Octapeptide Repeat Research Articles

Histidines in the Octapeptide Repeat of PrPC React with PrPSc at an Acidic pH

Cellular PrP is actively cycled between the cell surface and the endosomal pathway. The exact site and mechanism of conversion from PrP(C) to PrP(Sc) remain unknown. We have previously used recombinant antibodies containing grafts of PrP sequence to identify three regions of PrP(C) (aa23-27, 98-110, and 136-158) that react with PrP(Sc) at neutral pH. To determine if any regions of PrP(C) react with PrP(Sc) at an acidic pH similar to that of an endosomal compartment, we tested our panel of grafted antibodies for the ability to precipitate PrP(Sc) in a range of pH conditions. At pH near or lower than 6, PrP-grafted antibodies representing the octapeptide repeat react strongly with PrP(Sc) but not PrP(C). Modified grafts in which the histidines of the octarepeat were replaced with alanines did not react with PrP(Sc). PrP(Sc) precipitated by the octapeptide at pH 5.7 was able to seed conversion of normal PrP to PrP(Sc) in vitro. However, modified PrP containing histidine to alanine substitutions within the octapeptide repeats was still converted to PrP(Sc) in N2a cells. These results suggest that once PrP has entered the endosomal pathway, the acidic environment facilitates the binding of PrP(Sc) to the octarepeat of PrP(C) by the change in charge of the histidines within the octarepeat.

Heparin Binding by Murine Recombinant Prion Protein Leads to Transient Aggregation and Formation of RNA-Resistant Species

The conversion of cellular prion protein (PrP(C)) into the pathological conformer PrP(Sc) requires contact between both isoforms and probably also requires a cellular factor, such as a nucleic acid or a glycosaminoglycan (GAG). Little is known about the structural features implicit in the GAG-PrP interaction. In the present work, light scattering, fluorescence, circular dichroism, and nuclear magnetic resonance (NMR) spectroscopy were used to describe the chemical and physical properties of the murine recombinant PrP 23-231 interaction with low molecular weight heparin (LMWHep) at pH 7.4 and 5.5. LMWHep interacts with rPrP 23-231, thereby inducing transient aggregation. The interaction between murine rPrP and heparin at pH 5.5 had a stoichiometry of 2:1 (LMWHep:rPrP 23-231), in contrast to a 1:1 binding ratio at pH 7.4. At binding equilibrium, NMR spectra showed that rPrP complexed with LMWHep had the same general fold as that of the free protein, even though the binding can be indicated by significant changes in few residues of the C-terminal domain, especially at pH 5.5. Notably, the soluble LMWHep:rPrP complex prevented RNA-induced aggregation. We also investigated the interaction between LMWHep and the deletion mutants rPrP Δ51-90 and Δ32-121. Heparin did not bind these constructs at pH 7.4 but was able to interact at pH 5.5, indicating that this glycosaminoglycan binds the octapeptide repeat region at pH 7.4 but can also bind other regions of the protein at pH 5.5. The interaction at pH 5.5 was dependent on histidine residues of the murine rPrP 23-231. Depending on the cellular milieu, the PrP may expose different regions that can bind GAG. These results shed light on the role of GAGs in PrP conversion. The transient aggregation of PrP may explain why some GAGs have been reported to induce the conversion into the misfolded, scrapie conformation, whereas others are thought to protect against conversion. The acquired resistance of the complex against RNA-induced aggregation explains some of the unique properties of the PrP interaction with GAGs.

Signal transduction in neurons: effects of cellular prion protein on fyn kinase and ERK1/2 kinase

