Inhibition of the 26S and 20S Proteasomes by the Site-specific Inhibitors

ABSTRACT

OBJECTIVE: The study was performed to establish the purification processes of both 26S and 20S proteasomes, also to investigate the inhibitory properties and patterns of two different proteasome inhibitors on the isolated proteasomes. METHODS: The 26S and 20S proteasomes were purified respectively using liquid chromatographies and glycerol density gradient fractionation. The inhibitory patterns and kinetics of two different proteasome inhibitors were investigated using purified 26S and 20S proteasomes. RESULTS: The purity of the isolated proteasomes were determined by their biochemical properties and electrophoretic patterns. 3-nitro-4-hydroxy-5-indophenylacetyl-leucyl-leucyl-leucyl-vinylsulfone (Nip-L₃-VS) inhibited exclusively the chymotrypsin-like peptidase activities of the 26S and 20S proteasomes. On the other hand, dansyl-phenylyl-leucyl-boronic acid (DFLB) inhibited chymotrpsin-like, trypsin-like, and caspase-like peptidase activities of both proteasomes with different sensitivity. CONCLUSION: The proposed purification method provides efficient separation and isolation of the 26S and 20S proteasomes. Nip-L₃-VS and DFLB were shown to have different inhibitory effects and kinetics on the peptidase activities of the isolated proteasomes. These studies are suggested to be applied to the researches on proteasome inhibitors as therapeutic reagents for many related diseases.