Identification of a coronavirus hemagglutinin-esterase with a substrate specificity different from those of influenza C virus and bovine coronavirus

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 prot eins 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, alpha-naphthyl acetate, and 4-m ethylumbelliferyl acetate. In contrast to other viral esterases, no activit y was detectable with natural substrates containing 9-O-acetylated sialic a cids. Furthermore, PV esterase was unable to remove influenza C virus recep tors from human erythrocytes, indicating a substrate specificity different from HEs of influenza C virus and bovine coronavirus. Solid-phase binding a ssays revealed that purified PV was unable to bind to sialic acid-containin g glycoconjugates like bovine submaxillary mucin, mouse alpha(1) macroglobu lin or bovine brain extract. Because of the close relationship to MW, possi ble implications on the substrate specificity of MHV esterases are suggeste d.