Peptidase A24A, prepilin type IV, bacterial (IPR014032)

Short name: Peptidase_A24A_bac

Overlapping homologous superfamilies


Family relationships



Cysteine protease activity is dependent on an active dyad of cysteine and histidine, the order and spacing of these residues varying in the 20 or so known families. Cysteine proteases have been grouped into two clans (CA and CB). Families C1, C2 and C10 are loosely termed papain-like and belong to clan CA; five cysteine proteases belong to clan CB; other families have not been assigned to clans. Nearly half of all cysteine proteases are found exclusively in viruses. The order of catalytic cysteine and histidine residues within the primary structure differs between the families and is an indication of convergent evolution [PMID: 7845226, PMID: 8439290].

Bacteria produce a number of protein precursors that undergo post- translational methylation and proteolysis prior to secretion as active proteins. Type IV prepilin leader peptidases, which belong to the C20 family of cysteine proteases, are enzymes that mediate this type of post- translational modification. Type IV pilin is a protein found on the surface of Pseudomonas aeruginosa, Neisseria gonorrhoeae and other Gram-negative pathogens. Pilin subunits attach the infecting organism to the surface of host epithelial cells. They are synthesised as prepilin subunits, which differ from mature pilin by virtue of containing a 6-8 residue leader peptide consisting of charged amino acids. Mature type IV pilins also contain a methylated N-terminal phenylalanine residue.

Prepilin leader peptidases are found on the cytosolic membrane surface, where they have dual activity, involving cleavage of glycine-phenylalanine bonds and methylation of the newly-revealed N-terminal phenylalanine. The consensus sequence for the site of proteolytic cleavage is -G+F-T-L/I-, in which the Gly P1 residue is essential [PMID: 7845226]. The peptidases are suseptible to thiol blocking reagents. Site directed mutagenesis has indicated four highly conserved cysteine residues that affect both the protease and methylase activity.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.