant differed qualitatively from that directed against N2 NA of parent virus. The results warrant the conclusion that the antigenicity of isolated NA or of NA on recombinant virus can differ from that of the NA on intact homologous virus and that such alterations could influence the determination of antigenic relationship between neuraminidases.

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.

Inactivation of the hemagglutinins of type A influenza viruses by physical and chemical means: an aid to classification

The effects of temperature and treatment with sodium dodecyl sulfate, Tween 20, dithiothreitol, trypsin, or guanidine on the hemagglutinating capacity of six strains of type A influenza virus (A(0)/PR8/34, A(1)/CAME/46, A(2)/J305/57, A(2)/Bethesda/63, A(2)/HK/Aichi/68, and A(2)/HK/80/68), one strain of swine virus (A/Swine/76/?), and one equine strain (A/Equi-2/63) were determined. The two Hong Kong strains could be readily distinguished from the earlier A(2) strains by the resistance of their hemagglutinins to trypsin treatment and their inability to recover hemagglutinating capacity after removal of dithiothreitol from treated virus preparations. In these respects, the equine strain most closely resembled the Hong Kong variants. The pattern of hemagglutination inactivation also set the swine, PR8, and CAME strains apart from each other as well as from the other five strains. The results suggest that separation of type A viruses into groups by the pattern of inactivation of their hemagglutinins may be a valuable adjunct to standard serology for a more definite classification of these viruses.

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

The action of trypsin and pronase on the haemagglutinins and neuraminidases of eight strains of influenza virus has been examined.The haemagglutinins of all the strains were highly susceptible to digestion by pronase but there were great variations in resistance to trypsin.The neuraminidases of the eight strains were of three types. The neuraminidases of the A 1 strains and the DSP strain of virus A were highly susceptible to destruction by both enzymes. The neuraminidases of the PR 8 and Swine strains showed partial resistance especially to trypsin, while the A 2 strains and the LEE strains of virus B possessed neuraminidases that were completely resistant to both trypsin and pronase.Proteolytic enzymes released free neuraminidases from the A 2 and LEE viruses the morphology of which was different from that of neuraminidases released by detergent treatment.

The chemical reactions of the haemagglutinins and neuraminidases of different strains of influenza viruses. I. Effect of reagents reacting with amino acids in the active centres

Studies of the chemical reactions of the haemagglutinins and neuraminidases of eight strains of influenza viruses have been made by the use of chemical reagents reacting with chemically active groups in the protein molecule. The results indicate a close resemblance between the active centres of the haemagglutinins and neuraminidases in all the strains tested. In all cases the activities were unaffected by reagents reacting with the —SH group of cysteine, the —CH3S group of methionine, the amino group of lysine, the guanidyl group of arginine, or the indole ring of tryptophan. In all cases both the haemagglutinating and enzymic activities were reduced or destroyed by agents reacting with amide groups or reacting with both tyrosine and histidine.

By the use of iodine under conditions in which tyrosine reacts but not histidine, and fluorodinitrobenzene under conditions in which histidine reacts more strongly than tyrosine, it was possible to detect a number of different active centres.

(1) An active centre containing histidine and an amide group but not containing tyrosine was present in all the virus strains and was the only centre detectable in A1 and A2 strains. This type of centre appeared to possess both haemagglutinating and neuraminidase activity.

(2) Active centres containing tyrosine and an amide group were detected in strains of A and B viruses. There was some evidence suggesting that tyrosine-containing centres were of two types: one possessing both haemagglutinating and enzymic activity while the other was a haemagglutinin without neuraminidase activity.

The results could be explained by supposing that the presence of histidine in the active centre was essential for neuraminidase activity and that enzymically active tyrosine-containing centres also contained histidine, but that tyrosine could substitute for histidine, but that tyrosine could substitute for histidine in haemagglutinating centres.