Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biochemistry

Supervisor

Choy, Wing-Yiu

2nd Supervisor

Prado, Marco

Joint Supervisor

Abstract

Amyloid-beta oligomers (AbOs) induce neurological dysfunction in part through the cellular prion protein (PrPC) resulting in deregulation of Ca2+ homeostasis in Alzheimer’s disease (AD). Stress inducible phosphoprotein 1 (STIP1), a cochaperone of Hsp70 and Hsp90, protects neurons from AbO-induced cell death. As well, STIP1 interacts with the Ca2+ sensor S100A1, which is an important biomarker upregulated in AD and regulates STIP1 and other cochaperone association with Hsp70 and Hsp90. While the molecular details of STIP1-Hsp complexes are well studied, little information is available concerning alternate STIP1 binding partners. Here, we investigated the structural details of STIP1 binding to PrPC and S100A1.

We showed that residues located in a short region of PrP (90-110) mediate AbO and refined the main interaction to residues 91-100. We identified that STIP1 binds to PrP through multiple domains (DP1, TPR1 and TPR2A) and that the interactions with TPR1 and TPR2A effectively block AbO binding to PrPC and cell death. The DP1 domain interacted with the flexible N-terminal (residues 23-95), while TPR1 and TPR2A interacts with the C-terminal (residues 90-231) of PrP. NMR spectroscopy revealed that the TPR domains interact with PrP competitively through distinct regions, with the TPR2A binding site overlapping with Hsp90. Our data suggest PrP, STIP1 and Hsp90 may form a ternary complex, which may influence AbO toxicity in cells.

In contrast to PrP complex formation, S100A1 binding to STIP1 is Ca2+ dependent and mediated through the TPR (TPR1, TPR2A and TPR2B) domains of STIP1. Each TPR binds asymmetrically to a single S100A1 dimer resulting in a stoichiometry of three S100A1 dimers binding a single STIP1 molecule. S100A1 bound each TPR through a common interface spanning a-helix IV; however, with different binding affinities. Our findings provide novel structural insights regarding STIP1 complexes with PrPC and S100A1.

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