Two novel superantigens found in both group A and group C Streptococcus.
Two novel streptococcal superantigen genes (speL(Se) and speM(Se)) were identified from the Streptococcus equi genome database at the Sanger Center. Genotyping of 8 S. equi isolates and 40 Streptococcus pyogenes isolates resulted in the detection of the orthologous genes speL and speM in a restricted number of S. pyogenes isolates (15 and 5%, respectively). Surprisingly, the novel superantigen genes could not be found in any of the analyzed S. equi isolates. The results suggest that both genes are located on a mobile element that enables gene transfer between individual isolates and between streptococci from different Lancefield groups. S. equi pyrogenic exotoxin L (SPE-L(Se))/streptococcal pyrogenic exotoxin L (SPE-L) and SPE-M(Se)/SPE-M are most closely related to SMEZ, SPE-C, SPE-G, and SPE-J, but build a separate branch within this group. Recombinant SPE-L (rSPE-L) and rSPE-M were highly mitogenic for human peripheral blood lymphocytes, with half-maximum responses at 1 and 10 pg/ml, respectively. The results from competitive binding experiments suggest that both proteins bind major histocompatibility complex class II at the beta-chain, but not at the alpha-chain. The most common targets for both toxins were human Vbeta1.1 expressing T cells. Seroconversion against SPE-L and SPE-M was observed in healthy blood donors, suggesting that the toxins are expressed in vivo. Interestingly, the speL gene is highly associated with S. pyogenes M89, a serotype that is linked to acute rheumatic fever in New Zealand.
Proft
Thomas
T
Department of Molecular Medicine and Pathology, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand.
Webb
Phillip D
PD
Handley
Vanessa
V
Fraser
John D
JD
D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D003001:Cloning, Molecular; D005098:Exotoxins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005838:Genotype; D000949:Histocompatibility Antigens Class II / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000276:immunology; D013291:Streptococcus / Q000276:immunology*; D013297:Streptococcus pyogenes / Q000276:immunology*; D018089:Superantigens / Q000235:genetics*
D001426:Bacterial Proteins; D005098:Exotoxins; D000949:Histocompatibility Antigens Class II; D008565:Membrane Proteins; D016693:Receptors, Antigen, T-Cell, alpha-beta; C117980:SpeA protein, Streptococcus pyogenes; D018089:Superantigens; C027951:erythrogenic toxin