Prion protein binds copper within the physiological concentration range.

The prion protein is known to be a copper-binding protein, but affinity and stoichiometry data for the full-length protein at a physiological pH of 7 were lacking. Furthermore, it was unknown whether only the highly flexible N-terminal segment with its octarepeat region is involved in copper binding or whether the structured C-terminal domain is also involved. Therefore we systematically investigated the stoichiometry and affinity of copper binding to full-length prion protein PrP(23-231) and to different N- and C-terminal fragments using electrospray ionization mass spectrometry and fluorescence spectroscopy. Our data indicate that the unstructured N-terminal segment is the cooperative copper-binding domain of the prion protein. The prion protein binds up to five copper(II) ions with half-maximal binding at approximately 2 microm. This argues strongly for a direct role of the prion protein in copper metabolism, since it is almost saturated at about 5 microm, and the exchangeable copper pool concentration in blood is about 8 microm.

Adamantiades-Behçet's disease: interleukin-8 is increased in serum of patients with active oral and neurological manifestations and is secreted by small vessel endothelial cells.

The serum levels of several cytokines were determined in 94 patients with Adamantiades-Behçet's disease (ABD), aged 36.1+/-11.0 years, during the active stage (n = 75) and the inactive stage (n = 19) of the disease. A group of 75 healthy individuals matched for age and sex served as controls. Cytokine levels were determined using commercially available ELISA kits. Of the 75 patients with active disease and 19 with inactive disease, 38 (51%) and 4 (21%), respectively, and 23 healthy controls (31%) were found to have detectable levels of interleukin 8 (IL-8) in their serum (P < 0.05). Also, increased IL-8 serum levels were found in patients with active disease (median 12 pg/ml, P = 0.010) compared to patients with inactive disease (< or = 10 pg/ml) and to healthy controls (< or = 10 pg/ml). In particular, patients with oral aphthous ulcers (n = 51, 34 pg/ml) and neurological features (n = 4, 71 pg/ml) exhibited increased IL-8 levels. In contrast, there was no correlation between disease activity and the serum levels of IL-1alpha, IL-1beta, tumor necrosis factor alpha (TNF-alpha), soluble intercellular adhesion molecule-1 or basic fibroblast growth factor (bFGF). In a second set of experiments, the involvement of dermal microvascular endothelial cells in IL-8 secretion was investigated. Immortalized human dermal microvascular endothelial cells (HMEC-1 cells) were maintained for 4 h in vitro with serum from 18 ABD patients or with IL-1beta, a known stimulator of IL-8 synthesis, TNF-alpha or their combination at five- to tenfold higher concentrations than those found in the serum of ABD patients. Increased IL-8 secretion was found after incubation with ABD patients' serum (median 20 pg/ml), but IL-1beta, TNF-alpha and IL-1beta + TNF-alpha failed to induce IL-8 secretion by HMEC-1 cells (< or = 1-1.2 pg/ml) in biologically relevant concentrations. Our study showed increased IL-8 serum levels in ABD patients with active oral and neurological manifestations. Human microvascular endothelial cells may, at least partially, be responsible for the enhanced IL-8 secretion in the active stage of the disease.

Peptides and proteins in neurodegenerative disease: helix propensity of a polypeptide containing helix 1 of the mouse prion protein studied by NMR and CD spectroscopy.

Transmissible spongiform encephalopathies (TSE) or "prion diseases" have been related to the "protein-only hypothesis", which suggests that the "scrapie form (PrPSc)" of the prion protein (PrP) is the TSE infectious agent. The nmr structure of the ubiquitous benign cellular form of PrP (PrPC) consists of a globular domain of residues 126-231 with three alpha-helices and a short beta-sheet, and a flexible extended "tail" of residues 23-125. The peptide segment of helix 1 has been implicated in various stages of hypothetical pathways to prion pathology on the basis of the protein-only idea, including that it takes part in the conformation change that leads from PrPC to PrPSc. In this paper we describe solution nmr and circular dichroism studies of the synthetic hexadecapeptide mPrP(143-158), with the sequence H-NDWEDRYYRENMYRYP-NH2, where the bold letters represent the segment that forms helix 1 in murine PrPC. In both H2O and a 1:1 mixture of H2O and trifluoroethanol this polypeptide segment shows high helix propensity, which is a key issue in discussions on potential roles of this molecular region in conformational transitions of PrP.

Prion protein NMR structure and familial human spongiform encephalopathies.

