InterPro domain: IPR034647

The proteasome (or macropain) ( 3.4.25.1 ) [ 1 , 2 , 3 , 4 , 5 ] is a multicatalytic proteinase complex in eukaryotes and archaea, and in some bacteria, that is involved in an ATP/ubiquitin-dependent non-lysosomal proteolytic pathway. In eukaryotes the 20S proteasome is composed of 28 distinct subunits which form a highly ordered ring-shaped structure (20S ring) of about 700kDa. Proteasome subunits can be classified on the basis of sequence similarities into two groups, alpha (A) and beta (B). The proteasome consists of four stacked rings composed of alpha/beta/beta/alpha subunits. There are seven different alpha subunits and seven different beta subunits [ 6 ]. Three of the seven beta subunits are peptidases, each with a different specificity. Subunit beta1c (MEROPS identifier T01.010) has a preference for cleaving glutaminyl bonds ("peptidyl-glutamyl-like" or "caspase-like"), subunit beta2c (MEROPS identifier T01.011) has a preference for cleaving arginyl and lysyl bonds ("trypsin-like"), and subunit beta5c (MEROPS identifier T01.012) cleaves after hydrophobic amino acids ("chymotrypsin-like") [ 7 ]. The proteasome subunits are related to N-terminal nucleophile hydrolases, and the catalytic subunits have an N-terminal threonine nucleophile.

This entry includes the non-enzymatic subunit alpha4 of the 19S proteasome complex (MEROPS identifier T01.973). The equivalent subunit in is known confusingly as alpha3 in species such as Saccharomyces cerevisiae . The alpha4 and alpha7 subunits interact via their N termini [ 8 ]. The alpha4 subunit is replaced by the alpha4s subunit in germ cells that enter meiotic prophase [ 9 ]. In Drosophila melanogaster , there are two additional testis-specific alpha4 subunits (known as alpha 7-1A and alpha-7-1B) [ 10 ].

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