The structural basis of the function of influenza virus glycoproteins

A proteomics approach to survey the antigenicity of the influenza virus by mass spectrometry

A proteomics-based approach is described that combines gel electrophoresis and MS in order to identify protein interactions and the nature of the interaction interface with high-sample throughput and sensitivity. Results for protein antigens of the influenza virus have demonstrated that the approach can be successfully employed to detect determinants within the hemagglutinin antigen of two divergent type A forms of the virus in present circulation. The determinants are localised to residues 206-224 following tryptic digestion of the hemagglutinin antigen. Specific peptide-antibody complexes formed after treatment of gel-recovered antigen are shown to be able to be preserved on the MALDI target array as has been previously demonstrated in this laboratory for whole virus. The approach has broad applicability for the analysis of a wide array of protein complexes with identification of the interaction interface in a single step with high-sample throughput and at low sample levels.

The role of carbohydrate in determining the immunochemical properties of the hemagglutinin of influenza A virus

Most of the carbohydrate was removed from influenza virus MRC II (H3N2) and its purified hemagglutinin (HA) on treatment with glycosidases, including alpha-mannosidase, beta-N-acetylglucosaminidase, beta-galactosidase and alpha-fucosidase. The release of 50 per cent of the carbohydrate from intact virus particles significantly affected hemagglutinating activity. The ability of untreated and glycosidase-treated virus to inhibit the binding of antibodies directed against the hemagglutinin was almost indistinguishable by competitive radioimmunoassay (RIA). Up to 60 per cent of the carbohydrate from the purified HA of influenza virus could be removed. The antigenicity of glycosidase treated HA molecules decreased 8-fold compared to intact HAs as measured by competitive RIA. In addition, glycosidase digestion of 125I-labeled HA resulted in a decrease in its reactivity in direct RIA. We conclude that the carbohydrate portion of the HA of influenza virus is not of major importance in defining the antigenicity of HA.

Neuraminidase from influenza virus A (H3N2): specificity towards several substrates and procedure of activity determination

Neuraminidase (acylneuraminyl hydrolase, EC 3.2.1.18) from the influenza virus A/Hong Kong/68 (H3N2) was purified after treatment of the purified virus with sarcosyl (sodium laurylsarcosinate), centrifugation at 110 000 x g, and chromatography on DEAE-Sephadex and Sephadex G-200. It migrated as a single component during electrophoresis on polyacrylamide gel, and its molecular weight was estimated about 270 000. The enzyme was thermolabile, the activity being reduced to 60% in 10 min at 50 degrees C. The purified neuraminidase had an apparent Km value of 4.1 . 10(-3) M for 5-N-acetyl-2-O-(3-methoxyphenyl)-alpha-D-neuraminic acid and was able to release sialic acid with linkages alpha 2-3, alpha 2-6 and alpha 2-8 (with very different efficiency) from fetuin, gangliosides, colominic acid, and bovine and porcine submaxillary mucins. The enzymic activity was measured by several procedures: (A) spectrophotometric determination at 340 nm of the NADH produced in the reaction catalysed by beta-galactose dehydrogenase on beta-galactose + NAD+, this beta-galactose was the product released from lactose by beta-galactosidase and lactose was the product of the neuraminidase activity on N-acetylneuraminyl-lactose; (B) determination of the colored quinone yielded by the liberated methoxyphenol with 4-aminoantipyrine (Santer, U.V., Yee-Foon, J. and Glick, M.C. (1978) Biochim. Biophys. Acta 523, 435-442); (C) periodate-thiobarbiturate procedures (Warren, L. (1959) J. Biol. Chem 234, 1971-1975 or Aminoff, D. (1961) Biochem. J. 81, 384-391). Some peculiarities of these methods are discussed.

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.

Influenza virus-specific T cell-mediated cytotoxicity: integration of the virus antigen into the target cell membrane is essential for target cell formation

This study deals with the requirements for target cell recognition by influenza A virus-specific cytotoxic T lymphocytes (CTL). H-2-identical cells were incubated with infectious or UV light-inactivated influenza A virus expressing either cleaved or uncleaved hemagglutinin (HA). Thereafter, the treated cells were tested in a 4-h 51Cr assay for susceptibility to CTL-mediated cytolysis. Regardless whether the influenza virus was infectious, virions expressing cleaved HA were efficient in target cell formation. In contrast, cells incubated with either active or UV-inactivated virions expressing uncleaved HA were not lysed by virus-specific CTL. Yet, after mere trypsin-mediated cleavage of the HA of cell-absorbed viroins, strong cytolysis could be observed. On the other hand, solubilization of the envelope lipid bilayer by ethylether abolished the capacity of the remaining HA to induce target cell formation. The results clearly suggest that mere absorption of virions to the membrane of cells, which is performed by virus with uncleaved HA, is insufficient for target cell formation. For this, both cleaved HA and an intact envelope appear to be crucial. We conclude that fusion of the virion into the cell membrane is essential for target cell formation.