The refined NMR structure of the mouse prion protein domain mPrP(121-231) and the recently reported NMR structure of the complete 208-residue polypeptide chain of mPrP are used to investigate the structural basis of inherited human transmissible spongiform encephalopathies. In the cellular form of mPrP no spatial clustering of mutation sites is observed that would indicate the existence of disease-specific subdomains. A hydrogen bond between residues 128 and 178 provides a structural basis for the observed highly specific influence of a polymorphism in position 129 in human PrP on the disease phenotype that segregates with the mutation Asp-178-Asn. Overall, the NMR structure implies that only part of the disease-related amino acid replacements lead to reduced stability of the cellular form of PrP, indicating that subtle structural differences in the mutant proteins may affect intermolecular signaling in a variety of different ways.

Prion protein expression in different species: analysis with a panel of new mAbs.

By immunizing prion knockout mice (Prnp-/-) with recombinant murine prion protein (PrPc), we obtained a panel of mAbs specific for murine PrPc. These mAbs can be applied to immunoblotting, cell surface immunofluorescent staining, and immunohistochemistry at light and electron microscopy. These mAbs recognize both the normal (PrPc) and protease-resistant (PrPres) isoforms of PrP. Some mAbs are species restricted, while others react with PrP from a broad range of mammals including mice, humans, monkeys, cows, sheep, squirrels, and hamsters. Moreover, some of the mAbs selectively recognize different PrP glycoforms as well as the metabolic fragments of PrPc. These newly generated PrPc antibodies will help to explore the biology of PrPc and to establish the diagnosis of prion diseases in both humans and animals.

A scrapie-like unfolding intermediate of the prion protein domain PrP(121-231) induced by acidic pH.

The infectious agent of transmissible spongiform encephalopathies is believed to consist of an oligomeric isoform, PrPSc, of the monomeric cellular prion protein, PrPC. The conversion of PrPC to PrPSc is characterized by a decrease in alpha-helical structure, an increase in beta-sheet content, and the formation of PrPSc amyloid. Whereas the N-terminal part of PrPC comprising residues 23-120 is flexibly disordered, its C-terminal part, PrP(121-231), forms a globular domain with three alpha-helices and a small beta-sheet. Because the segment of residues 90-231 is protease-resistant in PrPSc, it is most likely structured in the PrPSc form. The conformational change of the segment containing residues 90-120 thus constitutes the minimal structural difference between PrPC and a PrPSc monomer. To test whether PrP(121-231) is also capable to undergo conformational transitions, we analyzed its urea-dependent unfolding transitions at neutral and acidic pH. We identified an equilibrium unfolding intermediate of PrP(121-231) that is exclusively populated at acidic pH and shows spectral characteristics of a beta-sheet protein. The intermediate is in rapid equilibrium with native PrP(121-231), significantly populated in the absence of urea at pH 4.0, and may have important implications for the presumed formation of PrPSc during endocytosis.

Prion protein structural features indicate possible relations to signal peptidases.

Transmissible spongiform encephalopathies (TSEs) in mammalian species are believed to be caused by an oligomeric isoform, PrP(Sc), of the cellular prion protein, PrP(C). One of the key questions in TSE research is how the observed accumulation of PrP(Sc), or possibly the concomitant depletion of PrP(C) can cause fatal brain damage. Elucidation of the so far unknown function of PrP(C) is therefore of crucial importance. PrP(C) is a membrane-anchored cell surface protein that possesses a so far unique three-dimensional structure. While the N-terminal segment 23-120 of PrP(C) is flexibly disordered, its C-terminal residues 121-231 form a globular domain with three alpha-helices and a two-stranded beta-sheet. Here we report the observation of structural similarities between the domain of PrP(121-231) and the soluble domains of membrane-anchored signal peptidases. At the level of the primary structure we find 23% identity and 41% similarity between residues 121-217 of the C-terminal domain of murine PrP and a catalytic domain of the rat signal peptidase. The invariant PrP residues Tyr-128 and His-177 align with the two presumed active-site residues of signal peptidases and are in close spatial proximity in the three-dimensional structure of PrP(121-231).

The human sebocyte culture model provides new insights into development and management of seborrhoea and acne.

