STERIC INHIBITION: NEUTRALIZATION OF A VIRUS-BORNE ENZYME

Influenza A virus hemagglutinin specific antibodies interfere with virion neuraminidase activity via two distinct mechanisms

We studied the ability of monoclonal Abs (mAbs) recognizing the major hemagglutinin (HA) antigenic sites to inhibit neuraminidase (NA) cleavage of sialic acids on fetuin. We show that virion associated-NA activity in the enzyme linked lectin assay (ELLA) is largely dependent on HA-mediated attachment of virions to immobilized fetuin. For a Sb-antigenic site specific mAb, there is a nearly perfect correlation between neuraminidase inhibition and blocking virus attachment to immobilized fetuin. By contrast, Sa-, Ca-, and Cb- antigenic site specific mAbs block NA activity in ELLA or the traditional thiobarbituric acid assay by sterically interfering with NA access to substrate. We conclude first, that ELLA with intact virus can only be used to measure anti-NA Abs if sera lack HA-specific Abs, and second, that anti-HA Abs block NA activity by both limiting virion interaction with sialic acid containing surfaces and by sterically limiting NA access to sialic acids attached to macromolecules.

Venom exonuclease. III. Immunochemical characterization and modification by specific antibody

The immunoelectrophoretic purity of the exonuclease preparation, isolated from Crotalus adamanteus venom according to a procedure previously published (Dolapchiev, L.B., Sulkowski, E. and Laskowski, M., Sr. (1974) Biochem. Biophys. Res. Commun. 61, 271-281), is reported. The enzyme showed one precipitin line against antibody prepared against partially purified venom. The exonuclease is unstable in dilute (1.25 microgram/ml and below) solutions. Bovine serum albumin stabilized the enzyme nonspecifically whereas the homologous antibody demonstrated a specific stabilizing effect under the same conditions. The binding of the anti-enzyme with the enzyme caused inhibition of both its activities--phosphodiesterase and pyrophosphatase. The inhibition of the exonuclease when attacking high molecular weight substrates is similar to the above and is of the same noncompetitive type. The thermal stability of venom exonuclease is reported.

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.

Effect of Ca++ on the stability of influenza virus neuraminidase

The neuraminidases of different strains of influenza virus varied in their stability at 37 degrees C. The enzymes of the strains with N1 neuraminidases were found to be unstable during incubation at 37 degrees C whereas the enzymes of the strains with the N2 neuraminidases were stable. Among the strains with N2 neuraminidases, the enzymes of some strains were inactivated during dialysis at 37 degrees C whereas the enzymes of others were stable. This observed loss of enzyme activity during dialysis at 37 degrees C was not restricted to a single substrate as the same loss of enzyme activity was observed irrespective of the size of the substrate used in the assay. The enzymically inactive neuraminidase was found to be non-antigenic and non-immunogenic. The inactivation of the enzyme could be prevented by the addition of Ca++ but not Mg++. Out results suggest that Ca++ is essential for the stability of the enzyme at 37 degrees C. The results would also suggest that the enzymic, antigenic and immunogenic sites are either the same or very closely situated on the surface of the neuraminidase molecule.