Structure and assembly of the 20S proteasome.

The barrel-shaped 20S proteasome is one of the two components of a larger 26S particle, the multicatalytic 2000-kDa protease complex. The proteolytic sites are located in the inner chamber of the 20S particle and are only accessible via narrow entrances. This paper reviews the current knowledge concerning proteasome formation, proteolytic activities, structural aspects and assembly.

The human proteasomal subunit HsC8 induces ring formation of other alpha-type subunits.

The eukaryotic 20 S proteasome is a barrel-shaped protease complex, made up of four seven-membered rings. The outer and inner rings contain seven different alpha and beta-type subunits, respectively, each subunit located at a defined position. Recently, we have reported that the recombinant human alpha-type subunit C8 (HsC8) assembles into a heptameric ring-like structure by itself.

Detailed analysis of cell cycle kinetics upon proteasome inhibition.

We have studied specific effects of proteasome inhibition on cell cycle progression. To this end, the protease inhibitors MG115, calpain inhibitor I, and calpain inhibitor II, which display differential inhibitory effects on proteasomes, were used. Cell kinetic studies using bromodeoxyuridine pulse labeling revealed a complete block of G1/S and metaphase transitions and a delayed progression through S phase in cell cultures treated with 54 microM of MG115.

The human alpha-type proteasomal subunit HsC8 forms a double ringlike structure, but does not assemble into proteasome-like particles with the beta-type subunits HsDelta or HsBPROS26.

The eukaryotic proteasome is a barrel-shaped protease complex made up of four seven-membered rings of which the outer and inner rings may contain up to seven different alpha- and beta-type subunits, respectively. The assembly of the eukaryotic proteasome is not well understood. We cloned the cDNA for HsC8, which is one of the seven known human alpha-type subunits, and produced the protein in Escherichia coli.

Reduced chaperone-like activity of alpha A(ins)-crystallin, an alternative splicing product containing a large insert peptide.

alpha-Crystallin is a multimeric protein complex which is constitutively expressed at high levels in the vertebrate eye lens, where it serves a structural role, and at low levels in several non-lenticular tissues. Like other members of the small heat shock protein family, alpha-crystallin has a chaperone-like activity in suppressing nonspecific aggregation of denaturing proteins in vitro. Apart from the major alpha A- and alpha B-subunits, alpha-crystallin of rodents contains an additional minor subunit resulting from alternative splicing, alpha A(ins)-crystallin.