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Streptokinase variants from Streptococcus pyogenes isolates display altered plasminogen activation characteristics -
Simon M Cook1, Amanda Skora, Christine M Gillen
1Illawarra Health and Medical Research Institute, School of Biological Sciences, University of Wollongong, Wollongong, Australia.
Streptococcus pyogenes streptokinase variants exhibit distinct plasminogen activation pathways. Type-2b variants show reduced virulence, impacting the pathogenesis of group A Streptococcus infections.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Streptococcus pyogenes (group A Streptococcus, GAS) produces streptokinase (SK), a key virulence factor.
- SK gene sequences (ska) exhibit polymorphism, classified into type-1, type-2a, and type-2b variants.
- Understanding SK variant function is crucial for deciphering GAS pathogenesis.
Purpose of the Study:
- To investigate the functional differences between GAS streptokinase variants.
- To determine the impact of distinct SK variants on plasminogen activation and GAS virulence.
Main Methods:
- Far-UV circular dichroism spectroscopy to assess secondary structure.
- Biochemical assays to evaluate plasminogen activation and binding affinity.
- Genetic exchange of ska variants in a GAS M1T1 strain (5448) followed by mouse models of invasive disease.
Main Results:
- All SK variants displayed similar secondary structures.
- Type-2b SK variants showed impaired non-proteolytic activation of Glu-plasminogen and significantly reduced binding affinity.
- Type-2b and type-1 SK-plasmin complexes were susceptible to α(2)-antiplasmin inhibition.
- Exchanging ska(type-2a) with ska(type-2b) reduced GAS virulence, while exchange with ska(type-1) increased virulence in a mouse model.
Conclusions:
- GAS streptokinase variants possess distinct mechanisms for plasminogen activation.
- These functional differences directly influence the virulence and pathogenesis of Streptococcus pyogenes.
- SK variant type is a significant determinant of GAS disease severity.
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