Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.4 (trypsin)
 42,187 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

One of the unresolved questions concerning the acquisition of virulence by the A/Chicken/Pennsylvania/83 (H5N2) influenza virus is which gene segments other than the hemagglutinin (HA) showed changes that were relevant. To answer this question, reassortants were made possessing the hemagglutinin gene of the virulent virus and the seven other genes from the avirulent parent. Since both the virulent and avirulent H5N2 strains are antigenically almost indistinguishable, it was necessary to transfer the genes of interest to a "carrier" virus before the appropriate reassortment could be selected. The gene compositions of the reassortants was established by a combination of sequence analysis and migration on polyacrylamide gels. These analyses established that the avirulent influenza virus present in April 1983 possessed seven of the eight gene segments necessary for virulence; mutation(s) in the HA gene were required for acquisition of virulence. Other viruses such as A/Seal/Mass/1/80 (H7N7) could provide the other genes necessary for virulence. Two changes in the HA have been associated with the acquisition of virulence; these are at amino acid residues 23 and 78 (H3 numbering) (Y. Kawaoka and R.G. Webster, Virology, 146, 130-137 (1985]. Isolation of an amantadine-resistant avirulent revertant virus provided the opportunity to determine which of the two amino acid changes in HA is critical. Sequence analysis of the revertant virus revealed amino acid changes at residues 23 in HA1 and 40 in HA2 (H3 numbering). The change at residue 23 of HA1 is probably associated with reversion to avirulence, of cleavability of HA, and inability to plaque in tissue culture without trypsin; while the change at residue 40 of HA2 may be associated with the amantadine-resistant phenotype. These studies establish that a single critical point mutation in the hemagglutinin gene of the avirulent A/Chicken/Pennsylvania/1/83 (H5N2) was probably all that was required to produce the highly virulent Chicken/Pennsylvania virus; the avirulent virus already possessed the other genes necessary for virulence.
 ...
PMID:Molecular changes in A/Chicken/Pennsylvania/83 (H5N2) influenza virus associated with acquisition of virulence. 394 82

We have measured the infectivity of influenza A virus strains grown either in embryonated eggs or in chick embryo cells in culture after treatment at low pH. At pH values at which hemolysis occurs there was an irreversible loss of infectivity. The threshold pH, at which the infectivity was lost, depended on the hemagglutinin subtype of the virus strain. All H5 and H7 strains tested were extremely labile at low pH. In contrast, all H3 strains were relatively stable, independent of the species from which the viruses were isolated. With several H1 viruses the hemagglutination (HA) activity was irreversibly lost at intermediate pH values causing inactivation of infectivity. Strains with noncleaved hemagglutinins were much more stable. These observations might explain why duck influenza viruses can easily survive in lake water and wet faeces, and multiply in the intestinal tract, where trypsin is present. There are also significant differences in heat stability exhibited by influenza A strains. In contrast to pH stability this is not a specific trait of the hemagglutinin, since it can be influenced by reassortment. There is no correlation between the stability of infectivity at low pH and heat.
 ...
PMID:Stability of infectious influenza A viruses to treatment at low pH and heating. 401 5

The pH-dependent fusion between influenza virus and liposomes (large unilamellar vesicles) has been investigated as a model for the fusion step in the infectious entry of the virus into cells. Fusion was monitored continuously, with a fluorescence assay based on resonance energy transfer (RET) [Struck, D. K., Hoekstra, D., & Pagano, R. E. (1981) Biochemistry 20, 4093-4099], which allows an accurate quantitation of the fusion process. Evidence is presented indicating that the dilution of the RET probes from the liposomal bilayer into the viral membrane is not due to transfer of individual lipid molecules. The initial rate and final extent of the fusion reaction increase dramatically with decreasing pH, fusion being virtually complete within 1 min at pH 4.5-5.0. From experiments in which the ratio of virus to liposomes was varied, it is concluded that virus-liposome fusion products continue to fuse with liposomes, but not with virus. Fusion is most efficient with liposomes consisting of negatively charged phospholipids, while phosphatidylcholine and sphingomyelin are inhibitory. The reaction is completely blocked by an antiserum against the virus and inhibited by pretreatment of the virus with trypsin. The effect of proteolytic pretreatment at pH 7.4 is enhanced after preincubation of the virus at pH 5.0, consistent with the occurrence of a low pH induced, irreversible, conformational change in the viral fusion protein, the hemagglutinin (HA), exposing trypsin cleavage sites. When, after initiation of the fusion reaction at pH 5.0, the pH is readjusted to neutral, the process is arrested instantaneously, indicating that the low pH induced conformational change in the HA protein, in itself, is not sufficient to trigger fusion activity.
 ...
PMID:Kinetics of pH-dependent fusion between influenza virus and liposomes. 402 33

Complete nucleotide sequence of the cloned full-length DNA copy of the influenza virus A (H1N1) RNA segment 8 has been determined. A section of the hypothetical protein coded for by the negative strand of the segment 8 is found to be homologous to the trypsin catalytic centre.
 ...
PMID:[Synthesis, cloning and determination of the primary structure of a full-size DNA copy of fragment 8 from the influenza virus type A genome]. 403 50

