Amino acid sequence of the Felis catus prion protein

Novel Polymorphisms and Genetic Features of the Prion Protein Gene (PRNP) in Cats, Hosts of Feline Spongiform Encephalopathy

Prion diseases are fatal neurodegenerative disorders characterized by vacuolation and gliosis in the brain. Prion diseases have been reported in several mammals, and genetic polymorphisms of the prion protein gene (PRNP) play an essential role in the vulnerability of prion diseases. However, to date, investigations of PRNP polymorphisms are rare in cats, which are the major host of feline spongiform encephalopathy (FSE). Thus, we investigated the genetic polymorphisms of the cat PRNP gene and analyzed the structural characteristics of the PrP of cats compared to those of dog, prion disease-resistant animal. To investigate the genetic variations of the cat PRNP gene in 208 cats, we performed amplicon sequencing and examined the genotype, allele and haplotype frequencies of cat PRNP polymorphisms. We evaluated the influence of cat PRNP polymorphisms using PolyPhen-2, PANTHER, PROVEAN and AMYCO. In addition, we carried out structural analysis of cat PrP according to the allele of nonsynonymous single nucleotide polymorphism (SNP) (c.457G > A, Glu153Lys) using Swiss-PdbViewer. Finally, we compared the structural differences between cat and canine PrPs for SNPs associated with prion disease resistance in dogs. We identified a total of 15 polymorphisms, including 14 novel SNPs and one insertion/deletion polymorphism (InDel). Among them, Glu153Lys was predicted to affect the structural stability and amyloid propensity of cat PrP. In addition, asparagine at codon 166 of cat PrP was predicted to have longer hydrogen bond than aspartic acid at codon 163 of canine PrP. Furthermore, substitution to dog-specific amino acids in cat PrP showed an increase in structural stability. To the best of our knowledge, this is the first study regarding the structural characteristics of cat PRNP gene.

Molecular dynamics studies of dog prion protein wild-type and its D159N mutant

Prion diseases (e.g. 'mad cow' disease in cattle, chronic wasting disease in deer and elk, Creutzfeldt-Jakob disease in humans) have been a major public health concern affecting humans and almost all animals. However, dogs are strongly resistant to prion diseases. Recently, through transgenic techniques, it was reported that the single (surface) residue D159 is sufficient to confer protection against protein conformational change and pathogenesis, thus provides conformational stability for dog prion protein. This made a big breakthrough in dog prion protein research field. For dog prion protein, another advancement is the produce of its NMR structure in 2005. However, all these breakthroughs are still short of enough structural informatics of dog prion protein. This paper studies dog prion protein wild-type and D159N mutant through molecular dynamics (MD) techniques. Our MD results reveal sufficient structural informatics on the residue at position 159 to understand the mechanism underlying the resistance to prion diseases of dogs. The structural informatics of this paper should be very useful for the medicinal treatment of prion diseases.Communicated by Ramaswamy H. Sarma.

Genetic predictions of prion disease susceptibility in carnivore species based on variability of the prion gene coding region

Mammalian species vary widely in their apparent susceptibility to prion diseases. For example, several felid species developed prion disease (feline spongiform encephalopathy or FSE) during the bovine spongiform encephalopathy (BSE) epidemic in the United Kingdom, whereas no canine BSE cases were detected. Whether either of these or other groups of carnivore species can contract other prion diseases (e.g. chronic wasting disease or CWD) remains an open question. Variation in the host-encoded prion protein (PrP^C) largely explains observed disease susceptibility patterns within ruminant species, and may explain interspecies differences in susceptibility as well. We sequenced and compared the open reading frame of the PRNP gene encoding PrP^C protein from 609 animal samples comprising 29 species from 22 genera of the Order Carnivora; amongst these samples were 15 FSE cases. Our analysis revealed that FSE cases did not encode an identifiable disease-associated PrP polymorphism. However, all canid PrPs contained aspartic acid or glutamic acid at codon 163 which we propose provides a genetic basis for observed susceptibility differences between canids and felids. Among other carnivores studied, wolverine (Gulo gulo) and pine marten (Martes martes) were the only non-canid species to also express PrP-Asp163, which may impact on their prion diseases susceptibility. Populations of black bear (Ursus americanus) and mountain lion (Puma concolor) from Colorado showed little genetic variation in the PrP protein and no variants likely to be highly resistant to prions in general, suggesting that strain differences between BSE and CWD prions also may contribute to the limited apparent host range of the latter.

