The Contribution of ArsB to Arsenic Resistance in Campylobacter jejuni

Arsenic, a toxic metalloid, exists in the natural environment and its organic form is approved for use as a feed additive for animal production. As a major foodborne pathogen of animal origin, Campylobacter is exposed to arsenic selection pressure in the food animal production environments. Previous studies showed that Campylobacter isolates from poultry were highly resistant to arsenic compounds and a 4-gene operon (containing arsP, arsR, arsC, and acr3) was associated with arsenic resistance in Campylobacter. However, this 4-gene operon is only present in some Campylobacter isolates and other arsenic resistance mechanisms in C. jejuni have not been characterized. In this study, we determined the role of several putative arsenic resistance genes including arsB, arsC2, and arsR3 in arsenic resistance in C. jejuni and found that arsB, but not the other two genes, contributes to the resistance to arsenite and arsenate. Inactivation of arsB in C. jejuni resulted in 8- and 4-fold reduction in the MICs of arsenite and arsenate, respectively, and complementation of the arsB mutant restored the MIC of arsenite. Additionally, overexpression of arsB in C. jejuni 11168 resulted in a 16-fold increase in the MIC of arsenite. PCR analysis of C. jejuni isolates from different animals hosts indicated that arsB and acr3 (the 4-gene operon) are widely distributed in various C. jejuni strains, suggesting that Campylobacter requires at least one of the two genes for adaptation to arsenic-containing environments. These results identify ArsB as an alternative mechanism for arsenic resistance in C. jejuni and provide new insights into the adaptive mechanisms of Campylobacter in animal food production environments.     

Lactobacillus gasseri SBT2055 Reduces Infection by and Colonization of Campylobacter jejuni

Campylobacter is a normal inhabitant of the chicken gut. Pathogenic infection with this organism in humans is accompanied by severe inflammation of the intestinal mucosal surface. The aim of this study was to evaluate the ability of Lactobacillus gasseri SBT2055 (LG2055) to inhibit the adhesion and invasion of Campylobacter jejuni in vitro and to suppress C. jejuni colonization of chicks in vivo. Pretreatment with LG2055 significantly reduced adhesion to and invasion of a human epithelial cell line, Intestine 407, by C. jejuni 81–176. Methanol (MeOH)-fixed LG2055 also reduced infection by C. jejuni 81–176. However, proteinase K (ProK)-treated LG2055 eliminated the inhibitory effects. Moreover, LG2055 co-aggregated with C. jejuni 81–176. ProK treatment prevented this co-aggregation, indicating that the co-aggregation phenotype mediated by the proteinaceous cell-surface components of LG2055 is important for reducing C. jejuni 81–176 adhesion and invasion. In an in vivo assay, oral doses of LG2055 were administered to chicks daily for 14 days after oral inoculation with C. jejuni 81–176. At 14 days post-inoculation, chicks treated with LG2055 had significantly reduced cecum colonization by C. jejuni. Reduction in the number of C. jejuni 81–176 cells adhering to and internalized by human epithelial cells demonstrated that LG2055 is an organism that effectively and competitively excludes C. jejuni 81–176. In addition, the results of the chick colonization assay suggest that treatment with LG2055 could be useful in suppressing C. jejuni colonization of the chicks at early growth stages.     

Hygromycin B and Apramycin Antibiotic Resistance Cassettes for Use in Campylobacter jejuni

