| Type: | Family | Name: | Peptidase C56, PfpI |
| Description: | Cysteine peptidases have characteristic molecular topologies, which can be seen not only in their three-dimensional structures, but commonly also in the two-dimensional structures. These are peptidases in which the nucleophile is the sulphydryl group of a cysteine residue. Cysteine proteases are divided into clans (proteins which are evolutionary related), and further sub-divided into families, on the basis of the architecture of their catalytic dyad or triad []. This group of cysteine peptidases form part of the MEROPS peptidase family C56 (Pfp1 endopeptidase, clan PC(C)).The best characterised protein in this entry, Pyrococcus furiosusprotease I (PfpI), is an intracellular cysteine peptidase characterised by its stability and proposed to represent the predominant proteolytic activity of this thermophilic archaebacterium. Pfpi-like proteins have been found in bacteria, archaea, in some plants and in amoebae. The structure of P. horikoshii PfpI shows an alpha/beta sandwich fold, which consists of a central beta sheet flanked by two helices and two strands on one side, and by six helices and two strands on the other side. The fold resembles that of glutamine amidotransferases (GATase) of class I, which are characterised by a conserved Cys-His-Glu active site. The catalytically essential cysteine is located at a nucleophile elbow. PfpI forms a hexameric structure and the active sites are formed at the interfaces between three pairs of monomers. Cys and His form a triad with a glutamate residue from an adjacent monomer [].Peptidase C56 family proteins not found in this entry are structurally and functionally different [], e.g. human DJ-1 creates a hydrophobic patch at the molecular interface instead of completing the catalytic triad, while Escherichia colichaperone HSP31 forms a Cys-His-Asp triad.Some proteins known to contain a PfpI endopeptidase domain: P. furiosus intracellular protease 1 (PfpI), an ATP-independent, highly thermically and chemically stable endopeptidase.Pyrococcus horikoshiiintracellular protease 1 (PfpI/PH1704).Bacillus subtilisgeneral stress protein 18 (GSP18).E. coli protein yhbO. | Short Name: | Peptidase_C56 |
