Modulation of CHIP‐mediated degradation through posttranslational modifications

Abstract

Interactions between CHIP (C-terminus of Hsp70 Interacting Protein) and Hsp70 (70-kilodalton heat shock protein) promote CHIP-mediated degradation of misfolded proteins (clients) via the ubiquitin proteasome pathway. Modulating interactions of Hsp70 with either CHIP or HOP (Hsp Organizing Protein) controls misfolded protein turnover by shunting misfolded client proteins to either the degradative pathway or the refolding pathway. Differential affinity of Hsp70 for the tetratricopeptide repeat (TPR) domains of CHIP and HOP, which is responsible for the observed modulation, is achieved through interactions with the six residues preceding the carboxy-terminal Asp641 of Hsp70. In particular, phosphorylation of Hsp70 Thr636 produces a dramatic swing in binding affinities that shift preferential formation of CHIP/Hsp70 complexes to preferential formation of HOP/Hsp70 complexes. Thus, phosphorylation of Hsp70 Thr636 acts as a switch that modulates the response to protein misfolding and the ability for CHIP to degrade misfolded proteins via the ubiquitin-proteasome system. Herein, through biophysical assays and new structures of CHIP-Hsp70 and HOP-Hsp70 we identify the molecular mechanism that enables phosphorylation-driven switching that regulates protein degradation through CHIP-mediated ubiquitination. We also present a structure-guided mutation of CHIP that bypasses Thr636 phosphorylation-driven switching by recovering affinity of CHIP for phosphorylated Hsp70, thereby redirecting Hsp70 to preferentially bind to CHIP and directing misfolded protein clients toward degradation. This structure-guided mutation corrects a binding defect present in wild type CHIP and provides a system for studying the effect of shifting output of the CHIP-Hsp70/HOP-Hsp70 complexes toward chaperoned ubiquitination via CHIP. Support or Funding Information NIH R35 GM128595, NSF 15–52113 A structure-guided mutation restores affinity of CHIP for pThr636Hsp70 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.