Tricorn protease

 

The tricorn protease is the core of a proteolytic system identified in the model organism Thermoplasma acidophilum. This complex functions to degrade the 7-9 residue peptides that are produced by the proteasome-mediated degradation of cellular proteins. The basic functional unit of the tricorn protease is a homohexamer of the 121 kDa subunit; however electron microscopy studies indicate that 20 copies of this 720 kDa hexamer can assemble further in vivo to form a giant 14.6 MDa icosahedral capsid.

 

Reference Protein and Structure

Sequence
P96086 UniProt (3.4.21.-) IPR012393 (Sequence Homologues) (PDB Homologues)
Biological species
Thermoplasma acidophilum DSM 1728 (Archaea) Uniprot
PDB
1k32 - Crystal structure of the tricorn protease (2.0 Å) PDBe PDBsum 1k32
Catalytic CATH Domains
3.90.226.10 CATHdb 3.30.750.44 CATHdb (see all for 1k32)
Click To Show Structure

Enzyme Reaction (EC:3.4.21.-)

water
CHEBI:15377ChEBI
+
dipeptide
CHEBI:46761ChEBI
→
L-alpha-amino acid
CHEBI:15705ChEBI

Enzyme Mechanism

Introduction

The tricorn protease is thought to use a mechanism similar to that of the trypsin-like serine proteases. His 746 deprotonates Ser 965 which attacks the peptide bond to form a tetrahedral intermediate. Accumulation of negative charge on the carbonyl oxygen during formation of the tetrahedral intermediate is stabilised by an oxyanion hole composed of the backbone NH groups of Gly 918 and Asp 966. Collapse of the tetrahedral intermediate with protonation of the departing leaving group by His 746 generates and acyl-enzyme intermediate; this is subsequently hydrolysed by a water molecule that is deprotonated by His 746.

Catalytic Residues Roles

UniProt PDB* (1k32)
Gly918 (main-N), Asp966 (main-N) Gly918(892)A (main-N), Asp966(940)A (main-N) Backbone NH forms part of the oxyanion hole that stabilises the tetrahedral intermediate. electrostatic stabiliser
Ser965 Ser965(939)A Acts as a nucleophile to attack the peptide bond and form an acyl-enzyme intermediate which is subsequently hydrolysed. covalently attached
His746 His746(720)A Deprotonates Ser 965. Protonates the departing amine nitrogen during collapse of the tetrahedral intermediate. Deprotonates the water molecule that hydrolyses the acyl-enzyme intermediate. proton shuttle (general acid/base)
*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

References

  1. Brandstetter H et al. (2001), Nature, 414, 466-470. Crystal structure of the tricorn protease reveals a protein disassembly line. DOI:10.1038/35106609. PMID:11719810.

Step 1.

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Catalytic Residues Roles

Residue Roles
Ser965(939)A covalently attached
His746(720)A proton shuttle (general acid/base)
Asp966(940)A (main-N) electrostatic stabiliser
Gly918(892)A (main-N) electrostatic stabiliser

Chemical Components

Step 1.

Contributors

Steven Smith, Gemma L. Holliday