SIC, a secreted protein of Streptococcus pyogenes that inactivates antibacterial peptides.
Frick. Inga-Maria IM; Akesson. Per P; Rasmussen. Magnus M; Schmidtchen. Artur A; Björck. Lars L
Key Findings
- SIC protein from S. pyogenes can inactivate human antimicrobial peptides LL‑37 and neutrophil alpha‑defensin.
- Inactivation of these peptides protects the bacteria from being killed by the immune system.
- SIC from the M1 serotype is more effective at this than SIC from less invasive serotypes (M12, M55).
Practical Outcomes
- If you’re considering LL‑37 supplementation, be aware that active Streptococcus pyogenes infections could neutralize its effects. This highlights the importance of managing bacterial infections before relying on LL‑37 for immune support. No direct dosing changes are suggested, but monitoring infection status may be prudent.
Summary
The study shows that a protein called SIC, made by some strains of the bacteria Streptococcus pyogenes, can block two of our body's natural antibiotics – neutrophil alpha‑defensin and LL‑37. This blocking helps the bacteria survive, especially the more dangerous M1 strain, which makes a stronger version of SIC.
Abstract
Some isolates of the significant human pathogen Streptococcus pyogenes, including virulent strains of the M1 serotype, secrete protein SIC. This molecule, secreted in large quantities, interferes with complement function. As a result of natural selection, SIC shows a high degree of variation. Here we provide a plausible explanation for this variation and the fact that strains of the M1 serotype are the most frequent cause of severe invasive S. pyogenes infections. Thus, protein SIC was found to inactivate human neutrophil alpha-defensin and LL-37, two major antibacterial peptides involved in bacterial clearance. This inactivation protected S. pyogenes against the antibacterial effect of the peptides. Moreover, SIC isolated from S. pyogenes of the M1 serotype was more powerful in this respect than SIC variants from strains of M serotypes 12 and 55, serotypes rarely connected with invasive infections.
Study Information
pubmed
2003
2003-03-05T00:00:00.000Z
10.1074/jbc.m301995200