Structural homology between hemagglutinin (HA) of measles virus and the active site of long neurotoxins.

The amino acid sequence of a carboxy terminal domain corresponding to the end of the outer envelope projection of the hemagglutinin glycoprotein (HA) of measles and subacute sclerosing panencephalitis viruses has a high degree of homology with the active domain of long neurotoxins, which specifically binds to the nicotinic acetylcholine receptor. The homology in amino acid sequence of HA to this domain of neurotoxin, as well as native alpha-bungarotoxin (BTx), was confirmed by the following evidence: a) rabbit anti-HA monospecific sera reacted with BTx in ELISA, b) HA dose-dependently blocked the binding of radio-labeled BTx in competitive radioimmunoassay, and c) antibody to a synthetic peptide of the active domain of BTx precipitated HA in radioimmunoprecipitation. In addition, SSPE patients had significantly high titers of antibody to BTx than healthy children who had been previously infected with measles. This epitope of HA may play an important role in the transsynaptic spreading of the virus in the brain.