PA28 Activator alpha Subunit: Proteins and Enzymes

The Proteasome Activator 28 (PA28) Regulatory Complex, also known as the 11S Regulatory (REG) Complex, is a ring-shaped, multimeric, ATP-independent regulatory complex that can bind to one or both ends of the 20S Proteasome or 20S Immunoproteasome. The PA28 Regulatory Complex stimulates the proteasome to hydrolyze small peptides, but not ubiquitinated proteins, for the production of peptides for MHC class I antigen presentation. Three PA28 Regulatory Complex subunits, alpha, beta, and gamma, have been identified and can oligomerize to form the PA28 Regulatory Complex. While the expression of the PA28 alpha and beta subunits are induced by IFN-gamma, PA28 gamma is not significantly affected.

The human PA28 Activator alpha Subunit, also known as 11S REG alpha, is a 249 amino acid (aa) member of the PA28 family of regulatory proteins with a predicted molecular weight of 28 kDa. The mouse and rat orthologs share 94% and 95% aa sequence identity with the human protein, respectively. In vivo, PA28 alpha forms hetero-heptamers or -hexamers with PA28 beta. PA28 alpha can also form active homo-heptamers in vitro and can be used to activate the 20S Proteasome. In addition to regulating production of MHC class I antigens, PA28 alpha may protect against oxidative stress.