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Updated: Aug 14, 2026
Invasion of Human Cells by a Bacterial Pathogen
Published on: March 21, 2011
SpeB modulates fibronectin-dependent internalization of Streptococcus pyogenes by efficient proteolysis of
Patrik Nyberg1, Magnus Rasmussen1, Ulrich von Pawel-Rammingen1
1Department of Cell and Molecular Biology, Section for Molecular Pathogenesis, Lund University, BMC, B14, Tornavägen 10, S-22184 Lund, Sweden.
Abstract:
SpeB is a cysteine proteinase and virulence determinant secreted by the important human pathogen Streptococcus pyogenes. Recent investigations have suggested a role for SpeB in streptococcal entry into human cells. However, conflicting data concerning the contribution of SpeB to internalization have been presented. Protein F1 is a cell-wall-attached fibronectin (Fn)-binding protein that is present in a majority of streptococcal isolates and is important for internalization. This study shows that protein F1 is efficiently degraded by SpeB, and that removal of protein F1 from the bacterial surface leads to reduced internalization. Whereas M1 protein and protein H, two additional surface proteins of S. pyogenes that bind human plasma proteins, are protected from proteolytic degradation by their ligands, protein F1 is readily cleaved by SpeB also when in complex with Fn. This finding, and the connection between the presence of Fn at the bacterial surface and entry into human cells, suggest that SpeB plays a role in the regulation of the internalization process.
Insights
Streptococcus pyogenes SpeB proteinase degrades cell-wall protein F1, reducing bacterial entry into human cells. This suggests SpeB regulates streptococcal internalization by cleaving fibronectin-binding protein F1.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Streptococcus pyogenes is a significant human pathogen.
- SpeB (Streptococcal pyrogenic exotoxin B) is a secreted cysteine proteinase and virulence factor.
- The role of SpeB in streptococcal internalization into human cells remains debated.
Purpose of the Study:
- To investigate the role of SpeB in the internalization of Streptococcus pyogenes into human cells.
- To determine if SpeB degrades surface proteins involved in bacterial entry.
- To elucidate the mechanism by which SpeB influences streptococcal internalization.
Main Methods:
- Degradation assays of bacterial surface proteins by SpeB.
- Analysis of bacterial internalization following protein F1 removal.
- Investigation of SpeB's effect on protein F1 in the presence of fibronectin (Fn).
Main Results:
- SpeB efficiently degrades protein F1, a fibronectin-binding protein crucial for internalization.
- Removal of protein F1 from the bacterial surface significantly reduces streptococcal internalization.
- Unlike other surface proteins (M1, protein H), protein F1 is degraded by SpeB even when bound to fibronectin.
- Fibronectin presence on the bacterial surface correlates with streptococcal entry into human cells.
Conclusions:
- SpeB plays a regulatory role in Streptococcus pyogenes internalization.
- SpeB-mediated degradation of protein F1 is a key mechanism influencing bacterial entry.
- The interaction of SpeB with fibronectin-bound protein F1 is critical for regulating streptococcal internalization into host cells.
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