PSMA4
Description
The PSMA4 (proteasome 20S subunit alpha 4) is a protein-coding gene located on chromosome 15.
Proteasome subunit alpha type-4, also known as macropain subunit C9, proteasome component C9, and 20S proteasome subunit alpha-3, is a protein that in humans is encoded by the PSMA4 gene. This protein is one of the 17 essential subunits (alpha subunits 1–7, constitutive beta subunits 1–7, and inducible subunits including beta1i, beta2i, beta5i) that contributes to the complete assembly of the 20S proteasome complex. The PSMA4 gene encodes a member of the peptidase T1A family, that is a 20S core alpha subunit. The gene has 9 exons and locates at chromosome band 15q25.1. The human protein proteasome subunit alpha type-4 is 29.5 kDa in size and composed of 261 amino acids. The calculated theoretical pI of this protein is 6.97. The proteasome is a multicatalytic proteinase complex with a highly ordered 20S core structure. This barrel-shaped core structure is composed of 4 axially stacked rings of 28 non-identical subunits: the two end rings are each formed by 7 alpha subunits, and the two central rings are each formed by 7 beta subunits. Three beta subunits (beta1, beta2, and beta5) each contains a proteolytic active site and has distinct substrate preferences. Proteasomes are distributed throughout eukaryotic cells at a high concentration and cleave peptides in an ATP/ubiquitin-dependent process in a non-lysosomal pathway.
PSMA4 is a component of the 20S core proteasome complex, which is involved in the breakdown of most proteins within cells. It associates with different regulatory particles to perform various essential cellular functions. When paired with two 19S regulatory particles, it forms the 26S proteasome, which breaks down ubiquitinated proteins in an ATP-dependent manner. This process is crucial for maintaining protein homeostasis by removing misfolded or damaged proteins and those that are no longer needed. PSMA4 can also associate with PA200 or PA28, allowing the 20S proteasome to degrade proteins without ubiquitination. This type of proteolysis is essential for processes like spermatogenesis (20S-PA200 complex) and generating specific MHC class I-presented antigenic peptides (20S-PA28 complex).
PSMA4 is also known as HC9, HsT17706, PSC9.
