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The group B streptococcal C5a peptidase is both a specific protease and an invasin
Qi Cheng1, Deborah Stafslien, Sai Sudha Purushothaman
1Department of Microbiology, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Abstract:
The group B streptococcus (GBS) is a major cause of pneumonia, sepsis, and meningitis in neonates and a serious cause of mortality or morbidity in immunocompromised adults. Although these streptococci adhere efficiently and invade a variety of tissue-specific epithelial and endothelial cells, adhesins and invasins are still unknown. All serotypes of GBS studied to date express C5a peptidase (SCPB) on their surface. This investigation addresses the possibility that this relatively large surface protein has additional activities. Rabbit anti-SCPB serum inhibited invasion of lung epithelial A549 cells by the serotype Ia strain O90R, suggesting that SCPB is an invasin. This was confirmed by inserting an in-frame 25-amino-acid deletion into the scpB gene. Invasion of HEp2 and A549 human cell lines was significantly reduced by the mutation. Enzyme-linked immunosorbent assays were used to demonstrate that purified SCPB protein binds directly to HEp2 and A549 cells and also binds the extracellular matrix protein fibronectin. Binding was dose dependent and saturable. These results suggested that SCPB is one of several potential invasins essential for GBS colonization of damaged epithelium.
Insights
Group B Streptococcus (GBS) surface protein C5a peptidase (SCPB) acts as an invasin, facilitating bacterial entry into host cells. This finding reveals SCPB
Area of Science:
- Microbiology
- Cell Biology
- Infectious Diseases
Background:
- Group B Streptococcus (GBS) causes severe neonatal infections and affects immunocompromised adults.
- GBS adheres to and invades epithelial and endothelial cells, but its adhesins and invasins remain largely unidentified.
- All GBS serotypes express surface C5a peptidase (SCPB).
Purpose of the Study:
- To investigate potential additional functions of the GBS surface protein SCPB.
- To determine if SCPB possesses invasin activity.
Main Methods:
- Utilized rabbit anti-SCPB serum to assess GBS invasion inhibition.
- Generated a GBS mutant with a 25-amino-acid deletion in the scpB gene.
- Employed enzyme-linked immunosorbent assays (ELISAs) to evaluate direct binding of purified SCPB to human cell lines and fibronectin.
Main Results:
- Anti-SCPB serum inhibited GBS invasion of A549 lung epithelial cells.
- The scpB deletion mutant showed significantly reduced invasion of HEp2 and A549 cells.
- Purified SCPB directly bound to HEp2 and A549 cells and fibronectin in a dose-dependent and saturable manner.
Conclusions:
- SCPB functions as an invasin for GBS.
- SCPB mediates bacterial entry into host cells by binding to epithelial cells and extracellular matrix proteins like fibronectin.
- SCPB is identified as a potential key factor in GBS colonization of damaged epithelial tissues.