Serum opacity factor promotes group A streptococcal epithelial cell invasion and virulence.
Serum opacity factor (SOF) is a bifunctional cell surface protein expressed by 40-50% of group A streptococcal (GAS) strains comprised of a C-terminal domain that binds fibronectin and an N-terminal domain that mediates opacification of mammalian sera. The sof gene was recently discovered to be cotranscribed in a two-gene operon with a gene encoding another fibronectin-binding protein, sfbX. We compared the ability of a SOF(+) wild-type serotype M49 GAS strain and isogenic mutants lacking SOF or SfbX to invade cultured HEp-2 human pharyngeal epithelial cells. Elimination of SOF led to a significant decrease in HEp-2 intracellular invasion while loss of SfbX had minimal effect. The hypoinvasive phenotype of the SOF(-) mutant could be restored upon complementation with the sof gene on a plasmid vector, and heterologous expression of sof49 in M1 GAS or Lactococcus lactis conferred marked increases in HEp-2 cell invasion. Studies using a mutant sof49 gene lacking the fibronectin-binding domain indicated that the N-terminal opacification domain of SOF contributes to HEp-2 invasion independent of the C-terminal fibronectin binding domain, findings corroborated by observations that a purified SOF N-terminal peptide could promote latex bead adherence to HEp-2 cells and inhibit GAS invasion of HEp-2 cells in a dose-dependent manner. Finally, the first in vivo studies to employ a single gene allelic replacement mutant of SOF demonstrate that this protein contributes to GAS virulence in a murine model of necrotizing skin infection.
Timmer
Anjuli M
AM
Department of Pediatrics, Division of Pharmacology and Drug Discovery, University of California, San Diego, La Jolla, CA, USA.
Kristian
Sascha A
SA
Datta
Vivekanand
V
Jeng
Arthur
A
Gillen
Christine M
CM
Walker
Mark J
MJ
Beall
Bernard
B
Nizet
Victor
V
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism* / Q000382:microbiology; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D051379:Mice; D009154:Mutation / Q000235:genetics; D010447:Peptide Hydrolases / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D013297:Streptococcus pyogenes / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D014774:Virulence / Q000235:genetics
D001426:Bacterial Proteins; D002352:Carrier Proteins; D005353:Fibronectins; D047908:Intracellular Signaling Peptides and Proteins; C471999:SfbX protein, Streptococcus pyogenes; C021908:opacity factor; D010447:Peptide Hydrolases