Mapping the interactions of selective biochemical probes of antibody conformation by hydrogen‐deuterium exchange mass spectrometry

Protein-based pharmaceuticals represent the fastest growing group of drugs in development in the pharmaceutical industry. One of the major challenges in the discovery, development, and distribution of biopharmaceuticals is the assessment of changes in their higher-order structure due to chemical modification. Here, we investigated the interactions of three different biochemical probes (Fabs) generated to detect conformational changes in a therapeutic IgG1 antibody (mAbX) by local hydrogen-deuterium exchange mass spectrometry (HDX-MS). We show that two of the probes target the Fc part of the antibody, whereas the third probe binds to the hinge region. Through HDX-ETD, we could distinguish specific binding patterns of the Fc-binding probes on mAbX at the amino-acid level. Preliminary surface plasmon resonance (SPR) experiments showed that these domain-selective Fab probes are sensitive to conformational changes in distinct regions of a full-length therapeutic antibody upon oxidation.