A conformation-specific approach to native top-down mass spectrometry

Native top-down mass spectrometry is a powerful approach for characterizing proteoforms, and has recently been applied to provide similarly powerful insights into protein conformation. Current approaches, however, are limited such that struc-tural insights can only be obtained for the entire conformational landscape in bulk, or without any direct conformational measurement. We report a new ion mobility-enabled method for performing native top-down MS in a conformation-specific manner. Our approach identified conformation-linked differences in backbone dissociation for the model protein calmodulin, which simultaneously inform upon proteoform variations and provide structural insights. We also illustrate that our method can be applied to protein-ligand complexes, either to identify components or to probe ligand-induced structural changes.