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Journal of Virology, June 1999, p. 4721-4727, Vol. 73, No. 6
Austrian Academy of Sciences, Institute of
Molecular Biology, A-5020 Salzburg, Austria,1
and University of Kiel, Institute of Biochemistry, D-24098
Kiel, Germany2
Received 9 December 1998/Accepted 5 March 1999
By comparative analysis of the hemagglutinin-esterase (HE) protein
of mouse hepatitis virus strain S (MHV-S) and the HE protein of
influenza C virus, we found major differences in substrate specificities. In striking contrast to the influenza C virus enzyme, the MHV-S esterase was unable to release acetate from bovine
submandibulary gland mucin. Furthermore, MHV-S could not remove
influenza C virus receptors from erythrocytes. Analysis with free
sialic acid derivatives revealed that the MHV-S HE protein specifically
de-O-acetylates 5-N-acetyl-4-O-acetyl sialic
acid (Neu4,5Ac2) but not
5-N-acetyl-9-O-acetyl sialic acid
(Neu5,9Ac2), which is the major substrate for esterases of
influenza C virus and bovine coronaviruses. In addition, the MHV-S
esterase converted glycosidically bound Neu4,5Ac2 of guinea pig serum glycoproteins to Neu5Ac. By expression of the MHV esterase with recombinant vaccinia virus and incubation with guinea pig serum,
we demonstrated that the viral HE possesses
sialate-4-O-acetylesterase activity. In addition to
observed enzymatic activity, MHV-S exhibited affinity to guinea pig and
horse serum glycoproteins. Binding required
sialate-4-O-acetyl groups and was abolished by chemical de-O-acetylation. Since Neu4,5Ac2 has not been identified
in mice, the nature of potential substrates and/or secondary receptors for MHV-S in the natural host remains to be determined. The esterase of
MHV-S is the first example of a viral enzyme with high specificity and
affinity toward 4-O-acetylated sialic acids.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
The Hemagglutinin-Esterase of Mouse Hepatitis Virus
Strain S Is a Sialate-4-O-Acetylesterase
*
Corresponding author. Mailing address: Austrian Academy
of Sciences, Institute of Molecular Biology, Billrothstr. 11, A-5020 Salzburg, Austria. Phone: 43-662-6396124. Fax: 43-662-6396129. E-mail:
rvlasak{at}oeaw.ac.at.
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