Virus influenza

Influenza A infections are responsible for 300-500,000 deaths and 3-5 million hospitalizations per year. Every epidemic brings about new strains of influenza A, which arise due to point mutations within the surface glycoproteins hemagglutinin (HA) and neuraminidase (NA). These mutations in turn enable emerging virus strains to evade the host s immune system. The long production time of the current commercially available vaccine, which is produced in chicken eggs, is a major obstacle. 

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Jedrzejas, M. J., Singh, S. Brouillette, W. J. Air, G. M. Luo, M. A. 1995. Strategy for theoretical binding constant, Ki calculation for neuraminidase aromatic inhibitors, designed on the basis of the active site structure of influenza virus neuraminidase. Proteins Struct. Funct. Genet. 23 (1995) 264-277... 

FIGURE 25 11 Diagram of a cell surface glycoprotein showing the disaccharide unit that IS recognized by an invading influenza virus... 

A second example of up-and-down p sheets is the protein neuraminidase from influenza virus. Here the packing of the sheets is different from that in RBP. They do not form a simple barrel but instead six small sheets, each with four P strands, which are arranged like the blades of a six-bladed propeller. Loop regions between the p strands form the active site in the middle of one side of the propeller. Other similar structures are known with different numbers of the same motif arranged like propellers with different numbers of blades such as the G-proteins discussed in Chapter 13. 

The neuraminidase molecule is a homotetramer made up of four identical polypeptide chains, each of around 470 amino acids the exact number varies depending on the strain of the virus. If influenza virus is treated with the proteolytic enzyme pronase, the head of the neuraminidase, which is soluble, is cleaved off from the stalk projecting from the viral envelope. The soluble head, comprising four subunits of about 400 amino acids each, can be crystallized. 

Figure S.6 Schematic and topological diagrams of the folding motif in neuraminidase from influenza virus The motif is built up from four antiparallel P strands joined by hairpin loops, an up-and-down open P sheet.

Figure S.7 The subunit structure of the neuraminidase headpiece (residues 84-469) from influenza virus is built up from six similar, consecutive motifs of four up-and-down antiparallel fi strands (Figure 5.6). Each such motif has been called a propeller blade and the whole subunit stmcture a six-blade propeller. The motifs are connected by loop regions from p strand 4 in one motif to p strand 1 in the next motif. The schematic diagram (a) is viewed down an approximate sixfold axis that relates the centers of the motifs. Four such six-blade propeller subunits are present in each complete neuraminidase molecule (see Figure 5.8). In the topological diagram (b) the yellow loop that connects the N-terminal P strand to the first P strand of motif 1 is not to scale. In the folded structure it is about the same length as the other loops that connect the motifs. (Adapted from J. Varghese et al.. Nature 303 35-40, 1983.)...

Figure 5.19 Schematic picture of a single subunit of influenza virus hemagglutinin. The two polypeptide chains HAj and HA2 are held together by disulfide bridges.

We have already discussed one envelope protein of influenza virus, neuraminidase, as an example of an up-and-down antiparallel p motif. In the second envelope protein, hemagglutinin, one domain of the polypeptide chain is folded into a jelly roll motif. We shall now look at some other features of hemagglutinin that are important for its biological function. 

Colman, P.M., Varghese, J.N., Laver, W.G. Structure of the catalytic and antigenic sites in influenza virus neuraminidase. Nature 303 41-44, 1983. 

Daniels, R.S., et al. Fusion mutants of the influenza virus hemagglutinin glycoprotein. Cell 40 431-439, 1985. 

Watowich, S.I., et al. Crystal structures of influenza virus haemagglutinin in complex with high affinity receptor analogs. Structure 2 719-731, 1994. 

Wiley, D.C., Skehel, JJ. The structure and function of the hemagglutinin membrane glycoprotein of influenza virus. Annu. Rev. Biochem. 56 365-394, 1987. 

Colman, P.M., et al. Three-dimensional structure of a complex of antibody with influenza virus neuraminidase. Nature 326 358-363, 1987. 

Stern, L.J., Brown, J.H., Jardetzky, T.S., Gorga, J.C., Urban, R.G., Strominger, J.L., Wiley, D.C. Crystal structure of the human class 11 MHC protein HLA-DRl complexed with an influenza virus peptide. Nature 368 215-221,... 

The hemagglutinin protein in influenza virus contains a remarkably long u-helix, with 53 residues. 

Thiopheneglyoxal has been found to be only moderately active against Newcastle disease virus and influenza virus in embryonated eggs. ... 

Amino- and hydrazino-quinazolines exhibited antibacterial ac-tivity and a patent claim on the in vitro action of 2,4-diamino-quinazolines was rnade. The preparation of thiopegan derivatives as potential antimalarials and antibacterials deserves mention. Complete inhibition of influenza virus in vitro but not in vivo was shown by. 6,8-dichloro-2,4-dihydroxyquinazoline and other cyclic ureas. Activity against trachoma virus was also displayed by several 2-trichloromethylquinazolines. ... 

The suspension of influenza virus, strain A/X-53, was separated from the constituents of alantoic fluid by preparative size exclusion chromatography on a 10 x 120 cm column. The hemo-agglutination method revealed an elevated level (93%) of viral activity. The leakage of the bonded phases can be more efficiently minimized, however, with the use of positively charged polymers. 

The influenza virus inhibitors, zanamivir, and oseltamivir, act outside the cell after virus particles have been formed. The dtugs have been designed to fit into the active site of the viral envelope enzyme neuraminidase, which is required to cleave sialic acid off the surface of the producing cells. When its activity is blocked, new virus particles stay attached to the cell surface through binding of the virus protein hemagglutinin to sialic acid and are prevented from spreading to other cells. 

Neuraminidase inhibitors are the major class of drugs to treat or to prevent the infection with influenza viruses. Currently, two neuraminidase inhibitors are available, zanamivir and oseltamivir, which block the release of new influenza vims from infected host cells and thereby stop the spread of infection. The enzyme neuraminidase is a surface glycoprotein present on all influenza viruses. There are nine influenza neuraminidase sub-types known of which subtypes N1 and N2 appear to be the most important ones. Neuraminidase inhibitors are effective against all neuraminidase subtypes. The activity of the neuraminidase is required for the newly... 

Active immunization against the specific influenza virus strains contained in the formulation Same as for BCG vaccine One or two doses of 0.25-0.5 mL IM... 

Bacterial and viral myositis is well recognized as a clinical entity by muscle pathologists. The viruses most commonly involved appear to be the Coxsackie viruses, the arboviruses, influenza virus, and HIV, but the mechanism whereby the viral infection gives rise to the myositic syndrome is not known. A detailed discussion of such problems is presented later on pages 333-334. 

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