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Sequencing of genes within the vir regulon of Streptococcus pyogenes type M15--an opacity factor-positive serotype
V Katerov1, C Schalén, A A Totolian
1Institute of Experimental Medicine, Academy of the Medical Sciences, St. Petersburg, Russia.
Abstract:
Major virulence determinants of group A streptococci, such as M-protein, immunoglobulin Fc-receptors (FcRA, EmmL) and C5a peptidase, appear to be genetically co-regulated, their genes being located within a vir regulon. We studied the organization of these genes in a group A, type M15 strain of Streptococcus pyogenes, previously defined as OF-, by hybridization analysis of chromosomal DNA and of an S. pyogenes gene library in Escherichia coli, and by gene sequencing. Within the vir regulon, in addition to the virR and scpA genes, three so-called emm-related genes were found: fcrA, emmL and enn. Whereas IgG Fc-binding proteins were encoded by fcrA and emmL, the product of enn was not identified. The presence of three emm-related genes in this region is reminescent of vir regulon organization in OF+ rather than OF- strains as earlier defined by others. Furthermore, analysis of the deduced product of the emmL gene showed deletions and amino acid substitutions within the PGTS-rich domain and membrane anchor, which thus resembles corresponding products of OF+ rather than OF- strains. In view of these findings, the opacity factor (OF) activity of the strain was tested using growth supernatant, with negative outcome. However, a concentrated SDS cell extract revealed definite OF activity. One of two other type M15 reference strains also showed definite OF activity in SDS extracts. We therefore propose that type M15 strains belong to the OF+ category but often show low levels of expression of OF.
Insights
Group A Streptococcus virulence genes, including M-protein and Fc receptors, are co-regulated. Type M15 strains, previously considered OF-, exhibit opacity factor (OF) activity in cell extracts, suggesting OF+ classification.
Area of Science:
- Microbiology
- Molecular Biology
- Bacteriology
Background:
- Group A Streptococcus (GAS) virulence factors like M-protein, Fc receptors (FcRA, EmmL), and C5a peptidase are often co-regulated within a vir regulon.
- Understanding the genetic organization of these virulence factors is crucial for deciphering GAS pathogenesis.
Purpose of the Study:
- To investigate the gene organization of the vir regulon in a type M15 Streptococcus pyogenes strain previously characterized as opacity factor-negative (OF-).
- To re-evaluate the opacity factor (OF) status of type M15 strains based on molecular and functional analyses.
Main Methods:
- Hybridization analysis of chromosomal DNA and an S. pyogenes gene library in E. coli.
- Gene sequencing of the vir regulon.
- Opacity factor (OF) activity assays using growth supernatant and SDS cell extracts.
Main Results:
- The vir regulon in the studied type M15 strain contained three emm-related genes (fcrA, emmL, enn) and the scpA gene.
- The EmmL protein showed structural similarities to products from OF+ strains, not OF- strains.
- While OF activity was absent in supernatant, it was detected in SDS cell extracts of the strain and other type M15 reference strains.
Conclusions:
- Type M15 Streptococcus pyogenes strains should be classified as OF+.
- The observed OF activity in type M15 strains may be due to low-level expression, often undetectable in standard assays.
- The genetic organization of the vir regulon in type M15 strains resembles that of OF+ strains.