Collisional and Coulombic unfolding of gas-phase proteins: high correlation to their domain structures in solution

The three-dimensional structures adopted by proteins are predicated by their many biological functions. Mass spectrometry has played a rapidly expanding role in protein structure discovery, enabling the generation of models for both proteins and their higher-order assemblies. While important coursed-grained insights have been generated, relatively few examples exist where mass spectrometry has been successfully applied to the characterization of protein tertiary structure. Here, we demonstrate that gas-phase unfolding can be used to determine the number of autonomously folded domains within monomeric proteins. Our ion mobility-mass spectrometry data highlight a strong, positive correlation between the number of protein unfolding transitions observed in the gas phase and the number of known domains within a group of sixteen proteins ranging from 8-78 kDa. This correlation and its potential uses for structural biology is discussed.