BackgroundIt has been reported that cellular prion protein (PrPc) co-localizes with caveolin-1 and participates to signal transduction events by recruiting Fyn kinase. As PrPc is a secreted protein anchored to the outer surface membrane through a glycosylphosphatidylinositol (GPI) anchor (secPrP) and caveolin-1 is located in the inner leaflet of plasma membrane, there is a problem of how the two proteins can physically interact each other and transduce signals.ResultsBy using the GST-fusion proteins system we observed that PrPc strongly interacts with caveolin-1 scaffolding domain and with a caveolin-1 hydrophilic C-terminal region, but not with the caveolin-1 N-terminal region. In vitro binding experiments were also performed to define the site(s) of PrPc interacting with cav-1. The results are consistent with a participation of PrPc octapeptide repeats motif in the binding to caveolin-1 scaffolding domain. The caveolar localization of PrPc was ascertained by co-immunoprecipitation, by co-localization after flotation in density gradients and by confocal microscopy analysis of PrPc and caveolin-1 distributions in a neuronal cell line (GN11) expressing caveolin-1 at high levels.ConclusionsWe observed that, after antibody-mediated cross-linking or copper treatment, PrPc was internalized probably into caveolae. We propose that following translocation from rafts to caveolae or caveolae-like domains, secPrP could interact with caveolin-1 and induce signal transduction events.

Diversity of prion diseases: (no) strains attached?

Prion diseases are neurodegenerative disorders with a remarkable variability in their clinical presentation, histopathological features and molecular pathology. Prion diseases in humans include (1) sporadic prion disease (sporadic Creutzfeldt-Jakob disease, sCJD), (2) inherited forms of prion diseases (also termed genetic or familial prion disease) such as the Gerstmann–Straussler–Scheinker syndrome (GSS), fatal familial insomnia (FFI) or octapeptide repeat inserts (OPRI) and (3) acquired forms, such as iatrogenic CJD (iCJD), Kuru, and variant CJD (vCJD) [transmission of bovine spongiform encephalopathy (BSE) to humans]. The protein-only hypothesis postulates that the infectious agent, termed ‘‘prion’’ [9], is composed predominantly (if not entirely) of aggregates of misfolded, host-encoded, cellular prion protein (PrP), commonly designated PrP [15]. The partially protease resistant, misfolded (‘‘scrapie’’-) isoform PrP is formed from normal (‘‘cellular’’) host prion protein (PrP) through conformational conversion. The common neuropathological features of prion diseases are a predominantly extracellular accumulation of PrP in the central nervous system. Prion protein deposits can vary considerably in their pattern, distribution and intensity [16, 18]. More than 80% of human prion diseases manifest as sporadic CJD with an incidence of 1–2 cases per million population per year across the world, and are equally frequent in men and women. Ca. 15% of human prion diseases are associated with autosomal dominant pathogenic mutations in the PRNP gene. To date, 37 pathogenic mutations and 19 non-coding polymorphisms have been described [1]. In contrast, acquired human prion diseases are rare: transmission of sCJD prions occurred through treatment with pituitary hormones pooled from human cadavers, transplantation of dura mater or cornea, the use of contaminated EEG electrodes [3], and by cannibalism among the Fore linguistic group in Papua New Guinea [2, 7]. Instead, variant CJD occurred mainly in the UK and in other countries due to human exposure to BSE prions [5], and more recently in a few cases by transmission of vCJD contaminated blood products. A striking phenomenon of prion diseases is the existence of so-called strains. In human sporadic prion disease at least four, possibly a dozen molecular strain types (including subtypes) can be identified. The strain type is related to the clinical phenotype, the histopathological appearance, and the polymorphism on codon 129 of the human prion (PRNP) gene. The molecular strain type is classified by both, fragment size and the ratio of three principal PrP bands seen after limited protease digestion. Importantly, inherited forms show a wide variability of patterns on immunoblots and often do not fit into the scheme that was originally established for sCJD, iCJD and vCJD. The cluster ‘‘prion diseases’’ in this issue of Acta Neuropathologica contains both, review articles and original papers, featuring the relationship of prions with tau, inherited prion diseases, the biology of strains, processing of PrP in the brain and the principle of protein misfolding cyclical amplification (PCMA). Prion diseases share a number of features with other amyloid forming diseases of the CNS, most prominently Alzheimer’s disease, but also other rare conditions such as Familial British Dementia (Worster Drought syndrome). S. Brandner (&) Department of Neurodegenerative Disease and Division of Neuropathology, UCL Institute of Neurology, London WC1N 3BG, UK e-mail: s.brandner@ion.ucl.ac.uk; sebastian.brandner@prion.ucl.ac.uk

