Alternative titles; symbols
HGNC Approved Gene Symbol: PSMB7
Cytogenetic location: 9q33.3 Genomic coordinates (GRCh38): 9:124,353,465-124,415,442 (from NCBI)
The 20S (700-kD) proteasome, which contains multiple peptidase activities, is one component of the 26S (2000-kD) complex, which degrades ubiquitinated proteins. The 20S proteasome is composed of alpha and proteolytic beta subunits. See PSMB2 (602175). One important function of the proteasome in higher vertebrates is to generate the peptides presented on MHC-class 1 molecules to circulating lymphocytes. The cytokine gamma-interferon (IFNG; 147570), which stimulates antigen presentation, alters proteasome subunit composition and functional activity. Upon IFNG treatment, the beta subunits X (600306) and Y (600307) are replaced by subunits LMP7 (177046) and LMP2 (177045), respectively. The changes in peptidase activity are due to the incorporation of the LMP subunits (Coux et al. (1996)).
Hisamatsu et al. (1996) determined that a third pair of proteasome subunits, Z and MECL1 (176847), are expressed reciprocally in response to IFNG treatment. Z is downregulated, while MECL1 is markedly induced, suggesting that Z can be replaced by MECL1 in the proteasomal complex. By screening a HepG2 cell line library with a probe based on the partial amino acid sequence of the Z protein, the authors isolated cDNAs encoding Z. Sequence analysis revealed that the predicted 277-amino acid Z protein is a beta subunit. Z shares 58% and 55% protein sequence identity with MECL1 and PUP1, a S. cerevisiae proteasomal subunit, respectively. Both Z and MECL1 are proteolytically processed to generate a mature protein with an N-terminal threonine residue that is required for activity.
Coux et al. (1996) stated that the IFNG-induced beta subunits MECL1, LMP7, and LMP2, likely alter peptidase activity because they contain distinct active sites. Thus the proteasomes from IFNG-treated cells should generate more peptides with hydrophobic or basic C termini, like the vast majority of peptides presented on MHC class I molecules. Hisamatsu et al. (1996) proposed that 20S particles containing MECL1, LMP7, and LMP2 be designated immunoproteasomes to emphasize their role in immunologic processing of endogenous antigens.
By fluorescence in situ hybridization, Hisamatsu et al. (1996) mapped the Z gene to 9q34.11-q34.12.
Coux, O., Tanaka, K., Goldberg, A. L. Structure and functions of the 20S and 26S proteasomes. Ann. Rev. Biochem. 65: 801-847, 1996. [PubMed: 8811196] [Full Text: https://doi.org/10.1146/annurev.bi.65.070196.004101]
Hisamatsu, H., Shimbara, N., Saito, Y., Kristensen, P., Hendil, K. B., Fujiwara, T., Takahashi, E., Tanahashi, N., Tamura, T., Ichihara, A., Tanaka, K. Newly identified pair of proteasomal subunits regulated reciprocally by interferon gamma. J. Exp. Med. 183: 1807-1816, 1996. [PubMed: 8666937] [Full Text: https://doi.org/10.1084/jem.183.4.1807]