Immunoproteasome
From Wikipedia, the free encyclopedia
An immunoproteasome is a type of proteasome that degrades ubiquitin-labeled proteins found in the cytoplasm in cells exposed to oxidative stress and proinflammatory stimuli. In general, proteasomes consist of a regulatory and a catalytic part. Immunoproteasomes are induced by interferon gamma (but also by other proinflammatory cytokines) and oxidative stress, which in the cell triggers the transcription of three catalytic subunits that do not occur in the classical proteasome.[1] Another possible variation of proteasome is the thymoproteasome, which is located in the thymus and folds to present peptides to naive T cells.
Structurally, immunoproteasome is a cylindrical protein complex composed of a catalytic 20S subunit and a 19S regulatory subunit. The catalytic subunit consists of four outer alpha rings and four inner beta rings.[2] In the classical proteasome, the beta (β) 1, β2 and β5 subunits have catalytic activity, which, however, in the immunoproteasome are replaced by the subunits LMP2 (alias β1i), MECL-1 (alias β2i), and LMP7 (alias β5i).[3] The LMP2 protein is composed of 20 amino acids, MECL-1 of 39 amino acids and LMP7 occurs in isoform and therefore can have either 72 or 68 amino acids.[1] The regulatory unit consists of 19 proteins, which are structurally divided into a lid of 9 proteins and a base again of 9 proteins. The RPN10 protein is added to this regulatory complex, which serves to stabilize the structure and as a receptor for ubiquitin.[4]