Identification of a Coronavirus Hemagglutinin-Esterase with a Substrate Specificity Different from Those of Influenza C Virus and Bovine Coronavirus

Abstract

ABSTRACT We have characterized the hemagglutinin-esterase (HE) of puffinosis virus (PV), a coronavirus closely related to mouse hepatitis virus (MHV). Analysis of the cloned gene revealed approximately 85% sequence identity to HE proteins of MHV and approximately 60% identity to the corresponding esterase of bovine coronavirus. The HE protein exhibited acetylesterase activity with synthetic substrates p -nitrophenyl acetate, α-naphthyl acetate, and 4-methylumbelliferyl acetate. In contrast to other viral esterases, no activity was detectable with natural substrates containing 9- O -acetylated sialic acids. Furthermore, PV esterase was unable to remove influenza C virus receptors from human erythrocytes, indicating a substrate specificity different from HEs of influenza C virus and bovine coronavirus. Solid-phase binding assays revealed that purified PV was unable to bind to sialic acid-containing glycoconjugates like bovine submaxillary mucin, mouse α 1 macroglobulin or bovine brain extract. Because of the close relationship to MHV, possible implications on the substrate specificity of MHV esterases are suggested.