E3 ubiquitin-protein ligase UBR1

UBR1 is an E3 ubiquitin-protein ligase that functions as a core component of the N-end rule pathway (UniProt: Q8IWV7). It recognizes and binds proteins bearing destabilizing N-terminal residues (N-degrons) and catalyzes their ubiquitination and degradation. UBR1 distinguishes between type-1 degrons (positively charged residues) and type-2 degrons (bulky hydrophobic amino acids), and also negatively regulates the leucine-mTOR signaling pathway to control cell growth.

Mutations in UBR1 are associated with Johanson-Blizzard syndrome, a disorder characterized by congenital pancreatic insufficiency, craniofacial malformations, and intellectual disability (UniProt: Q8IWV7). The role of UBR1 in protein quality control and growth signaling suggests involvement in neurobiological processes relevant to neurological function.

UBR1 is downregulated in Alzheimer's disease brain tissue (Chaparral AD proteomics). Analysis of post-mortem AD brain versus age-matched controls using TMT-labeled proteomics across four subcellular fractions revealed a mean log2 fold-change of −1.52, indicating reduced UBR1 abundance in the disease state. This downregulation may reflect impaired protein quality control mechanisms in AD pathology.