Protein Domain : Peptidase T1A, proteasome beta-subunit, archaeal IPR019983

Type	Family
Description	The proteasome (or macropain) ( ) [ , , , , ] is a multicatalytic proteinase complex in eukaryotes and archaea, and in some bacteria, that seems to be involved in an ATP/ubiquitin-dependent nonlysosomal proteolytic pathway. In eukaryotes the proteasome is composed of 28 distinct subunits which form a highly ordered ring-shaped structure (20S ring) of about 700kDa. Most proteasome subunits can be classified, on the basis on sequence similarities into two groups, alpha (A) and beta (B). These are arranged in four rings of seven proteins, consisting of a ring of alpha subunits, two rings of beta subunits, and a ring of alpha subunits. In eukaryotes, each alpha and each beta ring consists of different proteins. Three of the beta subunits are peptidases in subfamily T1A, and each has a distinctive specificity (trypsin-like, chymotrypsin-like and glutamyl peptidase-like). The peptidases are N-terminal nucleophile hydrolases in which the N-terminal threonine is the nucleophile in the hydrolytic reaction []. In the immunoproteasome, the catalytic components are replaced by three specialist, catalytic beta subunits []. In bacteria and archaea there is only one alpha subunit and one beta subunit, and each ring is a homoseptamer.This entry includes the beta subunit of the archaean proteasome (MEROPS identifier T01.002). The archaean proteasome consists of four stacked rings each of which contains a homoheptamer of either alpha or beta components, so that the rings are stacked in the order alpha, beta, beta, alpha. Alpha and beta subunits are homologous to one another, but only beta subunits are proteolytically active. The beta subunits are arranged so that the active sites are directed towards the centre of each ring. The proteasome is therefore a torus structure with a large cavity, and entrance and exit pores at the top and bottom. A dentured protein enters through the top pore, is degraded by the beta subunits into short peptides which exit from the bottom pore. The archaean proteasome is therefore similar to, but a simplified version of, the eukaryote proteasome. The crystal structure of the proteasome from Thermoplasma acidophylumwas the first to be solved, showing a structure similar to that of N-terminal nucleophile hydrolases [ ], and the beta subunit was found to be the first threonine peptidase [].
Short Name	Pept_T1A_Psome_bsu_arc