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Streptococcal protein FOG, a novel matrix adhesin interacting with collagen I in vivo
D Patric Nitsche1, Helena M Johansson, Inga-Maria Frick
1Department of Clinical Sciences, Section for Clinical and Experimental Infectious Medicine, Biomedical Center, Lund University, S-22184 Lund, Sweden.
Abstract:
Group G streptococcus (GGS) is a human pathogen of emerging clinical significance. It causes skin and soft tissue infections, occasionally resulting in life-threatening conditions such as sepsis and necrotizing fasciitis. We recently identified FOG, a novel surface protein of GGS with fibrinogen binding and immune evasion properties. Here we investigated the role of FOG in streptococcal primary adhesion to host tissue. A FOG-expressing clinical isolate adhered more efficiently to human skin biopsies ex vivo and to the murine dermis in vivo than a FOG-deficient strain. Scanning and transmission electron microscopy of skin specimens exhibited that this property was assigned to the ability of FOG to interact with collagen I, a major interstitial component of the dermis. Overlay experiments with human skin extracts and radiolabeled FOG followed by matrix-assisted laser desorption/ionization time of flight mass spectrometry analysis identified both the alpha1- and alpha2-chains of collagen I as targets for FOG. Transmission electron microscopy of the molecular complexes revealed thread-like FOG molecules binding via their NH2 termini to distinct sites on collagen I monomers and fibrils. The results demonstrate that FOG is important for GGS adhesion in vivo, implying a pathogenic role for this surface protein.
Insights
Group G streptococcus uses its FOG protein to bind collagen I in host tissues. This interaction enhances bacterial adhesion, contributing to skin infections and potentially severe conditions.
Area of Science:
- Microbiology
- Pathogen-Host Interactions
- Dermatology
Background:
- Group G streptococcus (GGS) is an emerging human pathogen causing significant skin and soft tissue infections.
- A novel surface protein, FOG, was recently identified in GGS, possessing fibrinogen binding and immune evasion capabilities.
- The role of FOG in the initial attachment of GGS to host tissues remained largely unexplored.
Purpose of the Study:
- To investigate the function of the FOG protein in the primary adhesion of Group G streptococcus to host tissues.
- To determine if FOG mediates the interaction between GGS and collagen I, a key component of the dermis.
Main Methods:
- Comparative analysis of adhesion efficiency between FOG-expressing and FOG-deficient GGS strains using ex vivo human skin biopsies and in vivo murine dermis models.
- Scanning and transmission electron microscopy to visualize bacterial-tissue interactions.
- Biochemical assays, including overlay experiments with radiolabeled FOG and human skin extracts, followed by mass spectrometry (MALDI-TOF) to identify FOG's binding targets.
- Transmission electron microscopy to characterize the molecular complexes formed between FOG and collagen I.
Main Results:
- A clinical GGS isolate expressing FOG demonstrated significantly higher adhesion to human skin ex vivo and murine dermis in vivo compared to a FOG-deficient strain.
- Electron microscopy revealed that FOG facilitates GGS adhesion by interacting with collagen I, a major component of the dermal extracellular matrix.
- Mass spectrometry identified both alpha1 and alpha2 chains of collagen I as direct binding targets for the FOG protein.
- Detailed ultrastructural analysis showed FOG molecules binding to collagen I monomers and fibrils via their NH2 termini.
Conclusions:
- The FOG protein plays a crucial role in the in vivo adhesion of Group G streptococcus to host tissues, specifically through its interaction with collagen I.
- This collagen-binding ability of FOG likely contributes to the pathogenesis of GGS infections, particularly skin and soft tissue infections.
- Targeting the FOG-collagen I interaction could represent a novel therapeutic strategy to prevent or treat GGS infections.
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