Proteasome subunit alpha type-5

PSMA5 (proteasome subunit alpha type-5) is a core structural component of the 20S proteasome complex, which mediates ATP-dependent degradation of ubiquitinated proteins when associated with 19S regulatory particles to form the 26S proteasome (UniProt: P28066). The protein also participates in ubiquitin-independent proteolysis when associated with PA200 or PA28 regulatory particles, contributing to processes including spermatogenesis and MHC class I antigen presentation. As a central component of the proteasomal degradation machinery, PSMA5 is essential for maintaining protein homeostasis by removing misfolded, damaged, or functionally obsolete proteins.

PSMA5 is a ubiquitously expressed proteasomal subunit involved in intracellular protein quality control across multiple cellular contexts. No baseline disease associations are noted in UniProt for this protein.

In Alzheimer's disease, PSMA5 is significantly downregulated in post-mortem AD brain tissue compared to age-matched controls (mean log2FC = −0.486; Chaparral AD proteomics). This downregulation was detected in human post-mortem AD brain using TMT-labeled quantitative proteomics across subcellular fractions. Reduced proteasomal capacity may impair the clearance of aggregation-prone proteins implicated in neurodegeneration, potentially contributing to the pathological protein accumulation characteristic of AD.