Structure and properties of the 26S protease complex from chick skeletal muscle

Abstract

The 26S protease complex was purified from chick skeletal muscle and shown to consist of unusually heterogeneous 21-140 kDa polypeptides, including the 21-32 kDa subunits of the 20S proteasome. Electron microscopic analysis revealed that the 26S complex may have a symmetric morphology with two large rectangular terminal domains attached to a thinner central 20S proteasome domain. The 26S complex was capable of degrading the peptide substrates of the 20S proteasome, including Suc-LLVY-AMC, N-Cbz-LLE-NA and N-Cbz-ARR-MNA. The two enzyme complexes showed similar sensitivities to various site-specific protease inhibitors, although their sensitivities to SDS were differed from each other. Immunoprecipitation with anti-26S complex antibody reduced peptide hydrolysis by the 20S proteasome. Similarly, anti-20S proteasome antibody inhibited peptide hydrolysis by the 26S complex. These results demonstrate that the 26S protease complex contains the 20S proteasome as a functional and structural component.