Mapping Binding Epitopes and Allosteric Effects in Staph Enterotoxins

Abstract

Staphylococcal enterotoxins (SEs) cause food poisoning-like symptoms and can be lethal at microgram amounts. SEs elicit profound immune responses via the bridging of major histocompatibility complex class II (MHCII) molecules on antigen presenting cells with T-cell receptors (TCR). 20B1, 14G8, and 6D3 stand out as promising neutralizing monoclonal antibodies (mAbs) that have been co-crystalized with staphylococcus enterotoxin B (SEB). Although crystal structures have been solved with SEB and a variety of antibodies, it is still not understood why some antibodies effectively neutralize toxins while others do not. Paired with structures of MHC class II and TCR bound to SEB, it has been suggested that 20B1 inactivates SEB by sterically hindering the binding of the toxin to immune molecules. 14G8 and 6D3 also inactivate SEB, but through binding interactions at distal epitopes. Using Hydrogen Deuterium Exchange coupled to Mass Spectrometry (HDX-MS) and X-Ray Footprinting (XRF) in tandem with MS experiments, we observe that neutralizing antibodies binding to distal epitopes elicit allosteric effects in SEB that may drive neutralization.