Domains of STIP1 responsible for regulating PrPC-dependent amyloid-β oligomer toxicity

Soluble oligomers of amyloid-beta peptide (A beta O) transmit neurotoxic signals through the cellular prion protein (PrPC) in Alzheimer's disease (AD). Secreted stress-inducible phosphoprotein 1 (STIP1), an Hsp70 and Hsp90 cochaperone, inhibits A beta O binding to PrPC and protects neurons from A beta O-induced cell death. Here, we investigated the molecular interactions between A beta O and STIP1 binding to PrPC and their effect on neuronal cell death. We showed that residues located in a short region of PrP (90-110) mediate A beta O binding and we narrowed the major interaction in this site to amino acids 91-100. In contrast, multiple binding sites on STIP1 (DP1, TPR1 and TPR2A) contribute to PrP binding. DP1 bound the N-terminal of PrP (residues 23-95), whereas TPR1 and TPR2A showed binding to the C-terminal of PrP (residues 90-231). Importantly, only TPR1 and TPR2A directly inhibit both A beta O binding to PrP and cell death. Furthermore, our structural studies reveal that TPR1 and TPR2A bind to PrP through distinct regions. The TPR2A interface was shown to be much more extensive and to partially overlap with the Hsp90 binding site. Our data show the possibility of a PrP, STIP1 and Hsp90 ternary complex, which may influence A beta O-mediated cell death.