Caspase-1

 

Caspases are thiol endopeptidases that cleave specific proteins after Asp residues and drive apoptosis or inflammation. Caspase-1 is part of the family of inflammatory-caspases, which also includes caspase-4 and caspase-5 in humans and caspase-11, -12, -13 and -14 in mice. Activation of caspase-1 requires oligomerisation of inactive monomeric proenzyme forms. Caspase-1 has a recognition site of Tyr-Val-Ala-Asp-|-. Caspase-1 is also known as interleukin converting enzyme (ICE) and cleaves precursors of the inflammatory interleukin1β and interleukin18 which converts them into mature, active peptides which can initiate a proinflammatory pathway. These often contribute to the pathophysioiogy of many inflammatory and autoimmune diseases, including septic shock, rheumatoid arthritis, and insulin-dependent diabetes mellitus.

 

Reference Protein and Structure

Sequence
P29466 UniProt (3.4.22.36) IPR015917 (Sequence Homologues) (PDB Homologues)
Biological species
Homo sapiens (Human) Uniprot
PDB
2fqq - Crystal structure of human caspase-1 (Cys285->Ala, Cys362->Ala, Cys364->Ala, Cys397->Ala) in complex with 1-methyl-3-trifluoromethyl-1H-thieno[2,3-c]pyrazole-5-carboxylic acid (2-mercapto-ethyl)-amide (3.3 Å) PDBe PDBsum 2fqq
Catalytic CATH Domains
3.30.70.1470 CATHdb 3.40.50.1460 CATHdb (see all for 2fqq)
Click To Show Structure

Enzyme Reaction (EC:3.4.22.36)

Asp-Gly
CHEBI:73450ChEBI
+
water
CHEBI:15377ChEBI
→
L-aspartic acid
CHEBI:17053ChEBI
+
glycine
CHEBI:15428ChEBI
Alternative enzyme names: ICE, Interleukin 1 converting enzyme, Interleukin 1-beta precursor proteinase, Interleukin 1-beta-converting endopeptidase, Interleukin 1-beta-converting enzyme, Interleukin-1-beta convertase, Interleukin-1-beta converting enzyme, Interleukin-1-beta precursor proteinase, Precursor interleukin-1-beta converting enzyme, Pro-interleukin 1-beta proteinase, Prointerleukin 1-beta protease, Protease A, Protease VII, Interleukin-1 beta convertase precursor, Interleukin 1-beta converting enzyme,

Enzyme Mechanism

Introduction

During the acylaton step, the carbonyl oxygen of the non-covalently bonded P1 (usually Asp) residue is anchored through hydrogen bonds to the backbone nitrogen atoms of Gly238 and Cys285 which from the oxyanion hole. This increases the polarisation of the C-O bond and therefore facilitates nucleophilic attack of the S atom of Cys285 on the highly electrophilic carbonyl carbon. The result is a covalent enzyme-substrate adduct - high energy tetrahedral intermediate. The imidazole moiety of His237 acts as a general acid by protonating the alpha-amino group of the leaving peptide product, thus avoiding re-formation of the peptide bond. Deacylation of the acyl-enzyme complex occurs in a similar way. The deprotonatad His237 side chain abstracts a proton from a water molecule, activating it as a nucleophile to attack the carbonyl carbon of the thioester bond, forming a second tetrahedral intermediate. Rupture of the S-C bond regenerates the enzyme in a non-covalent complex with the N-terminal peptide product.

Catalytic Residues Roles

UniProt PDB* (2fqq)
Cys285 (main-N), Cys285 Ala285(166)A (main-N), Ala285(166)A Cys285 backbone N forms part of the oxyanion hole which is involved in increasing the electrophicity of the taget carbon. Cys285 also acts as a nucleophile in the acylation step, attacking the electrophilic carbonyl carbon of the substrate. electrostatic stabiliser
Arg286 Arg286(167)A Works together with Glu290 to stabilise the transition state intermediate. electrostatic stabiliser
Gly238 (main-N) Gly238(119)A (main-N) The backbone N of this residue forms part of te oxyanion hole with Cys285. electrostatic stabiliser
His237 His237(118)A His237 activates water by proton abstraction to perform nucleophilic attack on the thioester bond of the acyl-enzyme intermediate in the deacylation step. The His237 delta-N atom is also involved in stabilising the leaving group to prevent peptide re-formation. proton acceptor, proton donor
Glu390 Glu390(74)B Glu390 works with Arg286 to stabilise the transition state intermediate together. electrostatic stabiliser
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file; y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain; C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.

