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Identification and characterization of novel superantigens from Streptococcus pyogenes.

Proft T, Moffatt SL, Berkahn CJ, Fraser JD - J. Exp. Med. (1999)

Bottom Line: All toxins, except rSPE-G, were active on murine T cells, but with reduced potency.The most common targets for the novel SAgs were human Vbeta2.1- and Vbeta4-expressing T cells.This might reflect a specific role for this subset of Vbetas in the immune defense of gram-positive bacteria.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Medicine, School of Medicine, University of Auckland, 92019 Auckland, New Zealand.

ABSTRACT
Three novel streptococcal superantigen genes (spe-g, spe-h, and spe-j) were identified from the Streptococcus pyogenes M1 genomic database at the University of Oklahoma. A fourth novel gene (smez-2) was isolated from the S. pyogenes strain 2035, based on sequence homology to the streptococcal mitogenic exotoxin z (smez) gene. SMEZ-2, SPE-G, and SPE-J are most closely related to SMEZ and streptococcal pyrogenic exotoxin (SPE)-C, whereas SPE-H is most similar to the staphylococcal toxins than to any other streptococcal toxin. Recombinant (r)SMEZ, rSMEZ-2, rSPE-G, and rSPE-H were mitogenic for human peripheral blood lymphocytes with half-maximal responses between 0.02 and 50 pg/ml (rSMEZ-2 and rSPE-H, respectively). SMEZ-2 is the most potent superantigen (SAg) discovered thus far. All toxins, except rSPE-G, were active on murine T cells, but with reduced potency. Binding to a human B-lymphoblastoid line was shown to be zinc dependent with high binding affinity of 15-65 nM. Evidence from modeled protein structures and competitive binding experiments suggest that high affinity binding of each toxin is to the major histocompatibility complex class II beta chain. Competition for binding between toxins was varied and revealed overlapping but discrete binding to subsets of class II molecules in the hierarchical order (SMEZ, SPE-C) > SMEZ-2 > SPE-H > SPE-G. The most common targets for the novel SAgs were human Vbeta2.1- and Vbeta4-expressing T cells. This might reflect a specific role for this subset of Vbetas in the immune defense of gram-positive bacteria.

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Computer generated models of protein structures. The models were  created on a Silicon Graphic computer using InsightII/Homology software. SEA,  SEB, and SPE-C were used as reference proteins to determine structurally conserved regions. The loop regions were generated by random choice. MolScript  software (39) was used for displaying the computer generated images. (a) All  models show a potential zinc binding site within the β-grasp motif of the toxin  structure. Two zinc binding residues are provided by a primary zinc motif (H-X-D) and the third ligand (H or D) comes from either the β9 or β10 strand. The  amino acid residues of the β1-β2 loop that corresponds to the HLA-DRI α  chain binding site in SEA and SEB are shown on the right side of the models. In  all three protein models, this loop region is less hydrophobic than in SEA and  SEB, suggesting the lack of the α chain binding site. A, Crystal structures of SPE-C  (25); B, SMEZ-2; C, SPE-G; D, SPE-H. (b) SMEZ-2 model, showing the predicted location of the 17 residues that are different between SMEZ and SMEZ-2.  The first residue is from SMEZ-2, followed by the position on the primary protein sequence and the corresponding residue on SMEZ.
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Figure 6: Computer generated models of protein structures. The models were created on a Silicon Graphic computer using InsightII/Homology software. SEA, SEB, and SPE-C were used as reference proteins to determine structurally conserved regions. The loop regions were generated by random choice. MolScript software (39) was used for displaying the computer generated images. (a) All models show a potential zinc binding site within the β-grasp motif of the toxin structure. Two zinc binding residues are provided by a primary zinc motif (H-X-D) and the third ligand (H or D) comes from either the β9 or β10 strand. The amino acid residues of the β1-β2 loop that corresponds to the HLA-DRI α chain binding site in SEA and SEB are shown on the right side of the models. In all three protein models, this loop region is less hydrophobic than in SEA and SEB, suggesting the lack of the α chain binding site. A, Crystal structures of SPE-C (25); B, SMEZ-2; C, SPE-G; D, SPE-H. (b) SMEZ-2 model, showing the predicted location of the 17 residues that are different between SMEZ and SMEZ-2. The first residue is from SMEZ-2, followed by the position on the primary protein sequence and the corresponding residue on SMEZ.

Mentions: To determine if there were significant structural differences, the protein structures of SMEZ-2, SPE-G, and SPE-H were modelled onto the superimposed structurally conserved regions of SEA, SEB, and SPE-C (Fig. 6). The models showed that in all three proteins, the two amino acid side chains of the COOH-terminal primary zinc binding motif are in close proximity to a third potential zinc ligand to build a zinc binding site, similar to the zinc binding site observed in SEA and SPE-C.


