BAG family molecular chaperone regulator 5

BAG5 (BAG family molecular chaperone regulator 5) is a co-chaperone protein that acts as a nucleotide-exchange factor for HSP70 family chaperones, promoting the release of ADP and thereby activating HSP70-mediated protein refolding (UniProt: Q9UL15). The protein maintains proteostasis at junctional membrane complexes and inhibits parkin-mediated ubiquitination, playing roles in both protein quality control and mitochondrial dynamics.

BAG5 is expressed across tissues and has been associated with autosomal recessive dilated cardiomyopathy (CMD2F, MIM 619747) in UniProt curated disease records (UniProt: Q9UL15). Its function in chaperone-mediated proteostasis suggests broader relevance to neurodegenerative contexts.

In Alzheimer's disease, BAG5 is downregulated in post-mortem AD brain tissue compared to age-matched controls (Chaparral AD proteomics), with a mean log2 fold-change of −0.96. This reduction was detected in a single subcellular fraction using TMT-labeled quantitative proteomics, suggesting potential impairment of HSP70-dependent protein refolding capacity in AD pathology.