Structural Analysis of the 20S Proteasome Using Native Mass Spectrometry and Ultraviolet Photodissociation

Owing to the role of the 20S proteasome in a wide spectrum of pathologies, including neurodegenerative disorders, proteasome-associated autoinflammatory syndromes (PRAAS), and cardiovascular diseases, understanding how its structure and composition contribute to dysfunction is crucial. As a 735 kDa protein assembly, the 20S proteasome facilitates normal cellular proteostasis by degrading oxidized and misfolded proteins. Declined proteasomal activity, which can be attributed to perturbations in the structural integrity of the 20S proteasome, is considered one of the main contributors to multiple proteasome-related diseases. Devising methods to characterize the structures of 20S proteasomes provides necessary insight for the development of drugs and inhibitors that restore proper proteasomal function. Here, native mass spectrometry was combined with multiple dissociation techniques, including ultraviolet photodissociation (UVPD), to identify the protein subunits comprising the 20S proteasome. UVPD, demonstrating an ability to uncover structural features of large (>300 kDa) macromolecular complexes, provided complementary information to conventional collision-based methods. Additionally, variable-temperature electrospray ionization was combined with UV photoactivation to study the influence of solution temperature on the stability of the 20S proteasome.