|Family type peptidase||C96.001 - McjB peptidase (Escherichia coli), MEROPS Accession MER0183786 (peptidase unit: 143-208)|
|Content of family||Peptidase family C96 contains cysteine type endopeptidases.|
Identifier created: MEROPS 9.6 (29 February 2012)|
Microcin J25 is a peptide antibiotic that inhibits DNA-dependent RNA polymerase. It is synthesized as a precursor by Escherichia coli and secreted as an antibacterial agent against members of the Enterbacteriaceae. The microcin gene is on plasmid pTUC100 and is part of an operon with four genes, one of which, mcjB, encodes the peptidase responsible for the activation of the microcin (Solbiati et al., 1999).
|Active site residues||C150 H182 D194 |
|Active site||A catalytic triad comprising Cys, His and Asp has been proposed from comparison with the active site residues of other members of clan CA (Makarova et al., 1999. Site-directed mutagenesis have confirmed that Cys150 and His182 are essential for activity. However, what is the third member of the catalytic triad is open to question, because mutants with Glu186 replaced are proteolytically inactive, whereas replacement of Asp194 reduces activity but does not abolish it (<%Yan et al., 2012%>).|
|Activities and specificities||McjB removes the leader peptide of microcin J25, which is the first of two events that are required for the maturation of microcin J25 into a cyclic peptide (its 'lasso conformation'). The cleavage occurs at Thr36-Lys+Glu, and Thr36 and Glu38 are essential because mutants in which these are replaced are poorly cleaved (<%Yan et al., 2012%>).
|Molecular structure||Members of family C96 were identified as distant homologues of eukaryotic transglutaminases (Makarova et al., 1999), which have structures that are related to that of papain (C01.001). For this reason, family C96 is included in clan CA, despite the lack of tertiary structural data for any member of family C96.|