Related Experiment Videos
Streptococcus pyogenes type IIa IgG Fc receptor expression is co-ordinately regulated with M protein and
D La Penta1, X P Zhang, P P Cleary
1Department of Microbiology, University of Minnesota, Minneapolis 55455.
Abstract:
Streptococcus pyogenes is an important agent of human disease which expresses a variety of proteins and polysaccharides on its surface. Surface molecules M protein and streptococcal C5a peptidase (SCPA) are virulence factors which undergo concurrent phase variation and are under the co-ordinate control of the virR locus. Most opacity factor-positive (OF+) strains of S. pyogenes also express IgG Fc receptor proteins on their surface. These studies were initiated to determine whether the type IIa Fc receptor on the surface of S. pyogenes phase-varies with members of this regulatory circuit. Several methods were applied to M+ and M- variant strains to evaluate this question. (i) Immunoblot assays quantified Fc receptors on whole cells by using human IgG myeloma protein and receptor-specific antibody. M+ strains bound IgG and antibody specific for Fc protein, whereas M- strains did not. (ii) Enzyme-linked immunosorbent assays quantified Fc receptor antigen expression and showed that M+ strains produce more Fc receptor protein than their M- derivatives. (iii) Quantitative RNA dot blots showed that the message for the Fc receptor gene (fcrA) was reduced in M- strains. RNA from M+ strains hybridized to the fcrA probe at a greater dilution than that from their M- counterparts. (iv) Northern hybridization showed that the fcrA transcript is 1200 nucleotides in size and distinct from transcripts for M and SCPA proteins. These data are evidence for the co-ordinate transcriptional control of the Fc receptor, M protein, and SCPA and show that these proteins co-ordinately phase-vary within the same regulatory circuit.
Insights
Streptococcus pyogenes virulence factors, including M protein, streptococcal C5a peptidase (SCPA), and Fc receptors, are coordinately controlled. These surface proteins phase-vary together, indicating a shared regulatory circuit in pathogenic bacteria.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Streptococcus pyogenes possesses surface proteins like M protein and streptococcal C5a peptidase (SCPA) that are crucial virulence factors.
- These virulence factors, M protein and SCPA, are known to undergo phase variation under the control of the virR locus.
- Opacity factor-positive (OF+) S. pyogenes strains typically express IgG Fc receptor proteins on their surface.
Purpose of the Study:
- To investigate if the type IIa Fc receptor on S. pyogenes surface exhibits co-ordinate phase variation with M protein and SCPA.
- To elucidate the regulatory mechanisms governing the expression of S. pyogenes surface proteins.
Main Methods:
- Immunoblot assays were used to quantify Fc receptors on whole bacterial cells.
- Enzyme-linked immunosorbent assays (ELISAs) assessed Fc receptor antigen expression levels.
- Quantitative RNA dot blots and Northern hybridization analyzed the expression of the Fc receptor gene (fcrA) at the transcript level.
Main Results:
- M+ S. pyogenes strains demonstrated significant binding of IgG and Fc receptor-specific antibodies, unlike M- strains.
- ELISAs confirmed higher Fc receptor protein expression in M+ strains compared to their M- counterparts.
- RNA analysis revealed reduced fcrA gene message in M- strains, indicating transcriptional regulation.
Conclusions:
- The study provides evidence for the co-ordinate transcriptional control of Fc receptor, M protein, and SCPA in Streptococcus pyogenes.
- These surface proteins (Fc receptor, M protein, SCPA) phase-vary together, suggesting they are part of the same regulatory circuit.
- The findings contribute to understanding the coordinated regulation of virulence factors in pathogenic bacteria.