PROSITE documentation PDOC50990

Peptidase family C39 domain profile

ABC transporters belong to the ATP-Binding Cassette (ABC) superfamily which uses the hydrolysis of ATP to energize diverse biological import and export systems (see <PDOC00185>). ABC transporters are constituted at least of two conserved regions: a highly conserved ATP binding cassette (ABC) and a less conserved transmembrane domain (TMD) (see <PDOC00364>). These regions can be found on the same protein (mostly bacterial exporters and eukaryotes) or on two different ones (mostly bacterial importers) [1,2,3]. Nevertheless, in a wide range of ABC exporters, an additional protease domain of about 130 amino acid residues is found to be fused to the TMD and the NBD. This domain is a maturation protease for certain peptide bacteriocins, namely those containing the double glycine leader motif. These include class II bacteriocins of Gram-positive and Gram-negative bacteria, as well as some of the lantibiotics, the CSPs (competence stimulating peptide) and peptides pheromones. The proteolytic domain reside in the N-terminal region of the protein. It is a thiol peptidase and belongs to the C39 peptidase family [E1].

Thus all bacteriocin precursors containing double-glycine-type leader peptides are processed and export concomitantly by a proteolytic domain residing in the N-termini of their dedicated ABC transporter. It appears that this kind of processing is more efficient [4,5]. It results in cleavage and translocation of both peptides simultaneously, probably by processing the signal peptide and exporting the resulting mature lantibiotic. A number of the proteins are classified as non-peptidase homologues as they either have been found experimentally to be without peptidase activity, or to lack amino acid residues that are believed to be essential for the catalytic activity. Even though these domains have lost their proteolytic properties they still serve as substrate-recognition domains [6].

All different types of transporters containing an ABC peptidase domain are listed below (references are only provided for recently characterized proteins) [E2].

• Lantibiotic exporter: hemolysin/bacteriocin (cylB).
• Micrococin B17 exporter (mcbF).
• Peptide-2 exporter: competence factor (comA/comB).
• Protein-1 exporter: hemolysin (hlyB).
• Protein-2 exporter: colicin V(cvaB).
• Pediocin exporter (pedD).