Family C75


Summary Holotypes Alignment Tree Genomes Literature

Summary for family C75

Family type peptidaseC75.001 - AgrB peptidase (Staphylococcus aureus), MEROPS Accession MER0043287 (peptidase unit: 1-189)
Content of familyPeptidase family C75 contains endopeptidases.
History Identifier created: MEROPS 8.0 (8 January 2008)
The operon of the accessory gene regulator (agr) of Staphylococcus aureus encodes four genes (agrA, B, C, and D) whose products compose a quorum sensing system. AgrA and AgrC resemble a two-component signal-transduction system of which AgrC is a sensor kinase and AgrA is a response regulator. AgrD is a polypeptide that is integrated into the cytoplasmic membrane via its N-terminal region, and is the precursor for an autoinducing peptide (AIP) that is the ligand for AgrC. Zhang et al. (2002) speculated that AgrB is a proteolytic enzyme responsible for the processing of AgrD to liberate the AIP, and this has been confirmed by later work (Qiu et al. (2005); Kavanaugh et al., 2007). .
Catalytic typeCysteine
Active site residuesH77 C84 
Active siteThe catalytic residues identified in Staphylococcus aureus AgrB by Qiu et al. (2005) are His77 and Cys84.
Activities and specificitiesThe AIP is derived from the central region of the AgrD sequence, so the processing involves removal of both N-terminal and C-terminal extensions. AgrB cleaves off the C-terminus, and the N-terminus is cleaved by the signal peptidase, SpsB (S26.016) (Kavanaugh et al., 2007).
InhibitorsInhibition was observed with several peptidyl chloromethanes, but not E64 (Qiu et al., 2005).
Molecular structureAgrB is an integral membrane protein. No three-dimensional structure is available, but the way in which it may be inserted into the bacterial membrane has been described by Zhang & Ji (2004). This model places the active site residues in or close to the cytoplasm.
Distribution of family Bacteria details  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals -  
Viruses -  
Biological functionsThe peptidases in family C75 contribute to the synthesis of bacterial autoinducing peptides by cleavage of precursor proteins (Qiu et al. (2005); Kavanaugh et al., 2007).
Statistics for family C75Sequences:119
Identifiers with PDB entries:0
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Peptidases and Homologues MEROPS ID Structure
AgrB peptidaseC75.001-
FsrB peptidase (Enterococcus faecalis)C75.002-
family C75 non-peptidase homologuesnon-peptidase homologue-
family C75 unassigned peptidasesunassigned-