Integrative structural biology approaches make use of artificial intelligence-assisted modelling on one side and of experimental analyses on the other for in-depth characterization of higher order protein structures as well as physiological structural changes. Calculations of CCS values are based on either three-dimensional (3D) protein structures or 3D structure models, resembling protein structures in condensed phase. Measuring collision cross sections (CCS) of proteins by nano-electrospray mass spectrometry is rapidly performed with consuming only little material and provides CCS of protein ions in the gas phase. Interestingly, calculated and experimentally determined CCS match well as long as 3D structures show that peptides, proteins, and complexes are compactly folded. Hence, gas phase CCS values provide useful information about higher order solution structures. Deviations between gas phase CCS values and those from compact 3D solution structures are found as well and lend evidence that in solution such shapeshifting proteins adopt more than one conformation.