The stability of wild-type and deletion mutants of human C-terminus Hsp70-interacting protein (CHIP)

Carboxyl terminus of Hsp70 interacting protein (CHIP) is a dimeric co-chaperone involved in providing an appropriate balance between the synthesis and degradation of proteins, which is essential for normal cellular growth and function. Previous work has shown that CHIP, but not its isolated domains, has chaperone activity that is enhanced by heat. In this work, we investigate how heat and urea affect the stability of its domains. We found that the deletion mutant containing the TPR domain, which binds to chaperones Hsp70 or Hsp90, was monomeric and showed similar folding and stability to WT, while the mutant containing the U-box ubiquitin ligase domain was dimeric but had very low stability. The deletion mutants appeared to maintain most of their structure compared to the WT protein, but the regions around the tryptophan residues, which are at the interface of the domains in the WT structure, appeared to be more unfolded, which indicated that the region of contact between domains is likely important for the chaperone function.