1I4E: Crystal Structure Of The Caspase-8/p35 Complex

Apoptosis is a highly regulated process that is crucial for normal development and homeostasis of multicellular organisms. The p35 protein from baculoviruses effectively prevents apoptosis by its broad-spectrum caspase inhibition. Here we report the crystal structure of p35 in complex with human caspase-8 at 3.0 A resolution, and biochemical and mutagenesis studies based on the structural information. The structure reveals that the caspase is inhibited in the active site through a covalent thioester linkage to p35, which we confirmed by gel electrophoresis, hydroxylamine treatment and mass spectrometry experiments. The p35 protein undergoes dramatic conformational changes on cleavage by the caspase. The repositioning of the amino terminus of p35 into the active site of the caspase eliminates solvent accessibility of the catalytic dyad. This may be crucial for preventing hydrolysis of the thioester intermediate, which is supported by the abrogation of inhibitory activity through mutations at the N terminus of p35. The p35 protein also makes conserved contacts with the caspase outside the active-site region, providing the molecular basis for the broad-spectrum inhibitory activity of this protein. We demonstrate a new molecular mechanism of caspase inhibition, as well as protease inhibition in general.
PDB ID: 1I4EDownload
MMDB ID: 82395
PDB Deposition Date: 2001/2/20
Updated in MMDB: 2013/09
Experimental Method:
x-ray diffraction
Resolution: 3  Å
Source Organism:
Autographa californica nucleopolyhedrovirus
Similar Structures:
Biological Unit for 1I4E: dimeric; determined by author and by software (PISA)
Molecular Components in 1I4E
Label Count Molecule
Proteins (2 molecules)
Early 35 KDA Protein(Gene symbol: Ac-35K/p35)
Molecule annotation
Caspase-8(Gene symbol: CASP8)
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB