Component of the lid subcomplex of the 26S proteasome, a multiprotein complex involved in the ATP-dependent degradation of ubiquitinated proteins. In the complex, psmD11 is required for proteasome assembly (By similarity). Component of the lid subcomplex of the 19S proteasome regulatory particle complex (also named PA700 complex). The 26S proteasome consists of a 20S proteasome core and two 19S regulatory subunits (By similarity). Belongs to the proteasome subunit S9 family.