Genetic Creutzfeldt–Jakob disease and fatal familial insomnia: insights into phenotypic variability and disease pathogenesis

Human prion diseases are a group of rare neurodegenerative disorders characterized by the conversion of the constitutively expressed prion protein, PrP(C), into an abnormally aggregated isoform, called PrP(Sc). While most people who develop a prion disease have no identifiable cause and a few acquire the disease through an identified source of infection, about 10-15% of patients are affected by a genetic form and carry either a point mutation or an insertion of octapeptide repeats in the prion protein gene. Prion diseases show the highest extent of phenotypic heterogeneity among neurodegenerative disorders and comprise three major disease entities with variable though overlapping phenotypic features: Creutzfeldt-Jakob disease (CJD), fatal insomnia and the Gerstmann-Sträussler-Scheinker syndrome. Both CJD and fatal insomnia are fully transmissible diseases, a feature that led to the isolation and characterization of different strains of the agent or prion showing distinctive clinical and neuropathological features after transmission to syngenic animals. Here, we review the current knowledge of the effects of the pathogenic mutations linked to genetic CJD and fatal familial insomnia on the prion protein metabolism and physicochemical properties, the disease phenotype and the strain characteristics. The data derived from studies in vitro and from those using cell and animal models are compared with those obtained from the analyses of the naturally occurring disease. The extent of phenotypic variation in genetic prion disease is analyzed in comparison to that of the sporadic disease, which has recently been the topic of a systematic and detailed characterization.

POD03 Distinct neuropsychological profiles correspond to distribution of cortical thinning in inherited prion disease caused by insertional mutation

There are at least 30 different mutations in the prion gene that cause clinical disease. Two of the most frequent in the UK are six octapeptide repeat insertion (6-OPRI) and...

Anionic Phospholipid Interactions of the Prion Protein N Terminus Are Minimally Perturbing and Not Driven Solely by the Octapeptide Repeat Domain

Although the N terminus of the prion protein (PrP(C)) has been shown to directly associate with lipid membranes, the precise determinants, biophysical basis, and functional implications of such binding, particularly in relation to endogenously occurring fragments, are unresolved. To better understand these issues, we studied a range of synthetic peptides: specifically those equating to the N1 (residues 23-110) and N2 (23-89) fragments derived from constitutive processing of PrP(C) and including those representing arbitrarily defined component domains of the N terminus of mouse prion protein. Utilizing more physiologically relevant large unilamellar vesicles, fluorescence studies at synaptosomal pH (7.4) showed absent binding of all peptides to lipids containing the zwitterionic headgroup phosphatidylcholine and mixtures containing the anionic headgroups phosphatidylglycerol or phosphatidylserine. At pH 5, typical of early endosomes, quartz crystal microbalance with dissipation showed the highest affinity binding occurred with N1 and N2, selective for anionic lipid species. Of particular note, the absence of binding by individual peptides representing component domains underscored the importance of the combination of the octapeptide repeat and the N-terminal polybasic regions for effective membrane interaction. In addition, using quartz crystal microbalance with dissipation and solid-state NMR, we characterized for the first time that both N1 and N2 deeply insert into the lipid bilayer with minimal disruption. Potential functional implications related to cellular stress responses are discussed.

Allele Distributions and Frequencies of the Six Prion Protein Gene (PRNP) Polymorphisms in Asian Native Cattle, Japanese Breeds, and Mythun (Bos frontalis)

Six polymorphic sites of the bovine prion protein gene (PRNP) were genotyped in 569 animals of Asian native cattle, Japanese breeds, purebred mythun (Bos frontalis), and mythun x cattle composite animals. At the 23-bp indel site, a deletion (23-) allele was a major allele in all populations except mythun. At the 12-bp indel site, an insertion (12+) allele was a major allele in all populations. The 14-bp indel site was polymorphic in all Asian native cattle. In the octapeptide repeat region, a six-repeat allele was a major allele in all populations, and 5/5 and 4/6 genotypes were detected in Japanese Black and Mongolian cattle and in mythun, respectively. Two nonsynonymous single nucleotide polymorphisms (SNPs) (K3T and S154N) were detected in Asian native cattle and mythun. Haplotype analysis using the genotypes of the six sites estimated 33 different haplotypes. The haplotype 23- 12- K 6 S 14+ was found in all populations.

