Inhibitory specificity of the anti-inflammatory myxoma virus serpin, SERP-1

Piers Nash, Adrian Whitty, Jason Handwerker, Joanne Macen, Grant McFadden

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85 Scopus citations


SERP-1 is a myxoma virus-encoded serpin, secreted from infected cells, that is required for virulence and has anti-inflammatory activity. We report that purified recombinant SERP-1 forms SDS-stable complexes with urokinase- type plasminogen activator (uPA), tissuetype plasminogen activator (tPA), plasmin, thrombin, and factor Xa. N-terminal sequencing confirmed Arg319- Asn320 as the site of reaction. Mutation of these residues to Ala-Ala abolished inhibitory activity but had no effect on the specific cleavage at Thr315-Leu316 seen with elastase and with cathepsin G. Kinetic analysis of the reactions with uPA, tPA, plasmin, thrombin, Xa, and C1s showed second- order rate constants to vary over 3 logs, from k(inh) = 3 x 105 M-1 s-1 with thrombin to ~600 M-1 s-1 with C1s, while steady-state inhibition constants ranged from K(I) = 10 pM with thrombin to ~100 nM with C1s. Stoichiometries of inhibition varied between SI = 1.4 ± 0.1 for uPA to SI = 13 ± 3 for thrombin. Analysis of the variations in inhibition kinetics shows that when serpins act at low concentrations, comparable with the target protease or with K(I) (as appears likely for SERP-1 in vivo), inhibitory specificity becomes less dominated by k(inh) and is increasingly dependent on partitioning within the branched reaction mechanism and on the lifetime of the inhibited complex.

Original languageEnglish (US)
Pages (from-to)20982-20991
Number of pages10
JournalJournal of Biological Chemistry
Issue number33
StatePublished - Aug 14 1998
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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