Proteinase K-resistant material in ARR/VRQ sheep brain affected with classical scrapie is composed mainly of VRQ prion protein

Classical scrapie is a prion disease in sheep and goats. In sheep, susceptibility to disease is genetically influenced by single amino acid substitutions. Genetic breeding programs aimed at enrichment of arginine-171 (171R) prion protein (PrP), the so-called ARR allele, in the sheep population have been demonstrated to be effective in reducing the occurrence of classical scrapie in the field. Understanding the molecular basis for this reduced prevalence would serve the assessment of ARR adaptation. The prion formation mechanism and conversion of PrP from the normal form (PrP(C)) to the scrapie-associated form (PrP(Sc)) could play a key role in this process. Therefore, we investigated whether the ARR allele substantially contributes to scrapie prion formation in naturally infected heterozygous 171Q/R animals. Two methods were applied to brain tissue of 171Q/R heterozygous sheep with natural scrapie to determine the relative amount of the 171R PrP fraction in PrP(res), the proteinase K-resistant PrP(Sc) core. An antibody test differentiating between 171Q and 171R PrP fragments showed that PrP(res) was mostly composed of the 171Q allelotype. Furthermore, using a novel tool for prion research, endoproteinase Lys-C-digested PrP(res) yielded substantial amounts of a nonglycosylated and a monoglycosylated PrP fragment comprising codons 114 to 188. Following two-dimensional gel electrophoresis, only marginal amounts (<9%) of 171R PrP(res) were detected. Enhanced 171R(res) proteolytic susceptibility could be excluded. Thus, these data support a nearly zero contribution of 171R PrP in PrP(res) of 171R/Q field scrapie-infected animals. This is suggestive of a poor adaptation of classical scrapie to this resistance allele under these natural conditions.

Review: contribution of transgenic models to understanding human prion disease

Transgenic mice expressing human prion protein in the absence of endogenous mouse prion protein faithfully replicate human prions. These models reproduce all of the key features of human disease, including long clinically silent incubation periods prior to fatal neurodegeneration with neuropathological phenotypes that mirror human prion strain diversity. Critical contributions to our understanding of human prion disease pathogenesis and aetiology have only been possible through the use of transgenic mice. These models have provided the basis for the conformational selection model of prion transmission barriers and have causally linked bovine spongiform encephalopathy with variant Creutzfeldt-Jakob disease. In the future these models will be essential for evaluating newly identified potentially zoonotic prion strains, for validating effective methods of prion decontamination and for developing effective therapeutic treatments for human prion disease.

Absence of spontaneous disease and comparative prion susceptibility of transgenic mice expressing mutant human prion proteins

Approximately 15 % of human prion disease is associated with autosomal-dominant pathogenic mutations in the prion protein (PrP) gene. Previous attempts to model these diseases in mice have expressed human PrP mutations in murine PrP, but this may have different structural consequences. Here, we describe transgenic mice expressing human PrP with P102L or E200K mutations and methionine (M) at the polymorphic residue 129. Although no spontaneous disease developed in aged animals, these mice were readily susceptible to prion infection from patients with the homotypic pathogenic mutation. However, while variant Creutzfeldt–Jakob disease (CJD) prions transmitted infection efficiently to both lines of mice, markedly different susceptibilities to classical (sporadic and iatrogenic) CJD prions were observed. Prions from E200K and classical CJD M129 homozygous patients, transmitted disease with equivalent efficiencies and short incubation periods in human PrP 200K, 129M transgenic mice. However, mismatch at residue 129 between inoculum and host dramatically increased the incubation period. In human PrP 102L, 129M transgenic mice, short disease incubation periods were only observed with transmissions of prions from P102L patients, whereas classical CJD prions showed prolonged and variable incubation periods irrespective of the codon 129 genotype. Analysis of disease-related PrP (PrP^Sc) showed marked alteration in the PrP^Sc glycoform ratio propagated after transmission of classical CJD prions, consistent with the PrP point mutations directly influencing PrP^Sc assembly. These data indicate that P102L or E200K mutations of human PrP have differing effects on prion propagation that depend upon prion strain type and can be significantly influenced by mismatch at the polymorphic residue 129.

Both Met(109) and Met(112) are utilized for Cu(II) coordination by the amyloidogenic fragment of the human prion protein at physiological pH

