Family C71


Summary Holotypes Alignment Genomes Literature

Summary for family C71

Family type peptidaseC71.001 - pseudomurein endoisopeptidase Pei (Methanobacterium phage psiM2), MEROPS Accession MER0019309 (peptidase unit: 157-305)
Content of familyPeptidase family C71 contains endopeptidases that cleave crosslinking peptides of the archaean cell wall.
History Identifier created: MEROPS 6.9 (16 December 2004)
The cell walls of archaea are very varied in nature. That of Methanothermobacter is analogous to that of a bacterium, with parallel chains of a glycoprotein, pseudomurein, crosslinked by a peptide. Pseudomurein is a polymer of N-acetyl-L-talosaminurinic acid, whereas murein is a polymer of N-acetyl-D-muramic acid). The crosslinking peptide contains only amino acids in the normal, laevo, orientation, unlike those of bacteria. The cross-link is made between the epsilon-amino group of L-Lys and the alpha-carbonyl group of L-Ala (Kiener et al., 1987). Archaea are infected by phages, and mature phage particles have to lyse the cell walls to escape the host. Family U64 contains the pseudomurein endoisopeptidase that cleaves the archaean cell wall crosslinks.
Catalytic typeCysteine
Active site residuesC213 H248 D272 
Active siteAlthough the catalytic type has not been biochemically characterized, a catalytic triad consisting of Cys213, His248 and Asp272 (see the Alignment) has been proposed (Makarova et al., 1999, Luo et al., 2002), implying that the enzymes are cysteine peptidases. The active site His occurs in a Gly-His-Tyr motif that also occurs in family C19.
Activities and specificitiesThe crosslinking peptide is cleaved at the the ε-amino group of L-Lys and the α-carbonyl group of L-Ala. This is an isopeptide bond, hence the enzyme is known as an 'endoisopeptidase' (Kiener et al., 1987). The enzyme is very active at high temperatures (e.g. 62 degrees Celsius), and has a broad pH optimum (Stax et al., 1992.
InhibitorsActivity is destroyed by exposure to oxygen (Kiener et al., 1987).
Molecular structureAlthough no tertiary structure has been solved, from the order of the predicted active site residues, family C71 is included in clan CA.
Distribution of family Bacteria -  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals -  
Viruses details  
Biological functionsThe pseudomurein endoisopeptidase is encoded by a phage, but the genome of Methanothermobacter wolfeii contains a defective prophage that carries an active copy of the gene for the endoisopeptidase (Luo et al., 2001. This may explain why the enzyme can be isolated from uninfected as well as infected archaea.
Statistics for family C71Sequences:2
Identifiers with PDB entries:0
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Peptidases and Homologues MEROPS ID Structure
pseudomurein endoisopeptidase PeiC71.001-
family C71 unassigned peptidasesunassigned-