Proteasome subunit beta type-4, also known as PSMB4, belonged to the peptidase T1B family. The 20S Proteasome chamber contains alpha subunits (which are structural) and beta subunits (which are predominantly catalytic). The outer two rings in the proteasome consist of seven alpha subunits each and the inner two rings each consist of seven beta subunits. PSMB4 is a beta subunit of the 20S Proteasome.