Characterization of two isoforms of human SPRR3 from saliva of preterm human newborn and autoptic fetal oral mucosa, parotid and submandibular gland samples

RP-HPLC–ESI-MS profile of saliva samples from human preterm newborn showed a protein peak in the elution range 26.6–27.6 min. Deconvolution of ESI-MS spectra revealed the presence of two proteins with average molecular mass (Mav) values of 17,239 ± 3 Da and 18,065 ± 3 Da in 9 samples, with Mav value of 17,239 ± 3 Da in 4 samples and Mav value of 18,065 ± 3 Da in 2 samples. MALDI-TOF-MS analysis of tryptic digest allowed identifying the proteins as two isoforms of small proline-rich protein 3 and cDNA amplification of RNA extracts from oral mucosa, parotid and submandibular gland samples, obtained at fetal autopsy, provided two nucleotide sequences in agreement with those reported in the literature. The two proteins differ for an octapeptide repeat (GCTKVPEP) and the substitution Leu → Val, at position 148 and 140 of the mature form of the 18,065 and 17,239 Da protein, respectively. During maturation the two proteins undergo two post-translational modifications, corresponding to N-terminal acetylation and removal of the initiator methionine. cDNA amplification did not allow to clarify if the proteins found in saliva originated from cellular shedding of the epithelium and/or secretion.

PRNP allelic series from 19 years of prion protein gene sequencing at the MRC Prion Unit

Mutation of the human prion protein gene (PRNP) open reading frame (ORF) accounts for almost all reported familial concurrence of prion disease. The more common mutations globally: octapeptide repeat insertions, P102L, D178N, E200K, and V210I have occurred in large multigenerational pedigrees and display autosomal dominant inheritance, however, many rare genetic changes have been reported that are of uncertain pathogenicity. Based on 19 years of PRNP sequencing at the MRC Prion Unit, London, and analysis of 3664 samples from patients referred with suspected prion disease and healthy populations, we present novel allele combinations, healthy control population data, results of screening the PRNP ORF in DNA from the entire referral series and the CEPH human genome diversity cell line panel. Of the 10 alleles detected in patients for which detailed cases histories are presented, 4 are unreported (G54S, D167N, V209M, Q212PP), two changes are thought to be pathogenic but have not been described in our regions (P105L from the UK, G114V from India and Turkey), and the remainder reported in healthy control populations or in trans to known pathogenic mutations suggesting non- or low pathogenicity (G54S, 1-OPRI, G142S, N171S, V209M, E219K). New genotype-phenotype correlations and population frequencies presented will help the diagnosis and genetic counselling of those with suspected inherited prion disease.

Polymorphisms of the Prion Protein Gene (PRNP) in a Serbian Population

ABSTRACTPrion diseases are a group of etiologically heterogenous neurodegenerative disorders. We have analyzed the coding region of PRNP gene in 121 healthy citizens of Serbia to determine whether the frequencies of M129V, E219K, and octapeptide repeat number polymorphism. For Serbian population, polymorphism of PRNP gene at codon 129 does not differ from healthy European populations. Also codon 219 is monomorphic for the Glu allele both in Serbian population and other European populations. On the contrary, in Serbian population we did not detect any deletions or insertions in octapeptide repeat region, whereas deletions were detected in other European populations.

A novel seven-octapeptide repeat insertion in the prion protein gene (PRNP) in a Dutch pedigree with Gerstmann–Sträussler–Scheinker disease phenotype: comparison with similar cases from the literature

