Streptococcal Mitogenic Exotoxin, SmeZ, Is the Most Susceptible M1T1 Streptococcal Superantigen to Degradation by the Streptococcal Cysteine Protease, SpeB

Abstract

Superantigens (SAgs) play an important role in the pathogenesis of severe invasive infections caused by Group A Streptococcus (GAS). We had shown earlier that the expression of streptococcal cysteine protease SpeB results in partial loss of the immune-stimulating activity of the native secreted GAS SAgs, namely the streptococcal pyrogenic exotoxins produced by the globally disseminated M1T1 GAS strain, associated with invasive infections worldwide. In this study, we examined the susceptibility of each of the M1T1 recombinant SAgs to degradation by rSpeB. Whereas SmeZ was degraded completely within 30 min of incubation with rSpeB, SpeG, and SpeA were more resistant and SpeJ was completely unaffected by the proteolytic effects of this protease. Proteomic analyses demonstrated that the order of susceptibility of the M1T1 SAgs to SpeB proteolysis is unaltered when they are present in a mixture that reflects their native physiological status. As expected, the degradation of SmeZ abolished its immune stimulatory activity. In silico sequence disorder and structural analyses revealed that SmeZ, unlike the three other structurally related SAgs, possesses a putative SpeB cleavage site within an area of the protein likely to be exposed to the surface. The study provides evidence for the effect of subtle structural differences between highly similar SAgs on their biological activity.

CovS Simultaneously Activates and Inhibits the CovR-Mediated Repression of Distinct Subsets of Group A Streptococcus Virulence Factor-Encoding Genes

“…The cysteine protease SpeB was the only protein detected by these antibodies using secreted proteins from wild-type strain MGAS2221. In part, this pattern of reactivity may be due to the SpeB-mediated degradation of SLO, SPN, and Mac (note that SpeB also has low-level activity against SpeA) (25,32). The covS mutant strain 2221covS⌬1bp secreted all of the proteins assayed other than SpeB, a secretion pattern identical to that of the well-described clinical covS mutant isolate MGAS5005 (32).…”

Identification of Three Novel Superantigen-Encoding Genes in Streptococcus equi subsp. zooepidemicus , szeF , szeN , and szeP

“…For example, the culture supernatants of only 4 of 45 isolates from cases of uterine infection or abortion examined in this study possessed mitogenic activity (P Ͻ 0.00093). However, we note that superantigen activity in some strains could be masked by the production of cytolysins or other factors that interfere with their activity (31,48). It is interesting that the majority of truncated szeF sequences (18/20) clustered together in szeF group C and that the remaining two group C szeF sequences contained an A-to-G substitution at bp 457 leading to a K-to-E substitution at amino acid 153.…”

“…zooepidemicus sAgs are highlighted in blue and red, respectively. The five main groups of sAgs are indicated (30,31). The unrooted tree was based on the alignment of amino acid sequences using ClustalW (47) and constructed using MEGA 4 (45).…”

Individual Genetic Variations Directly Effect Polarization of Cytokine Responses to Superantigens Associated with Streptococcal Sepsis: Implications for Customized Patient Care

“…We isolated PBMCs from various subjects, as previously described (40). APC-depleted T cells were purified by subjecting freshly isolated PBMCs to one cycle of erythrocyte rosetting; they were then isolated with the human pan T cell isolation kit and autoMACS, according to the manufacturer's instructions (Miltenyi Biotec).…”