Dysgalacticin: a novel, plasmid-encoded antimicrobial protein (bacteriocin) produced by Streptococcus dysgalactiae subsp. equisimilis.
Dysgalacticin is a novel bacteriocin produced by Streptococcus dysgalactiae subsp. equisimilis strain W2580 that has a narrow spectrum of antimicrobial activity directed primarily against the principal human streptococcal pathogen Streptococcus pyogenes. Unlike many previously described bacteriocins of Gram-positive bacteria, dysgalacticin is a heat-labile 21.5 kDa anionic protein that kills its target without inducing lysis. The N-terminal amino acid sequence of dysgalacticin [Asn-Glu-Thr-Asn-Asn-Phe-Ala-Glu-Thr-Gln-Lys-Glu-Ile-Thr-Thr-Asn-(Asn)-Glu-Ala] has no known homologue in publicly available sequence databases. The dysgalacticin structural gene, dysA, is located on the indigenous plasmid pW2580 of strain W2580 and encodes a 220 aa preprotein which is probably exported via a Sec-dependent transport system. Natural dysA variants containing conservative amino acid substitutions were also detected by sequence analyses of dysA elements from S. dysgalactiae strains displaying W2580-like inhibitory profiles. Production of recombinant dysgalacticin by Escherichia coli confirmed that this protein is solely responsible for the inhibitory activity exhibited by strain W2580. A combination of in silico secondary structure prediction and reductive alkylation was employed to demonstrate that dysgalacticin has a novel structure containing a disulphide bond essential for its biological activity. Moreover, dysgalacticin displays similarity in predicted secondary structure (but not primary amino acid sequence or inhibitory spectrum) with another plasmid-encoded streptococcal bacteriocin, streptococcin A-M57 from S. pyogenes, indicating that dysgalacticin represents a prototype of a new class of antimicrobial proteins.
Heng
Nicholas C K
NCK
Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin, New Zealand.
Ragland
Nancy L
NL
Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin, New Zealand.
Swe
Pearl M
PM
Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin, New Zealand.
Baird
Hayley J
HJ
Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin, New Zealand.
Inglis
Megan A
MA
Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin, New Zealand.
Tagg
John R
JR
Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin, New Zealand.
Jack
Ralph W
RW
Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin, New Zealand.
D000595:Amino Acid Sequence; D001430:Bacteriocins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D001483:Base Sequence; D004220:Disulfides / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics; D008969:Molecular Sequence Data; D010957:Plasmids; D011994:Recombinant Proteins / Q000096:biosynthesis; D013291:Streptococcus / Q000378:metabolism*
D001430:Bacteriocins; D004220:Disulfides; D011994:Recombinant Proteins