Amino acid change 335 E to K affects the sialic-acid-binding and neuraminidase activities of Urabe AM9 mumps virus hemagglutinin-neuraminidase glycoprotein

A mutation coding for the amino acid change E-335 to K is frequently found in the hemagglutinin-neuraminidase (HN) gene of Urabe AM9 mumps viruses isolated during post-vaccination meningitis cases. To identify if this mutation modifies the biological activities of the HN glycoprotein, two variants of Urabe AM9 vaccine differing at amino acid 335 (HN-E-335 and HN-K-335) were isolated and their receptor-binding specificity was determined by means of competence assays. Pre-incubation of the viruses with sialic acids inhibited both syncytia formation in Vero cells and replication in SH-SY5Y cells. Thus, HN-K-335 showed higher affinity towards sialyl alpha 2,61actose, whereas HN-G(335) preferred sialyl alpha 2,31actose. These results are relevant because a high expression of sialyla2,61actose in nerve cells was confirmed by means of Sambucus nigra lectin-cytochemistry. In addition, kinetics assays showed that HN-K-335 and HN-E-335 also differ in their hydrolysis rate (V-max, values of 37.5 vs. 3.5 nmol min(-1) mg(-1), respectively). Therefore, HN-K-335 variant presented a neuraminidase activity level 11-fold higher than that of HNE335 variant. In conclusion, the mutation affects the receptor-binding and neuraminidase activities of Urabe AM9 mumps virus variants. (c) 2006 Elsevier Masson SAS. All rights reserved.