Naturally Occurring Rgg Variant in Serotype M3 Streptococcus pyogenes Does Not Activate speB Expression Due to Altered Specificity of DNA Binding

• Published in: Infection and Immunity 2009-12, Vol.77 (12), p.5411-5417
• Main Authors: Kappeler, Kyle V, Anbalagan, Srivishnupriya, Dmitriev, Alexander V, McDowell, Emily J, Neely, Melody N, Chaussee, Michael S
• Format: Article
• Language: English
• Subjects: Amino Acid Substitution - genetics; Antigens, Bacterial - analysis; Bacterial Outer Membrane Proteins - analysis; Bacterial Proteins - biosynthesis; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Carrier Proteins - analysis; DNA, Bacterial - metabolism; Electrophoretic Mobility Shift Assay; Exotoxins - biosynthesis; Gene Expression Regulation, Bacterial; Molecular Pathogenesis; Mutation, Missense; Promoter Regions, Genetic; Protein Binding; Serotyping; Streptococcus pyogenes; Streptococcus pyogenes - genetics; Streptococcus pyogenes - physiology; Trans-Activators - genetics; Trans-Activators - metabolism
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.00373-09

The transcriptional regulator Rgg of Streptococcus pyogenes is essential for expression of the secreted cysteine protease SpeB. Although all isolates of S. pyogenes possess the speB gene, not all of them produce the protein in vitro. In a murine model of infection, the absence of SpeB production is associated with invasive disease. We speculated that naturally occurring mutations in rgg, which would also abrogate SpeB production, may be present in invasive isolates of S. pyogenes. Examination of the inferred Rgg sequences available in public databases revealed that the rgg gene in strain MGAS315 (a serotype M3 strain associated with invasive disease) encodes a proline at amino acid position 103 (Rgg₁₀₃P); in contrast, all other strains encode a serine at this position (Rgg₁₀₃S). A caseinolytic assay and Western blotting indicated that strain MGAS315 does not produce SpeB in vitro. Gene-swapping experiments showed that the rgg gene of MGAS315 is solely responsible for the lack of SpeB expression. In contrast to Rgg₁₀₃S, Rgg₁₀₃P does not bind to the speB promoter in gel shift assays, which correlates with a lack of speB expression. Despite its inability to activate speB expression, Rgg₁₀₃P retains the ability to bind to DNA upstream of norA and to influence its expression. Overall, this study illustrates how variation at the rgg locus may contribute to the phenotypic diversity of S. pyogenes.