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. 2013 Feb 1;8(2):e52408. doi: 10.1371/journal.pone.0052408

Figure 6. Summary model – the 11S activates the immunoproteasome in response to reduced ATP levels.

Figure 6

In pancreatic β-cells exposed to IFNs, early immunoproteasome 20S cores have stochastic combinations of regular and immune proteolytic subunits, and coexist with the 19S and 11S activators. However, only under conditions of ATP depletion the proteolytic rates are stimulated in a manner consistent with the levels of the 11S activator. Two mechanisms could explain this observation. (A). The 20S cores could be saturated with the ATP-dependent 19S activators, and the 11S would bind the 20S cores only when at least one of the two 19S complexes dissociates in a manner stimulated by low ATP. (B). The 11S could be incorporated into hybrid 19S/20S/11S particles, but their proteolytic function would depend primarily on the 19S activator until ATP concentrations drop. Question mark emphasizes that it is unclear whether the final, 11S-activated immunoproteasome lacks the 19S activator. See text for details.