Anomalous Behaviour of Newcastle Disease Virus Haemagglutinin-Neuraminidase Protein in Western Blotting Analysis of Monoclonal Antibody Binding Sites

Abstract

Previous studies with a particular monoclonal antibody (MAb 445) raised against the Ulster strain of Newcastle disease virus (NDV) have shown that this MAb immune-precipitates only the 74,000 mol. wt. (74K) haemagglutinin-neuraminidase protein (HN) of both Ulster and Beaudette C strains of NDV. Using the technique of Western blotting, it is shown that under certain denaturing conditions virion proteins co-migrating in SDS-polyacrylamide gels with the faster migrating 67K fusion protein and 53K nucleocapsid/nucleocapside-associated protein, as well as the 74K HN, all reacted strongly with MAb 445 and with MAb 14 which is also directed against the HN protein. Analysis of this anomalous behaviour using SDS-polyacrylamide diagonal gel electrophoresis has led to the unexpected conclusion that the 74K HN can electrophorese as three immunoreactive species of apparent mol. wt. 74K, 67K and 53K. If the Western blotting technique is to be applied to proteins which have not been sufficiently denatured (in an attempt to preserve epitope integrity) it is important to establish that no additional proteins remain associated with the protein bands that react with the MAb.