(180j) Conformational Orientation of Monoclonal Antibody at the Air-Water Interface

Protein molecules are surface active and therefore adsorb onto air/water interfaces. This adsorption has been studied for several proteins – particularly globular ones – which are known to unfold at the interface to expose hydrophobic residues. Here, we study the adsorption of monoclonal antibodies (mAbs) on an air/water interface. The confined, “Y” shaped structure, of mAbs, provides a contrast in their adsorption behavior to the globular proteins. Using a combination of X-ray reflectivity (XR) and computational simulations, we demonstrate how mAb molecules orient themselves at the air-water interface as a function of concentration. We find two principal states of adsorption, “flat-on” at low concentrations and “side-on” at high concentrations. We use computational simulations to further interpret the electron density profiles obtained by XR and confirm these two states. We demonstrate, using pendant bubble tensiometry, that these two states define the dynamic tension relaxation of the mAbs as they adsorb to a clean air/water interface. For early times, an induction period is observed which is interpreted as a phase transition between gaseous and liquid “flat-on” states. With continued adsorption, the tension drops dramatically corresponding to an increased packing of the mAbs and a reorientation to “side-on” configuration. Our multidisciplinary approach has helped to provide a mechanistic atomic-level detail for the first time to uncover the general understanding of antibody interfacial behavior at the air-water interface.