Novel mechanism of bacteriocin secretion and immunity carried out by lactococcal multidrug resistance proteins.
A natural isolate of Lactococcus lactis was shown to produce two narrow spectrum class II bacteriocins, designated LsbA and LsbB. The cognate genes are located on a 5.6-kb plasmid within a gene cluster specifying LmrB, an ATP-binding cassette-type multidrug resistance transporter protein. LsbA is a hydrophobic peptide that is initially synthesized with an N-terminal extension. The housekeeping surface proteinase HtrA was shown to be responsible for the cleavage of precursor peptide to yield the active bacteriocin. LsbB is a relatively hydrophilic protein synthesized without an N-terminal leader sequence or signal peptide. The secretion of both polypeptides was shown to be mediated by LmrB. An L. lactis strain lacking plasmid-encoded LmrB and the chromosomally encoded LmrA is unable to secrete either of the two bacteriocins. Complementation of the strain with an active LmrB protein resulted in restored export of the two polypeptides across the cytoplasmic membrane. When expressed in an L. lactis strain that is sensitive to LsbA and LsbB, LmrB was shown to confer resistance toward both bacteriocins. It does so, most likely, by removing the two polypeptides from the cytoplasmic membrane. This is the first report in which a multidrug transporter protein is shown to be involved in both secretion and immunity of antimicrobial peptides.
Gajic
Olivera
O
Department of Genetics, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands.
Buist
Girbe
G
Kojic
Milan
M
Topisirovic
Ljubisa
L
Kuipers
Oscar P
OP
Kok
Jan
J
D000595:Amino Acid Sequence; D001430:Bacteriocins / Q000235:genetics* / Q000378:metabolism*; D015152:Blotting, Northern; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D018432:Drug Resistance, Multiple; D004591:Electrophoresis, Polyacrylamide Gel; D017353:Gene Deletion; D049452:Green Fluorescent Proteins; D017045:Lactococcus / Q000378:metabolism*; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D008969:Molecular Sequence Data; D005810:Multigene Family; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000378:metabolism
D001430:Bacteriocins; D017931:DNA Primers; D008164:Luminescent Proteins; D010455:Peptides; D012333:RNA, Messenger; D049452:Green Fluorescent Proteins; D004247:DNA; D001616:beta-Galactosidase