STUP1/CHIP Protein, Human

STUB1 (STIP1 Homology and U-Box Containing Protein 1), commonly known as CHIP (C-terminus of Hsc70 Interacting Protein), is a crucial dual-function protein in cellular proteostasis. It serves as both a co-chaperone and an E3 ubiquitin ligase. As a co-chaperone, it binds to the molecular chaperones Hsp70/Hsc70 and Hsp90 via its N-terminal tetratricopeptide repeat (TPR) domain, assisting in client protein folding and stabilization. Its central role lies in its C-terminal U-box domain, which confers E3 ubiquitin ligase activity. This unique combination allows CHIP to ubiquitinate misfolded or damaged client proteins that are delivered by the chaperones, thereby targeting them for proteasomal degradation. It is a central component of the Protein Quality Control (PQC) system, clearing toxic protein aggregates and maintaining proteome integrity.

Dysregulation of CHIP function is linked to various human diseases. Loss-of-function mutations or reduced expression are associated with neurodegenerative disorders (e.g., spinocerebellar ataxia, Alzheimer's, Parkinson's) due to defective clearance of pathogenic proteins like tau and α-synuclein. Conversely, its role in degrading oncogenic clients (e.g., HER2, c-Myc) positions it as a potential tumor suppressor in certain cancers. It also plays key roles in aging, cardiac function, and immune responses, making it a significant therapeutic target.