The rgg Gene of Streptococcus pyogenes NZ131 Positively Influences Extracellular SPE B Production

ABSTRACT Streptococcus pyogenes produces several extracellular proteins, including streptococcal erythrogenic toxin B (SPE B), also known as streptococcal pyrogenic exotoxin B and streptococcal proteinase. Several reports suggest that SPE B contributes to the virulence associated with S. pyogenes; however, little is known about its regulation. Nucleotide sequence data revealed the presence, upstream of the speB gene, of a gene, designatedrgg, that was predicted to encode a polypeptide similar to previously described positive regulatory factors. The putative Rgg polypeptide of S. pyogenes NZ131 consisted of 280 amino acids and had a predicted molecular weight of 33,246. To assess the potential role of Rgg in the production of SPE B, the rgggene was insertionally inactivated in S. pyogenes NZ131, which resulted in markedly decreased SPE B production, as determined both by immunoblotting and caseinolytic activity on agar plates. However, the production of other extracellular products, including streptolysin O, streptokinase, and DNase, was not affected. Complementation of the rgg mutant with an intactrgg gene copy in S. pyogenes NZ131 could restore SPE B production and confirmed that the rgg gene product is involved in the production of SPE B.

Streptococcal cysteine proteinase releases kinins: a virulence mechanism.

Previous work has indicated a crucial role for the extracellular cysteine proteinase of Streptococcus pyogenes in the pathogenicity and virulence of this important human pathogen. Here we find that the purified streptococcal cysteine proteinase releases biologically active kinins from their purified precursor protein, H-kininogen, in vitro, and from kininogens present in the human plasma, ex vivo. Kinin liberation in the plasma is due to the direct action of the streptococcal proteinase on the kininogens, and does not involve the previous activation of plasma prekallikrein, the physiological plasma kininogenase. Judged from the amount of released plasma kinins the bacterial proteinase is highly efficient in its action. This is also the case in vivo. Injection of the purified cysteine proteinase into the peritoneal cavity of mice resulted in a progressive cleavage of plasma kininogens and the concomitant release of kinins over a period of 5 h. No kininogen degradation was seen in mice when the cysteine proteinase was inactivated by the specific inhibitor, Z-Leu-Val-Gly-CHN2, before administration. Intraperitoneal administration into mice of living S. pyogenes bacteria producing the cysteine proteinase induced a rapid breakdown of endogenous plasma kininogens and release of kinins. Kinins are hypotensive, they increase vascular permeability, contract smooth muscle, and induce fever and pain. The release of kinins by the cysteine proteinase of S. pyogenes could therefore represent an important and previously unknown virulence mechanism in S. pyogenes infections.

Identification of an extracellular plasmin binding protein from nephritogenic streptococci.

Examination of the extracellular products of nephritis(+) and nephritis(-) group A streptococci revealed the presence of a 46-kD protein secreted by nephritogenic strains that binds to human plasmin. Immunological data revealed that this protein, called nephritis plasmin binding protein (NPBP), is not related to group A streptokinase nor to a recently described streptococcal dehydrogenase protein. The binding of human plasmin to this protein can be blocked by epsilon-amino caproic acid, indicating the importance of lysine groups in the binding process. Mutanolysin extracts of cell walls from these nephritogenic strains probed with anti-NPBP antibody were negative for cell wall-bound NPBP. Serological data with acute poststreptococcal glomerulonephritis (APSGN) and acute rheumatic fever sera indicated that the protein reacts preferentially with APSGN sera. Amino acid sequence analysis and immunological reactivity suggest NPBP is the streptococcal pyrogenic exotoxin B precursor, also previously described as zymogen (streptococcal proteinase precursor). The secretion of both group A streptokinase and a secreted plasmin binding protein in the same nephritogenic strain raises an intriguing hypothesis of the mechanisms of action of this protein in APSGN.