Human prion diseases can be sporadic, inherited or acquired by infection and show considerable phenotypic heterogeneity. We describe the clinical, histopathological and pathological prion protein (PrPSc) characteristics of a Dutch family with a novel 7-octapeptide repeat insertion (7-OPRI) in PRNP, the gene encoding the prion protein (PrP). Clinical features were available in four, neuropathological features in three and biochemical characteristics in two members of this family. The clinical phenotype was characterized by slowly progressive cognitive decline, personality change, lethargy, depression with anxiety and panic attacks, apraxia and a hypokinetic-rigid syndrome. Neuropathological findings consisted of numerous multi- and unicentric amyloid plaques throughout the cerebrum and cerebellum with varying degrees of spongiform degeneration. Genetic and molecular studies were performed in two male family members. One of them was homozygous for valine and the other heterozygous for methionine and valine at codon 129 of PRNP. Sequence analysis identified a novel 168 bp insertion [R2–R2–R2–R2–R3g–R2–R2] in the octapeptide repeat region of PRNP. Both patients carried the mutation on the allele with valine at codon 129. Western blot analysis showed type 1 PrPSc in both patients and detected a smaller ~8 kDa PrPSc fragment in the cerebellum in one patient. The features of this Dutch kindred define an unusual neuropathological phenotype and a novel PRNP haplotype among the previously documented 7-OPRI mutations, further expanding the spectrum of genotype–phenotype correlations in inherited prion diseases.

Prion protein gene (PRNP) polymorphisms in native Chinese cattle

Polymorphisms in four regions of the bovine prion protein gene (PRNP) confer susceptibility to bovine spongiform encephalopathy (BSE). These polymorphisms include a 23-bp insertion/deletion (indel) in the promoter region, a 12-bp indel in intron 1, an octapeptide repeat or 24-bp indel in the open reading frame, and a single nucleotide polymorphism (SNP) in the coding region. In this study, we investigated the frequency distributions of genotypes, alleles, and haplotypes at these indel sites in 349 native Chinese cattle and sequence variants in 50 samples. Our results showed that cattle in southern China have low frequencies of the 12-bp deletion allele and the 23-bp deletion / 12-bp deletion haplotype, which have been suggested to be relevant to BSE susceptibility. Interestingly, a significant difference was observed between BSE-affected cattle and healthy Chinese cattle in the 12-bp indel polymorphism. A total of 14 SNPs were discovered in the coding region of PRNP in Chinese cattle. Three of these SNPs were associated with amino acid changes (K3T, P54S, and S154N). The E211K substitution that was recently reported in the US atypical BSE case was not detected in this study.

Computational Studies of Transition Metal Selectivity of Octapeptide Repeat Region of Prion Protein (PrP)

We have presented a detailed theoretical (density functional theory and ONIOM) study on the structure and M-PrP (prion protein) interaction on various prion models, M(PrP) systems (where PrP = HGG, HGGGW x 3H(2)O, and PrP(61-84), and M = Zn, Cu, Ni, Co, Fe, Mn). It was shown that the geometry of the complex [Mn(HGGGW)(H(2)O)] x 2H(2)O is quite different for M = Mn(III) and Mn(II), and partial unfolding occurs only for the M = Mn(III). In [Zn{PrP(61-84)}], Zn(II) forms a bond with carbonyl oxygen of the Pro(84) residue in the axial position. The coordination of transition metal ions to PrP(61-84) induces the significant geometrical changes in the PrP(61-68) and Prp(69-76) octapeptide repeat regions. The Trp(65) and Trp(73) residues come closer to each other. The glutamines Gln(67) and Gln(75) also come closer to one another and result in the formation of a hydrogen bond between the carbonyl carbon of Gln(67) and one of the NH(2) hydrogens of Gln(75). A specific aggregatory effect is found for Co(II) and Mn(II). The relative binding ability of the metal ions increases in the order Zn(II) < Mn(II) < Cu(II) < Fe(II) < Co(II) < Ni(II). The PrP is most distorted upon binding to Co(II) and least distorted upon binding to Zn(II).

