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Quantitative differences in specific binding of fibrinogen fragment D by M-positive and M-negative group-A
Abstract:
Selected M-positive and M-negative group-A streptococcal strains were investigated with respect to their selective absorption of plasmin fibrinogen degradation products (FDP) in a simple batch technique. After incubation of killed streptococci with the FDP mixture, the centrifuged supernatants were investigated by SDS-electrophoresis and the binding capacity of the strains was calculated by evaluation of the scanning curves of stained gels. It was found that there is a specific uptake of the C-terminal fragment D by both M-positive and M-negative strains. Although the M-positive strains bound more fragment D (30%-80%) than did the M-negative strains (10%-15%), it could be clearly shown that the loss of M-protein was not necessarily linked with a total disappearance of fibrinogen binding activity. Fragment D blocked the agglutination of streptococci by fibrinogen. Washing the streptococci preincubated with FDP with a 0.1 M citric acid, 6 M urea buffer, pH 3.0, restored agglutination. Treatment of FDP-incubated bacteria with this buffer was found to be a means of recovering pure fragment D from streptococcal cells. It is suggested that M-positive and M-negative streptococci have qualitatively similar binding sites. These receptors might be reduced in the M-negative streptococci. Human serum albumin and Tween 20 did not influence the interaction between streptococcus and fibrinogen.
Insights
Group A streptococci bind fibrinogen degradation products (FDP), specifically fragment D. While M-positive strains show higher binding, M-negative strains retain some fibrinogen binding activity, suggesting similar but reduced binding sites.
Area of Science:
- Microbiology
- Biochemistry
Background:
- Group A Streptococcus (GAS) is a significant human pathogen.
- M-protein is a key virulence factor in GAS, but its role in fibrinogen interactions is not fully understood.
- Fibrinogen degradation products (FDP) are involved in the host's immune response and can interact with bacterial surface components.
Purpose of the Study:
- To investigate the selective absorption of plasmin fibrinogen degradation products (FDP) by M-positive and M-negative group A streptococcal strains.
- To determine if M-protein influences the binding of FDP, particularly fragment D.
- To explore the nature of streptococcal binding sites for FDP.
Main Methods:
- Utilized a batch technique to incubate killed streptococci with FDP mixtures.
- Analyzed FDP binding using SDS-electrophoresis and scanning densitometry of stained gels.
- Investigated the effect of fragment D on streptococcal agglutination by fibrinogen and the recovery of bound fragment D.
Main Results:
- Both M-positive and M-negative GAS strains specifically absorbed fragment D from FDP.
- M-positive strains exhibited significantly higher fragment D binding (30%-80%) compared to M-negative strains (10%-15%).
- Loss of M-protein did not abolish fibrinogen binding activity, and fragment D inhibited streptococcal agglutination by fibrinogen.
Conclusions:
- Group A streptococci, regardless of M-protein presence, possess qualitatively similar binding sites for fragment D.
- M-protein contributes to, but is not solely responsible for, fibrinogen binding activity.
- Fragment D binding sites may be reduced in M-negative strains, and these sites can be utilized for fragment D recovery.