The prion protein is a ubiquitous neuronal membrane protein. Misfolding of the prion protein has been implicated in transmissible spongiform encephalopathies (prion diseases). It has been demonstrated that the human prion protein (PrP) is capable of coordinating at least five Cu(II) ions under physiological conditions; four copper binding sites can be found in the octarepeat domain between residues 61 and 91, while another copper binding site can be found in the unstructured "amyloidogenic" domain between residues 91 and 126 PrP(91-126). Herein we expand upon a previous study [J. Shearer, P. Soh, Inorg. Chem. 46 (2007) 710-719] where we demonstrated that the physiologically relevant high affinity Cu(II) coordination site within PrP(91-126) is found between residues 106 and 114. It was shown that Cu(II) is contained within a square planar (N/O)3S coordination environment with one His imidazole ligand (H(111)) and one Met thioether ligand (either M(109) or M(112)). The identity of the Met thioether ligand was not identified in that study. In this study we perform a detailed investigation of the Cu(II) coordination environment within the PrP fragment containing residues 106-114 (PrP(106-114)) involving optical, X-ray absorption, EPR, and fluorescence spectroscopies in conjunction with electronic structure calculations. By using derivatives of PrP(106-114) with systematic Met-->Ile "mutations" we show that the CuII coordination environment within PrP(106-114) is actually comprised of a mixture of two major species; one Cu(II)(N/O)3S center with the M(109) thioether coordinated to CuII and another CuII(N/O)3S center with the M(112) thioether coordinated to CuII. Furthermore, deletion of one or more Met residues from the primary sequence of PrP(106-114) both reduces the CuII affinity of the peptide by two to seven fold, and renders the resulting CuII metallopeptides redox inactive. The biological implications of these findings are discussed.

A prion disease of cervids: chronic wasting disease

Chronic wasting disease (CWD) is a prion disease of deer, elk, and moose, initially recognized in Colorado mule deer. The discovery of CWD beyond the borders of Colorado and Wyoming, in Canada and as far east as New York, has led to its emergence as a prion disease of international importance. Epidemiological studies indicate that CWD is horizontally transmitted among free-ranging animals, potentially indirectly by prion-containing secreta or excreta contaminating the environment. Experimental CWD transmission attempts to other wild and domestic mammals and to transgenic mice expressing the prion protein of cattle, sheep, and humans have shed light on CWD species barriers. Transgenic mice expressing the cervid prion protein have proven useful for assessing the genetic influences of Prnp polymorphisms on CWD susceptibility. Accumulating evidence of CWD pathogenesis indicates that the misfolded prion protein or prion infectivity seems to be widely disseminated in many nonneural organs and in blood. This review highlights contemporary research findings in this prion disease of free-ranging wildlife.

Modeling of protein misfolding in disease

A short review of the results of molecular modeling of prion disease is presented in this chapter. According to the "one-protein theory" proposed by Prusiner, prion proteins are misfolded naturally occurring proteins, which, on interaction with correctly folded proteins may induce misfolding and propagate the disease, resulting in insoluble amyloid aggregates in cells of affected specimens. Because of experimental difficulties in measurements of origin and growth of insoluble amyloid aggregations in cells, theoretical modeling is often the only one source of information regarding the molecular mechanism of the disease. Replica exchange Monte Carlo simulations presented in this chapter indicate that proteins in the native state, N, on interaction with an energetically higher structure, R, can change their conformation into R and form a dimer, R(2). The addition of another protein in the N state to R(2) may lead to spontaneous formation of a trimer, R(3). These results reveal the molecular basis for a model of prion disease propagation or conformational diseases in general.

Comparative analysis of the prion protein (PrP) gene in cetacean species

The partial PrP gene sequence and the deduced protein of eight cetacean species, seven of which have never been reported so far, have been determined in order to extend knowledge of sequence variability of the PrP genes in different species and to aid in speculation on cetacean susceptibility to prions. Both the nucleotide and the deduced amino acid sequences have been analysed in comparison with some of the known mammalian PrPs. Cetacean PrPs present typical features of eutherian PrPs. The PrP gene from the species of the family Delphinidae gave identical nucleic acid sequences, while differences in the PrP gene were found in Balaenopteridae and Ziphidae. The phylogenetic tree resulting from analysis of the cetacean PrP gene sequences, together with reported sequences of some ungulates, carnivores and primates, showed that the PrP gene phylogenesis mirrors the species phylogenesis. The PrP gene of cetaceans is very close to species where natural forms of TSEs are known. From an analysis of the sequences and the phylogenesis of the PrP gene, susceptibility to or occurrence of prion diseases in cetaceans can not be excluded.

Prion protein NMR structures of cats, dogs, pigs, and sheep

The NMR structures of the recombinant cellular form of the prion proteins (PrPC) of the cat (Felis catus), dog (Canis familiaris), and pig (Sus scrofa), and of two polymorphic forms of the prion protein from sheep (Ovis aries) are presented. In all of these species, PrPC consists of an N-terminal flexibly extended tail with approximately 100 amino acid residues and a C-terminal globular domain of approximately 100 residues with three alpha-helices and a short antiparallel beta-sheet. Although this global architecture coincides with the previously reported murine, Syrian hamster, bovine, and human PrPC structures, there are local differences between the globular domains of the different species. Because the five newly determined PrPC structures originate from species with widely different transmissible spongiform encephalopathy records, the present data indicate previously uncharacterized possible correlations between local features in PrPC three-dimensional structures and susceptibility of different mammalian species to transmissible spongiform encephalopathies.