A novel copper(II) coordination at His186 in full-length murine prion protein

Copper drives prion protein phase separation and modulates aggregation

Prion diseases are characterized by prion protein (PrP) transmissible aggregation and neurodegeneration, which has been linked to oxidative stress. The physiological function of PrP seems related to sequestering of redox-active Cu2+, and Cu2+ dyshomeostasis is observed in prion disease brain. It is unclear whether Cu2+ contributes to PrP aggregation, recently shown to be mediated by PrP condensation. This study indicates that Cu2+ promotes PrP condensation in live cells at the cell surface and in vitro through copartitioning. Molecularly, Cu2+ inhibited PrP β-structure and hydrophobic residues exposure. Oxidation, induced by H2O2, triggered liquid-to-solid transition of PrP:Cu2+ condensates and promoted amyloid-like PrP aggregation. In cells, overexpression of PrPC initially protected against Cu2+ cytotoxicity but led to PrPC aggregation upon extended copper exposure. Our data suggest that PrP condensates function as a buffer for copper that prevents copper toxicity but can transition into PrP aggregation at prolonged oxidative stress.

Copper and Zinc Interactions with Cellular Prion Proteins Change Solubility of Full-Length Glycosylated Isoforms and Induce the Occurrence of Heterogeneous Phenotypes

Prion diseases are characterized biochemically by protein aggregation of infectious prion isoforms (PrP^Sc), which result from the conformational conversion of physiological prion proteins (PrP^C). PrP^C are variable post-translationally modified glycoproteins, which exist as full length and as aminoterminally truncated glycosylated proteins and which exhibit differential detergent solubility. This implicates the presence of heterogeneous phenotypes, which overlap as protein complexes at the same molecular masses. Although the biological function of PrP^C is still enigmatic, evidence reveals that PrP^C exhibits metal-binding properties, which result in structural changes and decreased solubility. In this study, we analyzed the yield of PrP^C metal binding affiliated with low solubility and changes in protein banding patterns. By implementing a high-speed centrifugation step, the interaction of zinc ions with PrP^C was shown to generate large quantities of proteins with low solubility, consisting mainly of full-length glycosylated PrP^C; whereas unglycosylated PrP^C remained in the supernatants as well as truncated glycosylated proteins which lack of octarepeat sequence necessary for metal binding. This effect was considerably lower when PrP^C interacted with copper ions; the presence of other metals tested exhibited no effect under these conditions. The binding of zinc and copper to PrP^C demonstrated differentially soluble protein yields within distinct PrP^C subtypes. PrP^C–Zn²⁺-interaction may provide a means to differentiate glycosylated and unglycosylated subtypes and offers detailed analysis of metal-bound and metal-free protein conversion assays.

FANTEN: a new web-based interface for the analysis of magnetic anisotropy-induced NMR data

Pseudocontact shifts (PCSs) and residual dipolar couplings (RDCs) arising from the presence of paramagnetic metal ions in proteins as well as RDCs due to partial orientation induced by external orienting media are nowadays routinely measured as a part of the NMR characterization of biologically relevant systems. PCSs and RDCs are becoming more and more popular as restraints (1) to determine and/or refine protein structures in solution, (2) to monitor the extent of conformational heterogeneity in systems composed of rigid domains which can reorient with respect to one another, and (3) to obtain structural information in protein-protein complexes. The use of both PCSs and RDCs proceeds through the determination of the anisotropy tensors which are at the origin of these NMR observables. A new user-friendly web tool, called FANTEN (Finding ANisotropy TENsors), has been developed for the determination of the anisotropy tensors related to PCSs and RDCs and has been made freely available through the WeNMR ( http://fanten-enmr.cerm.unifi.it:8080 ) gateway. The program has many new features not available in other existing programs, among which the possibility of a joint analysis of several sets of PCS and RDC data and the possibility to perform rigid body minimizations.

Effects of metal binding on solubility and resistance of physiological prions depend on tissues and glycotypes

Prion diseases entail the conversion of a normal host-encoded prion protein (PrP(C)) into an infectious isoform (PrP(Sc)). Various PrP(C) types differing in banding profiles and detergent solubility are present in different tissues, but only few PrP(Sc) types have been generated although PrP(C) acts as substrate. We hypothesize that distinct PrP(C) subtypes may be converted more efficiently to PrP(Sc) than others. One prerequisite for the analysis is the identification of the PrP(C) subtypes present in the protein complexes. Metal binding to PrP(C) is one of the most prominent features of the protein which induces increased proteolysis resistance and structural changes which might play an important role in the conversion process. Here we analyzed the metal-induced structural PrP(C) transformation of two different Triton X-100 soluble PrP(C) types derived from human platelets and brains by changes in protein solubility. We found that zinc and copper rendered approximately half of total PrP(C) and mainly un- and low-glycosylated PrP(C) to the Triton insoluble fraction. Our results indicate the presence of at least two distinct PrP(C) subtypes by metal interactions. The differentiation of high and low soluble metal bound PrP(C) offers precious information about PrP(C) protein composition and provides approaches for analyzing the transformation efficiency to PrP(Sc).

Copper alters aggregation behavior of prion protein and induces novel interactions between its N- and C-terminal regions

Copper is reported to promote and prevent aggregation of prion protein. Conformational and functional consequences of Cu(2+)-binding to prion protein (PrP) are not well understood largely because most of the Cu(2+)-binding studies have been performed on fragments and truncated variants of the prion protein. In this context, we set out to investigate the conformational consequences of Cu(2+)-binding to full-length prion protein (PrP) by isothermal calorimetry, NMR, and small angle x-ray scattering. In this study, we report altered aggregation behavior of full-length PrP upon binding to Cu(2+). At physiological temperature, Cu(2+) did not promote aggregation suggesting that Cu(2+) may not play a role in the aggregation of PrP at physiological temperature (37 °C). However, Cu(2+)-bound PrP aggregated at lower temperatures. This temperature-dependent process is reversible. Our results show two novel intra-protein interactions upon Cu(2+)-binding. The N-terminal region (residues 90-120 that contain the site His-96/His-111) becomes proximal to helix-1 (residues 144-147) and its nearby loop region (residues 139-143), which may be important in preventing amyloid fibril formation in the presence of Cu(2+). In addition, we observed another novel interaction between the N-terminal region comprising the octapeptide repeats (residues 60-91) and helix-2 (residues 174-185) of PrP. Small angle x-ray scattering studies of full-length PrP show significant compactness upon Cu(2+)-binding. Our results demonstrate novel long range inter-domain interactions of the N- and C-terminal regions of PrP upon Cu(2+)-binding, which might have physiological significance.