Structural basis for the neutralization and specificity of Staphylococcal enterotoxin B against its MHC Class II binding site

Abstract

Staphylococcal enterotoxin (SE) B is among the potent toxins produced by Staphylococcus aureus that cause toxic shock syndrome (TSS), which can result in multi-organ failure and death. Currently, neutralizing antibodies have been shown to be effective immunotherapeutic agents against this toxin, but the structural basis of the neutralizing mechanism is still unknown. In this study, we generated a neutralizing monoclonal antibody, 3E2, against SEB, and analyzed the crystal structure of the SEB-3E2 Fab complex. Crystallographic analysis suggested that the neutralizing epitope overlapped with the MHC II molecule binding site on SEB, and thus 3E2 could inhibit SEB function by preventing interaction with the MHC II molecule. Mutagenesis studies were done on SEB, as well as the related Staphylococcus aureus toxins SEA and SEC. These studies revealed that tyrosine (Y)46 and lysine (K)71 residues of SEB are essential to specific antibody-antigen recognition and neutralization. Substitution of Y at SEA glutamine (Q)49, which corresponds to SEB Y46, increased both 3E2's binding to SEA in vitro and the neutralization of SEA in vivo. These results suggested that SEB Y46 is responsible for distinguishing SEB from SEA. These findings may be helpful for the development of antibody-based therapy for SEB-induced TSS.

3,3'-Diindolylmethane Ameliorates Staphylococcal Enterotoxin B-Induced Acute Lung Injury through Alterations in the Expression of MicroRNA that Target Apoptosis and Cell-Cycle Arrest in Activated T Cells

“…SEB exposure drives extensive release of chemokines and cytokines, T-cell expansion, and both localized and systemic tissue damage (Krakauer, 1999;Saeed et al, 2012;Busbee et al, 2014). This atypical immune response can be attributed to the unique mechanism of T-cell activation that SEB uses, expanding a considerable proportion of T cells by binding sequentially the vb8 region of the TCR on T cells and major histocompatibility class II molecule on antigen presenting cells (Herman et al, 1991;Xia et al, 2014). Our results are consistent with these findings, as we observed a dramatic increase in infiltrating mononuclear cells and significant endothelial-epithelial barrier destruction in the lungs.…”

Engineered pH-dependent recycling antibodies enhance elimination of Staphylococcal enterotoxin B superantigen in mice

“…The measured affinity for wild type 3E2 (0.17 nM) closely matches a previously reported value (0.58 nM). 14 The PAR values obtained by measuring the K D at pH 7.4 and 6.0 remained largely unchanged from the estimates obtained using yeast displayed scFv, although the affinity was higher for full-length antibodies ( Table 2). 27,28 The affinity measurement was repeated by surface plasmon resonance (SPR), which showed similar pH-dependent binding by engineered antibodies (Table S1).…”

“…Using the crystal structure of a previously reported antibody 3E2 Fab in complex with SEB, 14 we selected 20 antibody residues that are within 4.5 Å of SEB, and targeted them for histidine mutation (Figure 2(a)). The antibody inhibits the activity of SEB by interfering with its interaction with MHC II on antigen-presenting cells (Fig.…”

“…SEB is secreted by methicillin-resistant Staphylococcus aureus (MRSA), and is a wellknown and sometimes fatal cause of sepsis in patients. MAbs against SEB has been engineered to inhibit SEB activity invitro [11][12][13][14][15][16] and in vivo, 17,18 and there are also some promising leads in developing vaccines against the molecule. 19,20 Still, there are challenges in developing an antibody-based treatment, and to our knowledge, no antibody-based therapy has been approved for clinical use to date.…”

Superantigen staphylococcal enterotoxin C1 inhibits the growth of bladder cancer

“…As superantigens, with homologous structures and functions, SEs can bind to MHC class II molecules and are presented to T cells which express appropriate variable part of β chain on T cell receptors (TCR). 8,9) As a result, SEs can cause an unusual stimulation to high percentage of T cell and initiate massively release of cytokines. 10) Due to this attribute, SEs are believed to be exploited in immunotherapy of a variety of malignant tumors.…”