Inhibition of interleukin-1 beta converting enzyme by the cowpox virus serpin CrmA. An example of cross-class inhibition.
We reported previously that human interleukin-1 beta converting enzyme (ICE) is regulated by the CrmA serpin encoded by cowpox virus. We now report the mechanism and kinetics of this unusual inhibition of a cysteine proteinase by a member of the serpin superfamily previously thought to inhibit serine proteinase only. CrmA possesses several characteristics typical of a number of inhibitory serpins. It is conformationally unstable, unfolding around 3 M urea, and stable to denaturation in 8 M urea upon complex formation with ICE. CrmA rapidly inhibits ICE with an association rate constant (kon) of 1.7 x 10(7) M-1 s-1, forming a tight complex with an equilibrium constant for inhibition (Ki) of less than 4 x 10(-12) M. These data indicate that CrmA is a potent inhibitor of ICE, consistent with the dramatic effects of CrmA on modifying host responses to virus infection. The inhibition of ICE by CrmA is an example of a "cross-class" interaction, in which a serpin inhibits a non-serine proteinase. Since CrmA possesses characteristics shared by inhibitors of serine proteinases, we presume that ICE, though it is a cysteine proteinase, has a substrate binding geometry strikingly close to that of serine proteinases. We reason that it is the substrate binding geometry, not the catalytic mechanism of a proteinase, that dictates its reactivity with protein inhibitors.
Komiyama
T
T
Department of Pathology, Duke University Medical Center, Durham, North Carolina 27710.
Ray
C A
CA
Pickup
D J
DJ
Howard
A D
AD
Thornberry
N A
NA
Peterson
E P
EP
Salvesen
G
G
D000595:Amino Acid Sequence; D020170:Caspase 1; D015608:Cowpox virus / Q000201:enzymology*; D003546:Cysteine Endopeptidases / Q000145:classification / Q000378:metabolism; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008666:Metalloendopeptidases / Q000378:metabolism*; D008969:Molecular Sequence Data; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012697:Serine Endopeptidases / Q000378:metabolism; D015843:Serpins / Q000378:metabolism*; D014764:Viral Proteins
D011993:Recombinant Fusion Proteins; D015843:Serpins; D014764:Viral Proteins; C074641:interleukin-1beta-converting enzyme inhibitor; D005982:Glutathione Transferase; D012697:Serine Endopeptidases; D003546:Cysteine Endopeptidases; D020170:Caspase 1; D008666:Metalloendopeptidases