Cold Denaturation of Proteins in the Absence of Solvent: Implications for Protein Storage

The effect of temperature on the stability of proteins is well explored above 298K, but harder to track experimentally below 273K. Variable temperature ion mobility mass spectrometry (VT IM-MS) allows us to measure the structure of molecules at sub-ambient temperatures. Here we monitor conformational changes that occur to two isotypes of monoclonal antibodies (mAbs) on cooling by measuring their collision cross sections (CCS) at discrete drift gas temperatures from 295 to 160K. The CCS at 250K is larger than predicted from collisional theory and experimental data at 295K. This restructure is attributed to change in the strength of stabilizing intermolecular interactions. Below 250K the CCS of the mAbs increases in line with prediction implying no rearrangement. Comparing data from isotypes suggest disulfide bridging influences thermal structural rearrangement. These findings indicate that in vacuo deep-freezing minimizes denaturation and maintains the native fold and VT IM-MS measurements at sub ambient temperatures provide new insights to the phenomenon of cold denaturation.