Label-Free Quantitative Proteomics Reveals the Dynamics of Proteasome Complexes Composition and Stoichiometry in a Wide Range of Human Cell Lines

The proteasome is the main proteolytic system involved in intracellular proteins homeostasis in eukaryotes. Although the structure of proteasome complexes has been well characterized, the distribution of its activators and associated proteins are less studied. Here, we determine the composition and the stoichiometry of proteasome complexes and their associated proteins in a wide range of human cell lines using a one-step affinity purification method and a label-free quantitative proteomic approach. We show that proteasome complexes are highly dynamic protein assemblies, the activity of which being regulated at different levels by variations in the stoichiometry of bound regulators, in the composition of catalytic subunits and associated proteins, and in the rate of the 20S catalytic core complex assembly.