PRNP variation in UK sporadic and variant Creutzfeldt Jakob disease highlights genetic risk factors and a novel non-synonymous polymorphism

BackgroundGenetic analysis of the human prion protein gene (PRNP) in suspect cases of Creutzfeldt-Jakob disease (CJD) is necessary for accurate diagnosis and case classification. Previous publications on the genetic variation at the PRNP locus have highlighted the presence of numerous polymorphisms, in addition to the well recognised one at codon 129, with significant variability between geographically distinct populations. It is therefore of interest to consider their influence on susceptibility or the clinico-pathological disease phenotype. This study aimed to characterise the frequency and effect of PRNP open reading frame polymorphisms other than codon 129 in both disease and control samples sourced from the United Kingdom population.MethodsDNA was extracted from blood samples and genetic data obtained by full sequence analysis of the prion protein gene or by restriction fragment length polymorphism analysis using restriction enzymes specific to the gene polymorphism under investigation.Results147 of 166 confirmed cases of variant CJD (vCJD) in the UK have had PRNP codon 129 genotyping and all are methionine homozygous at codon 129; 118 have had full PRNP gene sequencing. Of the latter, 5 cases have shown other polymorphic loci: at codon 219 (2, 1.69%), at codon 202 (2, 1.69%), and a 24 bp deletion in the octapeptide repeat region (1, 0.85%). E219K and D202D were not found in sporadic CJD (sCJD) cases and therefore may represent genetic risk factors for vCJD.Genetic analysis of 309 confirmed UK sCJD patients showed codon 129 genotype frequencies of MM: 59.5% (n = 184), MV: 21.4% (n = 66), and VV: 19.1% (n = 59). Thirteen (4.2%) had the A117A polymorphism, one of which also had the P68P polymorphism, four (1.3%) had a 24 bp deletion, and a single patient had a novel missense variation at codon 167. As the phenotype of this latter case is similar to sCJD and in the absence of a family history of CJD, it is unknown whether this is a form of genetic CJD, or simply a neutral polymorphism.ConclusionsThis analysis of PRNP genetic variation in UK CJD patients is the first to show a comprehensive comparison with healthy individuals (n = 970) from the same population, who were genotyped for the three most common variations (codon 129, codon 117, and 24 bp deletion). These latter two genetic variations were equally frequent in UK sCJD or vCJD cases and a normal (healthy blood donor) UK population.

Prion protein gene polymorphism in healthy and BSE-affected Slovak cattle

Variation of the PrP gene was examined in healthy and BSE-affected Slovak cattle. According to previous studies, the 23-bp indel polymorphism is supposed to be associated with higher susceptibility to BSE. We investigated 301 samples from healthy cattle of various Slovak breeds and 24 samples obtained from tissues of BSE-affected cattle in Slovakia. We examined the PrP gene for the 23-bp indel polymorphism in the putative promoter region, 12-bp indel polymorphism in the first intron of the PrP gene, variations in number of octapeptide repeat units, and presence of the silent AAC>AAT transition in codon 192 within the protein-coding region of the PrP gene. Altogether we found 23 different genotypes in the group of healthy cattle and only 6 genotypes in the group of BSE-affected cattle. Comparison of homozygotes for the 23-bp insertion and heterozygotes showed significant differences (P < 0.05) in genotype distribution between the examined groups. Thereby the homozygous insertion genotype at the 23-bp indel polymorphism site in the promoter region of the prion protein gene seems to have a protective effect against BSE.

Gene and haplotype polymorphisms of the Prion gene (PRNP) in Japanese Brown, Japanese native and Holstein cattle

Polymorphisms in the prion protein gene (PRNP) are known to be associated with transmissible spongiform encephalopathies in human, sheep and goats. There is tentative association between PRNP promoter polymorphism and bovine spongiform encephalopathy (BSE) susceptibility in cattle. In this study, we genotyped for six bovine PRNP polymorphic sites including a 23-bp indel in the promoter, a 12-bp indel in the intron 1, two nonsynonymous single nucleotide polymorphisms (SNPs), octapeptide repeats in the coding region and a 14-bp indel in the 3'-untranslated region in 178 animals representing Japanese Brown, Kuchinoshima feral, Mishima, Japanese Shorthorn and Holstein. In 64 Japanese Brown cattle, three indel sites were polymorphic. All of the six sites were monomorphic in Kuchinoshima. The 23-bp and 12-bp indel sites were polymorphic in Mishima cattle. The 23-bp and 14-bp indel sites were polymorphic in Japanese Shorthorn cattle. Both SNP sites were monomorphic in all cattle examined in this study. At the 23-bp indel site, the genotype frequencies of Japanese Brown and Holstein breeds were similar to that of BSE affected cattle. We estimated 12 different haplotypes from these genotypic data. A '23-12-K6S14+' haplotype was the major haplotype in all populations, whose frequencies ranged from 0.50 to 1.00.

