 The subunit beta5i only presents in the immunoproteasome and is replaced by subunit beta5(proteasome beta 5 subunit) in constitutive 20S proteasome complex.This protein has an important function in the immune system as part of an immunoproteasome which possess specific cleavage properties that aid in the release of peptides necessary for MHC class I antigen presentation.The proteasome and its subunits are of clinical significance for at least two reasons