Figure 5: Inhibition of WT and mutant β5-T1S proteasomes by bortezomib and carfilzomib.
From: A unified mechanism for proteolysis and autocatalytic activation in the 20S proteasome
Inhibition assays (left panel). Purified yeast proteasomes were tested for the susceptibility of their ChT-L (β5) activity to inhibition by bortezomib and carfilzomib using the substrate Suc-LLVY-AMC. IC50 values were determined in triplicate; s.d.’s are indicated by error bars. Note that IC50 values depend on time and enzyme concentration. Proteasomes (final concentration: 66 nM) were incubated with inhibitor for 45 min before substrate addition (final concentration: 200 μM). Structures of the β5-T1S mutant in complex with both ligands (green) prove the reactivity of Ser1 (right panel). The 2FO–FC electron-density maps (blue mesh) for Ser1 (brown) and the covalently bound ligands (green; only the P1 site (Leu1) is shown) are contoured at 1σ. The WT proteasome:inhibitor complex structures (inhibitor in grey; Thr1 in black) are superimposed and demonstrate that mutation of Thr1 to Ser does not affect the binding mode of bortezomib or carfilzomib.
