Structural Basis of Prion Inhibition by Phenothiazine Compounds

Abstract

Conformational transitions of the cellular form of the prion protein, PrP(C), into an infectious isoform, PrP(Sc), are considered to be central events in the progression of fatal neurodegenerative diseases known as transmissible spongiform encephalopathies. Tricyclic phenothiazine compounds exhibit antiprion activity; however, the underlying molecular mechanism of PrP(Sc) inhibition remains elusive. We report the molecular structures of two phenothiazine compounds, promazine and chlorpromazine bound to a binding pocket formed at the intersection of the structured and the unstructured domains of the mouse prion protein. Promazine binding induces structural rearrangement of the unstructured region proximal to β1, through the formation of a "hydrophobic anchor." We demonstrate that these molecules, promazine in particular, allosterically stabilize the misfolding initiator-motifs such as the C terminus of α2, the α2-α3 loop, as well as the polymorphic β2-α2 loop. Hence, the stabilization effects of the phenothiazine derivatives on initiator-motifs induce a PrP(C) isoform that potentially resists oligomerization.

Prion Protein—Antibody Complexes Characterized by Chromatography-Coupled Small-Angle X-Ray Scattering

“…PrP C consists of two domains, a disordered N-terminal domain (residues 23-124) and a globular C-terminal domain composed of three a-helices and two short antiparallel b-strands (residues 125-230). Structural studies using solution NMR spectroscopy and x-ray crystallography revealed the structure of the C-terminal domain (12)(13)(14)(15)(16)(17), but neither the structure of the flexible N-terminal domain of PrP C nor the structure of PrP Sc is known (18).…”

Insights from Therapeutic Studies for PrP Prion Disease

“…Recent advancements in structural chemistry and biology have made it possible to identify important structural features of PrP C , which has facilitated the investigation of interactions between PrP C and test compounds and has guided rational drug design (Kuwata 2013;Baral et al 2014). Accordingly, Venko et al (2014) computationally analyzed and summarized structure-activity relationships of small organic compounds using prion-infected cell-based assays.…”

Stability of Amyloid Oligomers

“…We will therefore focus in this review on stability studies of preformed amyloid aggregates in explicit water and show that such simulations can not only explain experimental observations but also guide future experiments Mousseau & Derreumaux, 2005). A striking example may be recent work by Baral et al (2014b), who by combining NMR and molecular dynamics simulations of the prion molecule bound to two anti-prion phenothiazines (i.e., promazine and chlorpromazine) explore how these two small molecules stabilize several PrP C motifs implicated in the transition to the neurotoxic PrP sc state. In this way, they can explain the ability of phenothiazine to inhibit prions and provide a road map for future efforts in computer-aided structure-guided search for anti-prion molecules with better activity and drug properties.…”

“…Deposits of amyloids are associated with a growing number of human illnesses (Chiti & Dobson, 2006;Eisenberg & Jucker, 2012); however, it appears that the most cell-toxic aggregates are not the fibrils themselves but the transient, pre-fibrillar oligomer species (Baglioni et al, 2006;Benilova, Karran, & De Strooper, 2012). Hydrophobic patches of the later can damage cells by disrupting cell membranes or through dislocation of other proteins in the cell (Baglioni et al, 2006;Baral et al, 2014a;Kayed & Lasagna-Reeves, 2013;Olzscha et al, 2011).…”

“…This would allow predictions of compounds which can interfere with these processes potentially leading to effective therapeutic agents (Baral et al, 2014a;Bemporad & Chiti, 2012;Merlini, Seldin, & Gertz, 2011). However, despite the highly ordered nature of amyloids, it is still a challenge to resolve their structure with sufficient resolution.…”