A FAMILY OF BACTERIOCIN ABC TRANSPORTERS CARRY OUT PROTEOLYTIC PROCESSING OF THEIR SUBSTRATES CONCOMITANT WITH EXPORT

Lantibiotic and non-lantibiotic bacteriocins are synthesized as precur sor peptides containing N-terminal extensions (leader peptides) which are cleaved off during maturation. Most non-lantibiotics and also some lantibiotics have leader peptides of the so-called double-glycine typ e. These leader peptides share consensus sequences and also a common p rocessing site with two conserved glycine residues in positions -1 and -2. The double-glycine-type leader peptides are unrelated to the N-te rminal signal sequences which direct proteins across the cytoplasmic m embrane via the sec pathway. Their processing sites are also different from typical signal peptidase cleavage sites, suggesting that a diffe rent processing enzyme is involved. Peptide bacteriocins are exported across the cytoplasmic membrane by a dedicated ATP-binding cassette (A BC) transporter. Here we show that the ABC transporter is the maturati on protease and that its proteolytic domain resides in the N-terminal part of the protein. This result demonstrates that the ABC transporter has a dual function: (i) removal of the leader peptide from its subst rate, and (ii) translocation of its substrate across the cytoplasmic m embrane. This represents a novel strategy for secretion of bacterial p roteins.