title: 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.
authors.affiliation: Department of Molecular Sciences, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA.
authors.forename: Mohammed M
authors.initials: MM
authors.lastname: Nooh
authors.forename: Ramy K
authors.initials: RK
authors.lastname: Aziz
authors.forename: Malak
authors.initials: M
authors.lastname: Kotb
authors.forename: Alexey
authors.initials: A
authors.lastname: Eroshkin
authors.forename: Woei-Jer
authors.initials: WJ
authors.lastname: Chuang
authors.forename: Thomas
authors.initials: T
authors.lastname: Proft
authors.forename: Rita
authors.initials: R
authors.lastname: Kansal
mesh_terms: D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000737:chemistry / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D001427:Bacterial Toxins / Q000737:chemistry / Q000378:metabolism*; D019295:Computational Biology; D005098:Exotoxins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D013297:Streptococcus pyogenes / Q000201:enzymology / Q000378:metabolism*; D013379:Substrate Specificity; D018089:Superantigens / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D005098:Exotoxins; D018089:Superantigens; C027951:erythrogenic toxin; C107894:mitogenic exotoxin Z protein, Streptococcus