Understanding dry proteins and their protection with solid‐state hydrogen–deuterium exchange

Protein-based drugs are among our most powerful therapeutics, but their manufacture, storage, and distribution are hindered by solution instability and the expense of the necessary refrigeration. Formulating proteins as dry products, which is an almost entirely empirical endeavor, can ameliorate the problem, but recovery of an acceptable product upon resuspension is not always possible. Additional knowledge about dry protein structure and protection is necessary to make dry formulation both more rational and effective. While most biophysical and biochemical techniques necessitate solvated protein, solid-state hydrogen-deuterium exchange enables the study of dry proteins. Fourier-transform infrared spectroscopy, mass spectrometry, and liquid-observed vapor exchange nuclear magnetic resonance have all been used to measure isotopic exchange. These methods report on secondary structure, peptide, and residue level exposure, respectively. Recent studies using solid-state hydrogen-deuterium exchange provide insight into the mechanisms of dry protein protection and uncover stabilizing and destabilizing interactions, bringing us closer to rational formulation of these lifesaving products.