Complementary Structural Information for Stressed Antibodies from Hydrogen-Deuterium Exchange and Covalent Labeling Mass Spectrometry.

Identifying changes in the higher-order structure (HOS) of therapeutic monoclonal antibodies upon storage, stress, or mishandling is important for ensuring efficacy and avoiding adverse effects. Here, we demonstrate diethylpyrocarbonate (DEPC)-based covalent labeling (CL) mass spectrometry (MS) and hydrogen-deuterium exchange (HDX)/MS can be used together to provide site-specific information about subtle conformational changes that are undetectable by traditional techniques. Using heat-stressed rituximab as a model protein, we demonstrate that CL/MS is more sensitive than HDX/MS to subtle HOS structural changes under low stress conditions (e.g., 45 and 55 °C for 4 h). At higher heat stress (65 °C for 4 h), we find CL/MS and HDX/MS provide complementary information, as CL/MS reports on changes in side chain orientation while HDX/MS reveals changes in backbone dynamics. More interestingly, we demonstrate that the two techniques work synergistically to identify likely aggregation sites in the heat-stressed protein. In particular, the C and C domains experience decreases in deuterium uptake after heat stress, while only the C domain experiences decreases in DEPC labeling extent as well, suggesting the C domain is a likely site of aggregation and the C domain only undergoes a decrease in backbone dynamics. The combination of DEPC-CL/MS and HDX/MS provides valuable structural information, and the two techniques should be employed together when investigating the HOS of protein therapeutics.