26S proteasome non-ATPase regulatory subunit 9

PSMD9 (26S proteasome non-ATPase regulatory subunit 9) is a chaperone protein that facilitates assembly of the 26S proteasome, specifically functioning within the PA700/19S regulatory complex. During base subcomplex formation, PSMD9 transiently associates with PSMC6 and PSMC3 in a modulator trimer complex before being released during subsequent assembly steps (UniProt: O00233).

The protein operates within the ubiquitin-proteasome system, a central degradation pathway active across tissues. No primary disease associations are documented in UniProt curated records.

PSMD9 has been tagged for Alzheimer's Disease relevance based on proteomics profiling (Chaparral AD proteomics). In human post-mortem AD brain versus age-matched controls, PSMD9 showed ambiguous regulation across subcellular fractions (mean log2FC 0.2364), with detection in 2 of 4 fractions (P2, P3, S2, S3) in TMT-labeled, data-dependent acquisition proteomics. The modest, inconsistent fold-change and fractional distribution suggest no clear directional dysregulation in AD pathology, though subcellular redistribution cannot be excluded.