Biology subjects

Choy, W.-Y.

Publications and source records attributed to Choy, W.-Y..

4 recordsLinked to original sources

bioRxiv2026

TPR Domains Drive the Functional Phase Separation of HOP and its Regulation by Hsp90 and Hsp70

HOP is a cochaperone that facilitates client transfer between two major chaperones, Hsp90 and Hsp70. Emerging evidence, however, suggests that HOP plays additional roles in coordinating complex proteostasis networks. Upon exposure to proteostatic stress, HOP rapidly sequesters soluble misfolded proteins into cytoplasmic foci in a Hsp90 independent manner, thereby facilitating their clearance through the ubiquitin proteasome system. We demonstrate here that stress-dependent HOP foci are biomolecular condensates formed by liquid-liquid phase separation. Purified HOP forms protein droplets that closely resemble the foci observed in cells. Our biophysical analyses show that the phase separation of HOP is driven by electrostatic interactions between its tandem TPR domains, with a critical role of its TPR2A domain. Of note, Hsp90 and Hsp70 regulate the extent of HOP phase separation, with Hsp70 driving HOP droplet formation and Hsp90 reversing it. Finally, we find that the Y354E phosphomimetic variant of HOP impairs phase separation and sensitizes cells to acute misfolding stress, suggesting a key role of HOP condensation in mitigating protein misfolding stress. Our work thus identifies a new mechanism by which HOP phase separation mitigates protein misfolding stress in eukaryotic cells and is regulated by Hsp70 and Hsp90.

biochemistry↗

bioRxiv2025

STIP1/HOP Promotes the Formation of Cytotoxic α-Synuclein Oligomers

The accumulation of alpha-synuclein (a-Syn) as toxic oligomers, and subsequently in Lewy bodies, is a pathological hallmark of Parkinsons disease (PD) and other synucleinopathies. Molecular chaperones and co-chaperones are expected to act in concert to maintain physiological activities of proteins, including a-Syn, but in neurodegeneration this process can become mal-adaptive. Transcript levels of Stress inducible phosphoprotein 1 (STIP1), a co-chaperone of Hsp90/Hsp70, are elevated in brain samples from PD patients. In synucleinopathy mouse models, STIP1 has unexpected bidirectional effects on a-Syn, with overexpression of STIP1 aggravating a-Syn toxicity, whereas knockdown of STIP1 improves toxicity and behavioural phenotypes. However, it is unclear how STIP1 enhances the toxicity of a-Syn. Here we unravel the mechanisms by which the direct interaction between STIP1/HOP and a-Syn regulates the neurotoxicity of a-Syn. Specifically, two binding motifs in the C-terminus of a-Syn directly interact with the TPR2A domain of STIP1/HOP in a dynamic manner, competing for a shared interface on TPR2A. Binding of STIP1/HOP to a-Syn attenuates the formation of a-Syn fibrils while promoting the accumulation of high molecular weight amorphous a-Syn species. Samples of a-Syn aggregated in the presence of STIP1/HOP contain significantly more A11-positive oligomeric species and cause a greater reduction in cell viability than a-Syn aggregated in the absence of STIP1/HOP in neuronal cells. Our results provide a mechanism by which the direct interaction between STIP1/HOP and the C-terminus of a-Syn promotes the formation of cytotoxic, non-amyloidogenic, high molecular weight a-Syn species. Our model offers an explanation for the unexpected pathological link between STIP1 and a-Syn toxicity, thus opening new therapeutic avenues for the treatment of synucleinopathies.

biochemistry↗

bioRxiv2021

AlphaFold2: A role for disordered protein prediction?

The development of AlphaFold2 was a paradigm-shift in the structural biology community; herein we assess the ability of AlphaFold2 to predict disordered regions against traditional sequence-based disorder predictors. We find that a naaive use of Dictionary of Secondary Structure of Proteins (DSSP) to separate ordered from disordered regions leads to a dramatic overestimation in disorder content, and that the predicted Local Distance Difference Test (pLDDT) provides a much more rigorous metric. In addition, we show that even when used for disorder prediction, conventional predictors can outperform the pLDDT in disorder identification, and note an interesting relationship between the pLDDT and secondary structure, that may explain our observations, and hints at a broader application of the pLDDT to IDP dynamics.

bioinformatics↗

bioRxiv2018

A hypomorphic Stip1 allele reveals the requirement for chaperone networks in mouse development and aging

Chaperone networks are dysregulated with aging and neurodegenerative disease, but whether compromised Hsp70/Hsp90 chaperone function directly contributes to neuronal degeneration is unknown. Stress-inducible phosphoprotein-1 (STI1; STIP1; HOP) is a co-chaperone that simultaneously interacts with Hsp70 and Hsp90, but whose function in vivo remains poorly understood. To investigate the requirement of STI1-mediated regulation of the chaperone machinery in aging we combined analysis of a mouse line with a hypomorphic Stip1 allele, with a neuronal cell line lacking STI1 and in-depth analyses of chaperone genes in human datasets. Loss of STI1 function severely disturbed the Hsp70/Hsp90 machinery in vivo, and all client proteins tested and a subset of cochaperones presented decreased levels. Importantly, mice expressing a hypomorphic STI1 allele showed spontaneous age-dependent hippocampal neurodegeneration, with consequent spatial memory deficits. STI1 is a critical node for the chaperone network and it can contribute to age-dependent hippocampal neurodegeneration.

cell biology↗