Difference in redox behaviors between copper-binding octarepeat and nonoctarepeat sites in prion protein

We studied the redox behavior of copper-binding sites in prion protein (PrP) to clarify copper's role in the pathological mechanism underlying prion diseases. We investigated the coordination structures, binding affinities, and redox potentials of copper-binding peptide fragments derived from the N-terminal domain of PrP by density functional theory calculations. We used four models for copper-binding moieties in PrP(60-96): two were derived from the PHGGGWGQ octapeptide repeat region of PrP(60-91), and the others were tripeptide Gly-Thr-His fragments derived from the copper-binding nonoctarepeat site around His96. We found that such PrP-derived copper-binding complexes exhibit conformationally dependent redox behavior; for example, the copper-binding complex derived from the octarepeat region tends to possess high reduction potential for the Cu(II)/Cu(I) couple, exceeding 0 V versus the standard hydrogen electrode, whereas the copper-binding nonoctarepeat model around His96 tends to possess high oxidation potential for the Cu(II)/Cu(III) couple and stabilize the higher-valent Cu(III) state. It is possible that such distinct redox activities of a copper-binding PrP are involved in the mechanism underlying prion diseases.

Sequence analysis of the prion protein gene in Mongolian gazelles (Procapra gutturosa)

Prion diseases are a group of human and animal neurodegenerative conditions, which are caused by the deposition of an abnormal isoform prion protein (PrPSc) encoded by a single copy prion protein gene (Prnp). In sheep, genetic variations of Prnp were found to be associated with the incubation period, susceptibility, and species barrier to the scrapie disease. We investigated the sequence and polymorphisms of the prion protein gene of Mongolian gazelles (gPrnp). gPrnp gene sequence analysis of blood samples from 26 Mongolian gazelles showed high identity within species. The gPrnp gene was closely related to the Prnp genes of Thomson’s gazelle, blackbuck, and cattle with 100, 100, and 98.5% identity, respectively, whereas the gPrnp gene with a deletion was closely related to the Prnp genes of wildebeest, Western roe deer, and sheep with 99.3, 99.3, and 98.9% identity, respectively. Polymorphisms of the open reading frame of Prnp as amino acid substitutions were detected at codons 119(N --> S), 143(S --> G) or 160(Y --> H), 172(V --> A), 182(N --> S) and 221(V --> A). There was also deletion of one octapeptide repeat at the N-terminal octapeptide repeat region. The polymorphisms of gPrnp will assist the study of prion disease pathogenesis, resistance, and cross species transmission.

Copper and nickel binding in multi-histidinic peptide fragments

Multi-histidinic peptides have been investigated for Cu(II) and Ni(II) binding. We present spectroscopic evidence that, at low pH and from sub-stoichiometric to stoichiometric amounts of metals, macrochelate and multi-histidinic Cu(II) and Ni(II) complexes form; but, from neutral pH and above, both copper and nickel bind to individual histidine residues. NMR, EPR, UV-Visible (UV-Vis) and UV-Visible CD spectroscopy were used to understand about the variety of complexes obtained at low pHs, where amide deprotonation and coordination is unfavoured. A structural transition between two coordination geometries, as the pH is raised, was observed. Metal binds to N(delta) of histidine imidazole when main-chain coordination is involved and coordinates via N(epsilon) under mildly acidic conditions and sub-stoichiometric amounts of metals. From EPR results a distortion from planarity has been evidenced for the Cu(II) multi-histidinic macrochelate systems, which may be relevant to biological activity. The behaviour of our peptides was comparable to the pH dependent effect on Cu(II) coordination observed in octapeptide repeat domain in prion proteins and in amyloid precursor peptides involved in Alzheimer's disease. Changes in pH and levels of metal affect coordination mode and can have implications for the affinity, folding and redox properties of proteins and peptide fragments.