Post-translational modification of the myxoma-virus anti-inflammatory serpin SERP-1 by a virally encoded sialyltransferase.
SERP-1 is a secreted serpin (serine-proteinase inhibitor) encoded by myxoma virus, a poxvirus pathogen of rabbits. SERP-1 is required for myxoma-virus virulence, and the purified protein has been shown to possess independent anti-inflammatory activity in animal models of restenosis and antigen-induced arthritis. As an inhibitor of serine proteinases, SERP-1 acts against tissue-type plasminogen activator, urokinase-type plasminogen activator, plasmin, thrombin and Factor Xa. In the present study, examination of SERP-1 glycosylation-site mutants showed that the N-linked glycosylation of Asn(172) was essential for SERP-1 secretion, whereas mutation of Asn(99) decreased secretion efficiency, indicating that N-linked glycosylation plays an essential role in the processing and trafficking of SERP-1. Furthermore, comparison of SERP-1 from wild-type myxoma virus and a virus containing a targeted disruption of the MST3N sialyltransferase locus demonstrated that SERP-1 is specifically modified by this myxoma-virus-encoded sialyltransferase, and is thus the first reported viral protein shown to by modified by a virally encoded glycosyltransferase. Sialylation of SERP-1 by the MST3N gene product creates a uniquely charged species of secreted SERP-1 that is distinct from SERP-1 produced from other eukaryotic expression systems, though this has no apparent effect upon the kinetics of in vitro proteinase inhibition. Rather, the role of viral sialylation of SERP-1 likely relates to masking antigenicity or targeting SERP-1 to specific sites of action in vivo.
Nash
P
P
Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Barry
M
M
Seet
B T
BT
Veugelers
K
K
Hota
S
S
Heger
J
J
Hodgkinson
C
C
Graham
K
K
Jackson
R J
RJ
McFadden
G
G
D000595:Amino Acid Sequence; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000737:chemistry / Q000378:metabolism*; D001216:Asparagine / Q000378:metabolism; D002460:Cell Line; D006031:Glycosylation; D006596:Hexosaminidases / Q000378:metabolism; D006801:Humans; D007525:Isoelectric Focusing; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D009233:Myxoma virus / Q000201:enzymology*; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D011233:Precipitin Tests; D011499:Protein Processing, Post-Translational; D015843:Serpins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012799:Sialyltransferases / Q000378:metabolism*; D010959:Tissue Plasminogen Activator / Q000378:metabolism; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D000893:Anti-Inflammatory Agents; D015843:Serpins; D014764:Viral Proteins; D001216:Asparagine; D012799:Sialyltransferases; D006596:Hexosaminidases; D010959:Tissue Plasminogen Activator; D019158:N-Acetylneuraminic Acid