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The most common form of prion disease in humans is sCJD (sporadic Creutzfeldt-Jakob disease). The naturally occurring E219K polymorphism in the HuPrP (human prion protein) is considered to protect against sCJD. To gain insight into the structural basis of its protective influence we have determined the NMR structure of recombinant HuPrP (residues 90-231) carrying the E219K polymorphism. The structure of the HuPrP(E219K) protein consists of a disordered N-terminal tail (residues 90-124) and a well-structured C-terminal segment (residues 125-231) containing three α-helices and two short antiparallel β-strands. Comparison of NMR structures of the wild-type and HuPrPs with pathological mutations under identical experimental conditions revealed that, although the global architecture of the protein remains intact, replacement of Glu²¹⁹ with a lysine residue introduces significant local structural changes. The structural findings of the present study suggest that the protective influence of the E219K polymorphism is due to the alteration of surface charge distribution, in addition to subtle structural rearrangements localized within the epitopes critical for prion conversion.

The nucleobase adenine plays a pivotal role in the chemistry of life, but is also becoming increasingly interesting as a building block in the synthesis of functional solid materials.Although commercially available as a solid, adenine's solid-state chemistry has so far been neglected. In this comprehensive study it is shown that adenine is most often marketed as a mixture of two polymorphs, one previously known, and a new polymorph.Both polymorphs exhibit layered structures with different hydrogen-bonding patterns within layers. The crystal structure of the new polymorph was elucidated using synchrotron powder X-ray diffraction. Polymorph occurrence conditions, interconversion and the difference in their thermodynamic stability were established theoretically and experimentally revealing the polymorph with Z = 2 (known) as stable relative to the polymorph with Z = 1 (new). The adenine layers in both polymorphs are connected by weak interaction likely resulting in stacking faults which are manifested in anisotropic line broadening of their powder diffraction patterns. Analysis of a few commercial samples of adenine revealed them all to be a polymorph mixture, which could be inconvenient in experiments where properties of the solid material could be relevant.

A major focus in prion structural biology studies is unraveling the molecular mechanism leading to the structural conversion of PrP(C) to its pathological form, PrP(Sc). In our recent studies, we attempted to understand the early events of the conformational changes leading to PrP(Sc) using as investigative tools point mutations clustered in the open reading frame of the human PrP gene and linked to genetic forms of human prion diseases. In the work presented here, we investigate the effect of pH on the nuclear magnetic resonance (NMR) structure of recombinant human PrP (HuPrP) carrying the pathological V210I mutation responsible for familial Creutzfeldt-Jakob disease. The NMR structure of HuPrP(V210I) determined at pH 7.2 shows the same overall fold as the previously determined structure of HuPrP(V210I) at pH 5.5. It consists of a disordered N-terminal tail (residues 90-124) and a globular C-terminal domain (residues 125-231) comprising three α-helices and a short antiparallel β-sheet. Detailed comparison of three-dimensional structures of HuPrP(V210I) at pH 7.2 and 5.5 revealed significant local structural differences, with the most prominent pH-related structural variations clustered in the α(2)-α(3) interhelical region, at the interface of the β(1)-α(1) loop, in helices α(1) and α(3), and in the β(2)-α(2) loop region. The detailed analysis of interactions among secondary structure elements suggests a higher degree of structural ordering of HuPrP(V210I) under neutral-pH conditions, thus implying that spontaneous misfolding of PrP(C) may occur under acidic-pH conditions in endosomal compartments.

Abstract:The post-translational conversion of the ubiquitously expressed cellular form of the prion protein, PrP C , into its misfolded and pathogenic isoform, known as prion or PrP Sc , plays a key role in prion diseases. These maladies are denoted transmissible spongiform encephalopathies (TSEs) and affect both humans and animals. A prerequisite for understanding TSEs is unraveling the molecular mechanism leading to the conversion process whereby most α-helical motifs are replaced by β-sheet secondary structures. Importantly, most point mutations linked to inherited prion diseases are clustered in the C-terminal domain region of PrP C and cause spontaneous conversion to PrP Sc . Structural studies with PrP variants promise new clues regarding the proposed conversion mechanism and may help identify "hot spots" in PrP C involved in the pathogenic conversion. These investigations may also shed light on the early structural rearrangements occurring in some PrP C epitopes thought to be involved in modulating prion susceptibility. Here we present a detailed overview of our solution-state NMR studies on human prion protein carrying different pathological point mutations and the implications that such findings may have for the future of prion research.

The cellular form of the prion protein (PrP C ) is a highly conserved glycoprotein mostly expressed in the central and peripheral nervous systems by different cell types in mammals. A misfolded, pathogenic isoform, denoted as prion, is related to a class of neurodegenerative diseases known as transmissible spongiform encephalopathy. PrP C function has not been unequivocally clarified, and it is rather defined as a pleiotropic protein likely acting as a dynamic cell surface scaffolding protein for the assembly of different signaling modules. Among the variety of PrP C protein interactors, the neuronal cell adhesion molecule (NCAM) has been studied in vivo, but the structural basis of this functional interaction is still a matter of debate. Here we focused on the structural determinants responsible for human PrP C (HuPrP) and NCAM interaction using stimulated emission depletion (STED) nanoscopy, SPR, and NMR spectroscopy approaches. PrP C co-localizes with NCAM in mouse hippocampal neurons, and this interaction is mainly mediated by the intrinsically disordered PrP C N-terminal tail, which binds with high affinity to the NCAM fibronectin type-3 domain. NMR structural investigations revealed surface-interacting epitopes governing the interaction between HuPrP N terminus and the second module of the NCAM fibronectin type-3 domain. Our data provided molecular details about the interaction between HuPrP and the NCAM fibronectin domain, and revealed a new role of PrP C N terminus as a dynamic and functional element responsible for protein-protein interaction.A misfolded form of the host-encoded cellular prion protein (PrP C ) 3 is the causative agent for a class of human and animal neurodegenerative diseases denoted as transmissible spongiform encephalopathies. PrP C is a sialoglycoprotein, tethered to the outer leaflet of the plasma membrane by a glycosylphosphatidylinositol (GPI) anchor. Soluble, natively ␣-helix-folded monomers of PrP C may adopt an aggregated protease-resistant conformation known as PrP Sc (1). The mature human PrP C (HuPrP) is composed of 209 residues including a largely unstructured N-terminal part and a globular ␣-helix-rich C-terminal domain (2). Conversely, PrP Sc is ␤-sheet-enriched, partially protease-resistant, insoluble, and multimeric (3). The insoluble nature of PrP Sc and its propensity to aggregate have hampered the use of high-resolution techniques, and therefore different PrP Sc models currently exist (4). Despite the fact that PrP C is highly conserved among different species, its physiological function has not been fully clarified. Defining PrP C function remains one of the main challenges in prion biology, and it is also an absolute requirement for understanding prion diseases. It is now being accepted that PrP C is a pivotal molecule with diverse roles in brain development and in neural plasticity in the adult (5-8). Proposed PrP C functions range from neuronal growth and differentiation (9), synaptic plasticity (10, 11), cell signaling (12, * This work was supported by the EC th...

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Among the other porous materials, porous organic polymers have already proved as a valuable alternative for the selective adsorption of CO2 over N2. In a rational design of new porous...