The proteasome is a multicatalytic proteinase complex which is characterized by its ability to cleave peptides with Arg, Phe, Tyr, Leu, and Glu adjacent to the leaving group at neutral or slightly basic pH. The proteasome has an ATP-dependent proteolytic activity. This subunit is involved in antigen processing to generate class I binding peptides. Contributes to NFKBIA degradation and subsequently NFKB1 generation. Cleavage of peptide bonds with very broad specificity. The 26S proteasome consists of a 20S proteasome core and two 19S regulatory subunits. The 20S proteasome core is composed of 28 subunits that are arranged in four stacked rings, resulting in a barrel-shaped structure. The two end rings are each formed by seven alpha subunits, and the two central rings are each formed by seven beta subunits. The catalytic chamber with the active sites is on the inside of the barrel. Component of the immunoproteasome, where it displaces the equivalent housekeeping subunit PSMB6. Component of the spermatoproteasome, a form of the proteasome specifically found in testis. Interacts with NCOA1, NCOA2 and NCOA3. Detected in liver (at protein level). Expressed at high levels in the thymus, spleen, lung, heart and liver. Expressed at moderate levels in the kidney. Up-regulated by interferon gamma (at protein level). Up-regulated by IRF1. Up-regulated by heat shock treatment. Down-regulated by EGR1 in neuronal cells. Autocleaved. The resulting N-terminal Thr residue of the mature subunit is responsible for the nucleophile proteolytic activity. Depletion of LMP2 by RNAi suppresses expression and activities of the matrix metalloproteinase MMP2 and MMP9 by blocking the transfer of active NF-kappa-B heterodimers into the nucleus. Belongs to the peptidase T1B family.