Zinc significantly changes the aggregation pathway and the conformation of aggregates of human prion protein

Prion diseases are caused by the conformational change of cellular prion protein PrPC into pathological prion protein PrPSc. Here we study the effect of zinc on the aggregation and conformational change of human prion protein (PrP). As revealed by thioflavin T binding assays, Sarkosyl-soluble SDS-PAGE, and transmission electron microscopy, aggregation of wild-type PrP in the absence of Zn2+ undergoes four steps: amorphous aggregates, profibrils, mature fibrils, and fragmented fibrils. When the molar ratio of Zn2+ to PrP was 9:1, however, aggregation of wild-type PrP undergoes another pathway in which wild-type PrP forms oligomers quickly and then forms short-rod aggregates. Unlike wild-type PrP, the octarepeats deletion mutant PrP Delta octa forms typical mature fibrils either with or without zinc. As evidenced by isothermal titration calorimetry, Fourier transform infrared spectroscopy, and proteinase K digestion assays, Zn2+ strongly binds to wild-type PrP monomers with the first binding constant exceeding 10(7) M-1 under denaturing conditions, and changes the conformation of wild-type PrP aggregates remarkably, but weakly binds to PrP Delta octa with binding affinity around 10(4) M-1 and has no obvious effects on the conformation of PrP Delta octa aggregates. Our data demonstrate that zinc significantly changes the aggregation pathway and the conformation of wild-type PrP aggregates mainly via interaction with its octarepeat region. Our findings could explain how zinc modifies pathological PrP conformation associated with prion diseases. (C) 2015 Elsevier B.V. All rights reserved.