Chemical Components

proton transfer, bimolecular nucleophilic addition, intermediate formation, overall reactant used, unimolecular elimination by the conjugate base, heterolysis, intermediate collapse, overall product formed, native state of enzyme regenerated

References

  1. Scheer JM et al. (2006), Proc Natl Acad Sci U S A, 103, 7595-7600. A common allosteric site and mechanism in caspases. DOI:10.1073/pnas.0602571103. PMID:16682620.
  2. Wilson KP et al. (1994), Nature, 370, 270-275. Structure and mechanism of interleukin-lβ converting enzyme. DOI:10.1038/370270a0. PMID:8035875.
  3. Walker NP et al. (1994), Cell, 78, 343-352. Crystal structure of the cysteine protease interleukin-1β-converting enzyme: A (p20/p10)2 homodimer. DOI:10.1016/0092-8674(94)90303-4. PMID:8044845.

Step 1. His237 deprotonates Cys55 which activates it to attack the carbonyl group of the peptide bond by nucleophilic addition which produces the oxyanion intermediate.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Arg286(167)A electrostatic stabiliser
Gly238(119)A (main-N) electrostatic stabiliser
Glu390(74)B electrostatic stabiliser
Ala285(166)A (main-N) electrostatic stabiliser
His237(118)A proton acceptor
Ala285(166)A proton donor, nucleophile

Chemical Components

proton transfer, ingold: bimolecular nucleophilic addition, intermediate formation, overall reactant used

Step 2. The oxyanion initiates an elimantion resulting in the cleavage of the peptide bond, the N-terminal product then accepts a proton from His237.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Gly238(119)A (main-N) electrostatic stabiliser
Ala285(166)A (main-N) electrostatic stabiliser
Arg286(167)A electrostatic stabiliser
Glu390(74)B electrostatic stabiliser
His237(118)A proton donor

Chemical Components

proton transfer, ingold: unimolecular elimination by the conjugate base, heterolysis, intermediate collapse, overall product formed

Step 3. His237 deprotonates water activating it to attack the carbon of the carbonyl carbon of the thioester bond by nucleophilic addition.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Gly238(119)A (main-N) electrostatic stabiliser
Ala285(166)A (main-N) electrostatic stabiliser
Arg286(167)A electrostatic stabiliser
Glu390(74)B electrostatic stabiliser
His237(118)A proton acceptor

Chemical Components

proton transfer, ingold: bimolecular nucleophilic addition, intermediate formation, overall reactant used

Step 4. The oxyanion initiates an elimination which results in the cleavage of the thioester bond and thus releasing the C-terminal product. Cys285 will then accept a proton from His237 returning the enzyme to its native state.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Gly238(119)A (main-N) electrostatic stabiliser
Ala285(166)A (main-N) electrostatic stabiliser
Arg286(167)A electrostatic stabiliser
Glu390(74)B electrostatic stabiliser
His237(118)A proton donor
Ala285(166)A proton acceptor, nucleofuge

Chemical Components

ingold: unimolecular elimination by the conjugate base, heterolysis, proton transfer, intermediate collapse, native state of enzyme regenerated, overall product formed
Download: Image, Marvin File

Step 1. His237 deprotonates Cys55 which activates it to attack the carbonyl group of the peptide bond by nucleophilic addition which produces the oxyanion intermediate.

Step 2. The oxyanion initiates an elimantion resulting in the cleavage of the peptide bond, the N-terminal product then accepts a proton from His237.

Step 3. His237 deprotonates water activating it to attack the carbon of the carbonyl carbon of the thioester bond by nucleophilic addition.

Step 4. The oxyanion initiates an elimination which results in the cleavage of the thioester bond and thus releasing the C-terminal product. Cys285 will then accept a proton from His237 returning the enzyme to its native state.

Products.

Contributors

Gemma L. Holliday, Charity Hornby