Ubiquitin-like protein 4A

UBL4A (Ubiquitin-like protein 4A) is a 157-amino acid protein that functions as a core component of the BAG6/BAT3 cytosolic quality control complex. This complex maintains misfolded proteins in soluble states and directs them either to the endoplasmic reticulum for proper delivery or to the proteasome for degradation (UniProt: P11441). UBL4A participates in the post-translational delivery of tail-anchored proteins to the ER membrane, working alongside SGTA and ASNA1 to recognize newly synthesized transmembrane proteins at the ribosome. The BAG6/BAT3 complex also mediates ER-associated degradation (ERAD) and sorting of mislocalized secretory pathway proteins.

UBL4A is curated as relevant to Alzheimer's Disease. In human post-mortem AD brain tissue compared to age-matched controls, UBL4A is down-regulated (mean log2FC: −0.45) in TMT-labeled proteomics analysis across subcellular fractions (Chaparral AD proteomics). The functional role of UBL4A in protein quality control and ERAD suggests potential relevance to AD pathology, though the specific mechanistic implications of reduced UBL4A abundance in AD remain to be established.