Seborrhoea and acne are exclusively human diseases and sebaceous gland differentiation is species specific. Therefore, fundamental research on human sebaceous cell function and control requires human in vitro models. The human sebocyte culture model, introduced in 1989, has been used in several studies to elucidate sebaceous gland activity and its regulation at the cellular level. Cultured human sebocytes have been shown to preserve important sebocytic characteristics, although they undergo an incomplete terminal differentiation in vitro. In vitro synthesis of free fatty acids without bacterial involvement and marked interleukin 1 alpha expression at the mRNA and protein levels with no further induction by lipopolysaccharides lead to the assumption that human sebocytes may initiate acne lesions by an intrinsic mechanism. Androgens affected sebocyte activity in vitro in a manner dependent on the localization of the sebaceous glands. In vitro stimulation of sebocyte proliferation by androgens could be completely abolished by spironolactone. Cultured sebocytes strongly expressed type 1 5 alpha-reductase and metabolized testosterone to androstenedione, 5 alpha-androstanedione, 5 alpha-dihydrotestosterone, androsterone and 5 alpha-androstanediol, whereas the levels of 5 alpha-reductase activity were probably not feedback regulated. 4,7 beta-Dimethyl-4-aza-5 alpha-cholestan-3-one, a type 1 5 alpha-reductase inhibitor, induced an early, marked down-regulation of 5 alpha-reductase activity in human sebocytes in vitro, while hydrofinasteride, a type 2 inhibitor, required 10(3)-fold higher concentrations to induce similar effects. Stimulation of sebocyte proliferation by insulin, thyroid-stimulating hormone and hydrocortisone indicates that the hormonal control of the sebaceous gland could be a complex mechanism. Retinoids inhibited sebocyte proliferation in a dose-dependent manner and down-regulated lipid synthesis and sebocyte differentiation in vitro. Isotretinoin was the most potent compound. On the other hand, vitamin A was found essential for sebocyte activity and differentiation in vitro and could be partially substituted by synthetic retinoids. The inhibitory effect of isotretinoin on sebocyte proliferation was barely affected by the presence of vitamin A. The low persistent isotretinoin levels or, more likely, the considerably elevated tretinoin concentrations detected in human sebocytes after treatment with isotretinoin in vitro may be responsible for the inhibitory effect of this compound on sebocyte activity.

Prion (PrPSc)-specific epitope defined by a monoclonal antibody.

Prions are infectious particles causing transmissible spongiform encephalopathies (TSEs). They consist, at least in part, of an isoform (PrPSc) of the ubiquitous cellular prion protein (PrPC). Conformational differences between PrPC and PrPSc are evident from increased beta-sheet content and protease resistance in PrPSc. Here we describe a monoclonal antibody, 15B3, that can discriminate between the normal and disease-specific forms of PrP. Such an antibody has been long sought as it should be invaluable for characterizing the infectious particle as well as for diagnosis of TSEs such as bovine spongiform encephalopathy (BSE) or Creutzfeldt-Jakob disease (CJD) in humans. 15B3 specifically precipitates bovine, murine or human PrPSc, but not PrPC, suggesting that it recognizes an epitope common to prions from different species. Using immobilized synthetic peptides, we mapped three polypeptide segments in PrP as the 15B3 epitope. In the NMR structure of recombinant mouse PrP, segments 2 and 3 of the 15B3 epitope are near neighbours in space, and segment 1 is located in a different part of the molecule. We discuss models for the PrPSc-specific epitope that ensure close spatial proximity of all three 15B3 segments, either by intermolecular contacts in oligomeric forms of the prion protein or by intramolecular rearrangement.

Recombinant full-length murine prion protein, mPrP(23-231): purification and spectroscopic characterization.

The cellular prion protein of the mouse, mPrP(C), consists of 208 amino acids (residues 23-231). It contains a carboxy-terminal domain, mPrP(121-231), which represents an autonomous folding unit with three alpha-helices and a two-stranded antiparallel beta-sheet. We expressed the complete amino acid sequence of the prion protein, mPrP(23-231), in the cytoplasm of Escherichia coli. mPrP(23-231) was solubilized from inclusion bodies by 8 M urea, oxidatively refolded and purified to homogeneity by conventional chromatographic techniques. Comparison of near-UV circular dichroism, fluorescence and one-dimensional 1H-NMR spectra of mPrP(23-231) and mPrP(121-231) shows that the amino-terminal segment 23-120, which includes the five characteristic octapeptide repeats, does not contribute measurably to the manifestation of three-dimensional structure as detected by these techniques, indicating that the residues 121-231 might be the only polypeptide segment of PrP(C) with a defined three-dimensional structure.