Identification and characterization of novel superantigens from Streptococcus pyogenes.

Proft T, Moffatt SL, Berkahn CJ, Fraser JD - J. Exp. Med. (1999)

Computer generated models of protein structures. The models were  created on a Silicon Graphic computer using InsightII/Homology software. SEA,  SEB, and SPE-C were used as reference proteins to determine structurally conserved regions. The loop regions were generated by random choice. MolScript  software (39) was used for displaying the computer generated images. (a) All  models show a potential zinc binding site within the β-grasp motif of the toxin  structure. Two zinc binding residues are provided by a primary zinc motif (H-X-D) and the third ligand (H or D) comes from either the β9 or β10 strand. The  amino acid residues of the β1-β2 loop that corresponds to the HLA-DRI α  chain binding site in SEA and SEB are shown on the right side of the models. In  all three protein models, this loop region is less hydrophobic than in SEA and  SEB, suggesting the lack of the α chain binding site. A, Crystal structures of SPE-C  (25); B, SMEZ-2; C, SPE-G; D, SPE-H. (b) SMEZ-2 model, showing the predicted location of the 17 residues that are different between SMEZ and SMEZ-2.  The first residue is from SMEZ-2, followed by the position on the primary protein sequence and the corresponding residue on SMEZ.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC1887688&req=5

Figure 6: Computer generated models of protein structures. The models were created on a Silicon Graphic computer using InsightII/Homology software. SEA, SEB, and SPE-C were used as reference proteins to determine structurally conserved regions. The loop regions were generated by random choice. MolScript software (39) was used for displaying the computer generated images. (a) All models show a potential zinc binding site within the β-grasp motif of the toxin structure. Two zinc binding residues are provided by a primary zinc motif (H-X-D) and the third ligand (H or D) comes from either the β9 or β10 strand. The amino acid residues of the β1-β2 loop that corresponds to the HLA-DRI α chain binding site in SEA and SEB are shown on the right side of the models. In all three protein models, this loop region is less hydrophobic than in SEA and SEB, suggesting the lack of the α chain binding site. A, Crystal structures of SPE-C (25); B, SMEZ-2; C, SPE-G; D, SPE-H. (b) SMEZ-2 model, showing the predicted location of the 17 residues that are different between SMEZ and SMEZ-2. The first residue is from SMEZ-2, followed by the position on the primary protein sequence and the corresponding residue on SMEZ.
Mentions: To determine if there were significant structural differences, the protein structures of SMEZ-2, SPE-G, and SPE-H were modelled onto the superimposed structurally conserved regions of SEA, SEB, and SPE-C (Fig. 6). The models showed that in all three proteins, the two amino acid side chains of the COOH-terminal primary zinc binding motif are in close proximity to a third potential zinc ligand to build a zinc binding site, similar to the zinc binding site observed in SEA and SPE-C.

Bottom Line: All toxins, except rSPE-G, were active on murine T cells, but with reduced potency.The most common targets for the novel SAgs were human Vbeta2.1- and Vbeta4-expressing T cells.This might reflect a specific role for this subset of Vbetas in the immune defense of gram-positive bacteria.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Medicine, School of Medicine, University of Auckland, 92019 Auckland, New Zealand.

ABSTRACT
Three novel streptococcal superantigen genes (spe-g, spe-h, and spe-j) were identified from the Streptococcus pyogenes M1 genomic database at the University of Oklahoma. A fourth novel gene (smez-2) was isolated from the S. pyogenes strain 2035, based on sequence homology to the streptococcal mitogenic exotoxin z (smez) gene. SMEZ-2, SPE-G, and SPE-J are most closely related to SMEZ and streptococcal pyrogenic exotoxin (SPE)-C, whereas SPE-H is most similar to the staphylococcal toxins than to any other streptococcal toxin. Recombinant (r)SMEZ, rSMEZ-2, rSPE-G, and rSPE-H were mitogenic for human peripheral blood lymphocytes with half-maximal responses between 0.02 and 50 pg/ml (rSMEZ-2 and rSPE-H, respectively). SMEZ-2 is the most potent superantigen (SAg) discovered thus far. All toxins, except rSPE-G, were active on murine T cells, but with reduced potency. Binding to a human B-lymphoblastoid line was shown to be zinc dependent with high binding affinity of 15-65 nM. Evidence from modeled protein structures and competitive binding experiments suggest that high affinity binding of each toxin is to the major histocompatibility complex class II beta chain. Competition for binding between toxins was varied and revealed overlapping but discrete binding to subsets of class II molecules in the hierarchical order (SMEZ, SPE-C) > SMEZ-2 > SPE-H > SPE-G. The most common targets for the novel SAgs were human Vbeta2.1- and Vbeta4-expressing T cells. This might reflect a specific role for this subset of Vbetas in the immune defense of gram-positive bacteria.

Show MeSH
Related in: MedlinePlus