Neuraminidase (N) can be extracted from virus particles of influenza B strains by treatment with trypsin, in a form which is free from the viral HA and has specific immunological activity. The N antigen of B/LEE/40 behaves differently from that of 1965-6 strains in gel diffusion and enzyme inhibition tests with animal antisera raised by infection or by artificial immunization with the homologous or heterologous strains. The frequency and titres of NI antibody detected in human sera by B/LEE antigen are different from those found with antigen from B/Eng/13/65. The latter antibody appears to contribute to the effect of serum HI antibody in protecting volunteers exposed to a deliberate intranasal challenge infection of the B/Eng/13/65 strain.
 ...
PMID:Serological studies with purified neuraminidase antigens of influenza B viruses. 420 35

Serum is commonly treated with potassium periodate to destroy nonspecific inhibitors of influenza virus hemagglutination. We have observed, however, that such treatment of serum without pre-existing inhibitor produced high titers of inhibitor against certain strains of influenza virus. Inhibitor was induced in the serum from several different animal species but not in hamster or mouse serum. Periodate treatment of serum albumin, fraction V, from several animals, including man, creates this inhibitor. Our data indicate that the inhibitor induced in the serum of various animal species differs in its mechanism of induction and in its resistance to receptor-destroying enzyme and trypsin. Hemagglutination by B/Singapore/3/64, B/Colorado/2/65, B/Georgia/1/65, and B/Massachusetts/3/66 strains of influenza virus is inhibited by periodate-treated human serum at dilutions as high as 1:5,120. The routine use of periodate treatment of serum in diagnostic and surveillance studies of influenza virus infections is not recommended.
 ...
PMID:Induction of an inhibitor of influenza virus hemagglutination by treatment of serum with periodate. 429 11

By in vivo and in vitro methods of immunofluorescence, antibody to rat collagen and to rat kidney show the same regular, linear fluorescence following the outlines of the renal glomerular capillaries. Absorption of each antiserum with its homologous antigen completely removed the antibody for immunofluorescence, while absorption with the heterologous antigen had no effect. The nephrotoxicity persisted in the anti-kidney serum absorbed with collagen. By pretreatment of frozen normal rat kidney sections with various enzymes followed by immunofluorescence, it was shown that trypsin and hyaluronidase had no effect on the subsequent fluorescence of either antibody; papain reduced the fluorescence; and pepsin and Pronase acted on both antigens so that no fluorescence was present. One preparation of neuraminidase, derived from V. cholerae, reduced fluorescence of both antibodies in some preparations, but the same enzyme derived from influenza virus or C. perfringens had no effect on either. Collagenase completely prevented fluorescence of the antibody to collagen and had no effect on that to rat kidney. The findings in this study show that the antibody to collagen is directed to collagen in rat renal glomerular basement membranes and that the antibody to rat kidney reacts with some antigen other than collagen in these membranes.
 ...
PMID:Comparison of reactions of antibodies to rat collagen and to rat kidney in the basement membranes of rat renal glomeruli. 430 40

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.
 ...
PMID:Inactivation of the hemagglutinins of type A influenza viruses by physical and chemical means: an aid to classification. 467 70

Biological properties of the Hong Kong influenza variants are described in relation to the isolation and identification of strains, sensitivity to nonspecific inhibitors, and serological diagnosis. Hong Kong virus strains were readily isolated in both eggs and monkey-kidney tissue cultures and were identified by haemagglutination-inhibition (HI) with chicken erythrocytes. The morphology, soluble antigen, and neuraminidase of Hong Kong isolates were similar to those of earlier A2 Asian influenza strains. Hong Kong haemagglutinins were related in varying degrees to previous human A2 and animal influenza viruses.The sensitivity of Hong Kong isolates to nonspecific haemagglutination inhibitors in serum varied widely. From least to most inhibitory, the ranking of sera of 8 animal species tested was: monkey, goat, chicken, human, rabbit, ferret, guinea-pig and horse. The same sera were treated with heat, trypsin, periodate, receptor-destroying enzyme and kaolin to determine the most effective way of removing nonspecific inhibitors. The results varied with the animal species involved.The A2 Asian antigen was nearly as effective as Hong Kong antigen in detecting antibody rises by HI tests. HI tests with either antigen were more efficient than complement-fixation tests for serodiagnosis of Hong Kong influenza, but for maximum efficiency both tests were required.
 ...
PMID:Properties of the Hong Kong influenza virus. I. General characteristics of the Hong Kong virus. 498 76

The distribution of specific glycoprotein receptors on the external surfaces of red cells was mapped, by the freeze-etching technique, to determine if the receptors coincided with the underlying 75-A intramembranous particles. Phytohemagglutinin, ferritin-conjugated phytohemagglutinin, and influenza virus were used as labeling agents since they can be seen by freeze-etching techniques and each reacts with a different site on the same glycoprotein molecule. The distribution of these labels was studied on intact human red cells, isolated ghost membranes, and trypsin-treated ghost membranes. The results show that the receptors for these labels are distributed uniformly over the surfaces of normal red cell membranes in the same apparent distribution as that of the 75-A particles within the membrane. The association between the external receptors and the underlying particles is especially evident when trypsin-treated ghost membranes are labeled: the labeled receptor sites and the intramembranous particles both form sharply defined, reticulated networks, which overlap. These results provide further support for the idea that membrane-bound glycoproteins are oriented so that their carbohydrate-rich segments, which bear the antigenic sites and receptors, are exposed to the external medium, while hydrophobic segments of the same molecules interact with lipids, and possibly other proteins, to form the intramembranous particles.
 ...
PMID:The structure of erythrocyte membranes studied by freeze-etching. II. Localization of receptors for phytohemagglutinin and influenza virus to the intramembranous particles. 502 37


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>