NMR characterization of the full-length recombinant murine prion protein, mPrP(23-231).

The recombinant murine prion protein, mPrP(23-231), was expressed in E. coli with uniform 15N-labeling. NMR experiments showed that the previously determined globular three-dimensional structure of the C-terminal domain mPrP(121-231) is preserved in the intact protein, and that the N-terminal polypeptide segment 23-120 is flexibly disordered. This structural information is based on nearly complete sequence-specific assignments for the backbone amide nitrogens, amide protons and alpha-protols of the polypeptide segment of residues 121-231 in mPrP(23-231). Coincidence of corresponding sequential and medium-range nuclear Overhauser effects (NOE) showed that the helical secondary structures previously identified in mPrP(121-231) are also present in mPrP(23-231), and near-identity of corresponding amide nitrogen and amide proton chemical shifts indicates that the three-dimensional fold of mPrP(121-231) is also preserved in the intact protein. The linewidths in heteronuclear 1H-15N correlation spectra and 15N[1H]-NOEs showed that the well structured residues 126-230 have correlation times of several nanoseconds, as is typical for small globular proteins, whereas correlation times shorter than 1 nanosecond were observed for all residues of mPrP(23-231) outside of this domain.

Prion protein NMR structure and species barrier for prion diseases.

The structural basis of species specificity of transmissible spongiform encephalopathies, such as bovine spongiform encephalopathy or "mad cow disease" and Creutzfeldt-Jakob disease in humans, has been investigated using the refined NMR structure of the C-terminal domain of the mouse prion protein with residues 121-231. A database search for mammalian prion proteins yielded 23 different sequences for the fragment 124-226, which display a high degree of sequence identity and show relevant amino acid substitutions in only 18 of the 103 positions. Except for a unique isolated negative surface charge in the bovine protein, the amino acid differences are clustered in three distinct regions of the three-dimensional structure of the cellular form of the prion protein. Two of these regions represent potential species-dependent surface recognition sites for protein-protein interactions, which have independently been implicated from in vitro and in vivo studies of prion protein transformation. The third region consists of a cluster of interior hydrophobic side chains that may affect prion protein transformation at later stages, after initial conformational changes in the cellular protein.

Autonomous and reversible folding of a soluble amino-terminally truncated segment of the mouse prion protein.

Prion diseases are assumed to be caused by the infectious isoform, PrPsc, of a single cellular surface protein, PrPc. PrPsc is an insoluble form of PrPc and is believed to possess a different three-dimensional fold. It may propagate by causing PrPc to adopt its own infectious conformation by an unknown mechanism. Studies on folding and thermodynamic stability of prion proteins are essential for understanding the processes underlying the conversion from PrPc to PrPsc, but have so far been hampered by the low solubility of prion proteins in the absence of detergents. Here, we show that the amino-terminally truncated segment of mouse PrP comprising residues 121 to 231 is an autonomous folding unit. It consists predominantly of alpha-helical secondary structure and is soluble at high concentrations up to 1 mM in distilled water. PrP(121-231) undergoes a cooperative and completely reversible unfolding/refolding transition in the presence of guanidinium chloride with a free energy of folding of -22 kJ/mol at pH 7. The intrinsic stability of segment 121-231 is not in accordance with present models of the structure of PrPc and PrPsc PrP(121-231) may represent the only part of PrPc with defined three-dimensional structure.

NMR structure of the mouse prion protein domain PrP(121-231).

The 'protein only' hypothesis states that a modified form of normal prion protein triggers infectious neurodegenerative diseases, such as bovine spongiform encephalopathy (BSE), or Creutzfeldt-Jakob disease (CJD) in humans. Prion proteins are thought to exist in two different conformations: the 'benign' PrPcform, and the infectious 'scrapie form', PrPsc. Knowledge of the three-dimensional structure of PrPc is essential for understanding the transition to PrPsc. The nuclear magnetic resonance (NMR) structure of the autonomously folding PrP domain comprising residues 121-231 (ref. 6) contains a two-stranded antiparallel beta-sheet and three alpha-helices. This domain contains most of the point-mutation sites that have been linked, in human PrP, to the occurrence of familial prion diseases. The NMR structure shows that these mutations occur within, or directly adjacent to, regular secondary structures. The presence of a beta-sheet in PrP(121-231) is in contrast with model predictions of an all-helical structure of PrPc (ref. 8), and may be important for the initiation of the transition from PrPc to PrPsc.