Subunits of NDV: Hemagglutinin and neuraminidase subunits of Newcastle disease virus

Abstract

When purified Newcastle disease virus (NDV) was treated with deoxycholate (DOC), two major surface antigens of the virus, hemagglutinin and neuraminidase, were released in biologically active form and the respective antigens could be separated by sucrose gradient centrifugation into two distinct bands. The hemagglutinin subunits obtained by the DOC method were reactive with hemagglutination-inhibiting antibody but did not agglutinate red blood cells even after they were freed from DOC by dialysis. Thus, they appeared to be monovalent. However, they acquired the capacity to agglutinate red blood cells, when they were mixed with the top fraction of the sucrose gradient through which the DOC-disrupted virus had been centrifuged, or by the addition of a phospholipid, phosphatidylethanolamine. Electron microscopic examination of the hemagglutinin subunits revealed filamentous structures associated with several projections on both sides. These results suggested that polymerization of the monomeric subunits occurred, not directly end to end, but mediated through the filament which might be phospholipid in nature.