Elucidating allosteric processes in immunoglobulin E (360G-Wellcome-211846_Z_18_Z)

Immunoglobulin E (IgE) is thought to be the first line of defence against parasitic pathogens, mediating immune reactions by binding to either of its two receptors, either the high-affinity FcepsilonRI receptor or the low-affinity CD23 receptors. While the IgE molecule was previously thought to exist in a primarily acutely bent conformation in solution, Drinkwater et al. (2014) found that IgE was able to exist in a fully extended conformation while Davies et al (2017) showed that omalizumab (XolairTM by Novartis) trapped IgE in a partially bent state to block its action on its FcepsilonRI receptors. The McDonnell Laboratory has derived a series of anti-IgE antibody Fab fragments, selected for their ability to affect IgE’s overall structure and dynamics and consequently to allosterically affect the binding to IgE’s receptors. In this proposed study, we will investigate how observed ligand-mediated changes in conformational dynamics manifest themselves as entropically-driven allosteric modulation. As a complement to NMR studies of ligand-mediated changes in protein dynamics, currently ongoing in the McDonnell Laboratory, direct measurements of the thermodynamic parameters of ligand binding will be performed using isothermal titration calorimetry.