Crystal structure of the apoptotic suppressor CrmA in its cleaved form

Structure. 2000 Jul 15;8(7):789-97. doi: 10.1016/s0969-2126(00)00165-9.


Background: Cowpox virus expresses the serpin CrmA (cytokine response modifier A) in order to avoid inflammatory and apoptotic responses of infected host cells. The targets of CrmA are members of the caspase family of proteases that either initiate the extrinsic pathway of apoptosis (caspases 8 and 10) or trigger activation of the pro-inflammatory cytokines interleukin-1beta and interleukin-18 (caspase 1).

Results: We have determined the structure of a cleaved form of CrmA to 2.26 A resolution. CrmA has the typical fold of a cleaved serpin, even though it lacks the N-terminal half of the A helix, the entire D helix, and a portion of the E helix that are present in all other known serpins. The reactive-site loop of CrmA was mutated to contain the optimal substrate recognition sequence for caspase 3; however, the mutation only marginally increased the ability of CrmA to inhibit caspase 3. Superposition of the reactive-site loop of alpha1-proteinase inhibitor on the cleaved CrmA structure provides a model for virgin CrmA that can be docked to caspase 1, but not to caspase 3.

Conclusions: CrmA exemplifies viral economy, selective pressure having resulted in a 'minimal' serpin that lacks the regions not needed for structural integrity or inhibitory activity. The docking model provides an explanation for the selectivity of CrmA. Our demonstration that engineering optimal substrate recognition sequences into the CrmA reactive-site loop fails to generate a good caspase 3 inhibitor is consistent with the docking model.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Apoptosis / drug effects*
  • Caspases / metabolism
  • Cowpox virus / chemistry*
  • Crystallography, X-Ray
  • Cysteine Proteinase Inhibitors / chemistry
  • Cysteine Proteinase Inhibitors / metabolism
  • Humans
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Conformation
  • Sequence Alignment
  • Sequence Deletion
  • Sequence Homology, Amino Acid
  • Serine Endopeptidases / metabolism
  • Serpins / chemistry*
  • Serpins / genetics
  • Serpins / pharmacology
  • Structure-Activity Relationship
  • Substrate Specificity
  • Subtilisin / metabolism
  • Viral Proteins / chemistry*
  • Viral Proteins / genetics
  • Viral Proteins / pharmacology


  • Cysteine Proteinase Inhibitors
  • Serpins
  • Viral Proteins
  • interleukin-1beta-converting enzyme inhibitor
  • Serine Endopeptidases
  • Subtilisin
  • Caspases

Associated data

  • PDB/1F0C