Campylobacter jejuni genetic manipulation is restricted by the limited number of antibiotic resistance cassettes available for use in this diarrheal pathogen. In this study, two antibiotic resistance cassettes were developed, encoding for hygromycin B and apramycin resistance, for use in mutagenesis or for selection of gene expression and complementation constructs in C. jejuni. First, the marker genes were successfully modified to allow for insertional mutagenesis or deletion of a gene-of-interest, and were bracketed with restriction sites for the facilitation of site-specific cloning. These hygromycin B and apramycin markers are encoded by plasmids pAC1H and pAC1A, respectively. We also modified an insertional gene-delivery vector to create pRRH and pRRA, containing the hygromycin B and apramycin resistance genes, and 3 unique restriction sites for the directional introduction of genes into the conserved multi-copy rRNA gene clusters of the C. jejuni chromosome. We determined the effective antibiotic concentrations required for selection, and established that no harmful effects or fitness costs were associated with carrying hygromycin B or apramycin resistance under standard C. jejuni laboratory conditions. Using these markers, the arylsulfatase reporter gene astA was deleted, and the ability to genetically complement the astA deletion using pRRH and pRRA for astA gene insertion was demonstrated. Furthermore, the relative levels of expression from the endogenous astA promoter were compared to that of polycistronic mRNA expression from the constitutive promoter upstream of the resistance gene. The development of additional antibiotic resistance cassettes for use in Campylobacter will enable multiple gene deletion and expression combinations as well as more in-depth study of multi-gene systems important for the survival and pathogenesis of this important bacterium.     

Role of Alkyl Hydroperoxide Reductase (AhpC) in the Biofilm Formation of Campylobacter jejuni

Biofilm formation of Campylobacter jejuni, a major cause of human gastroenteritis, contributes to the survival of this pathogenic bacterium in different environmental niches; however, molecular mechanisms for its biofilm formation have not been fully understood yet. In this study, the role of oxidative stress resistance in biofilm formation was investigated using mutants defective in catalase (KatA), superoxide dismutase (SodB), and alkyl hydroperoxide reductase (AhpC). Biofilm formation was substantially increased in an ahpC mutant compared to the wild type, and katA and sodB mutants. In contrast to the augmented biofilm formation of the ahpC mutant, a strain overexpressing ahpC exhibited reduced biofilm formation. A perR mutant and a CosR-overexpression strain, both of which upregulate ahpC, also displayed decreased biofilms. However, the introduction of the ahpC mutation to the perR mutant and the CosR-overexpression strain substantially enhanced biofilm formation. The ahpC mutant accumulated more total reactive oxygen species and lipid hydroperoxides than the wild type, and the treatment of the ahpC mutant with antioxidants reduced biofilm formation to the wild-type level. Confocal microscopy analysis showed more microcolonies were developed in the ahpC mutant than the wild type. These results successfully demonstrate that AhpC plays an important role in the biofilm formation of C. jejuni.     

Comparison of Predicted Epimerases and Reductases of the Campylobacter jejuni d-altro- and l-gluco-Heptose Synthesis Pathways

Uniquely modified heptoses found in surface carbohydrates of bacterial pathogens are potential therapeutic targets against such pathogens. Our recent biochemical characterization of the GDP-6-deoxy-d-manno- and GDP-6-deoxy-d-altro-heptose biosynthesis pathways has provided the foundation for elucidation of the more complex l-gluco-heptose synthesis pathway of Campylobacter jejuni strain NCTC 11168. In this work we use GDP-4-keto,6-deoxy-d-lyxo-heptose as a surrogate substrate to characterize three enzymes predicted to be involved in this pathway: WcaG_NCTC (also known as Cj1427), MlghB (Cj1430), and MlghC (Cj1428). We compare them with homologues involved in d-altro-heptose production: WcaG₈₁₁₇₆ (formerly WcaG), DdahB (Cjj1430), and DdahC (Cjj1427). We show that despite high levels of similarity, the enzymes have pathway-specific catalytic activities and substrate specificities. MlghB forms three products via C3 and C5 epimerization activities, whereas its DdahB homologue only had C3 epimerase activity along its cognate pathway. MlghC is specific for the double C3/C5 epimer generated by MlghB and produces l-gluco-heptose via stereospecific C4 reductase activity. In contrast, its homologue DdahC only uses the C3 epimer to yield d-altro-heptose via C4 reduction. Finally, we show that WcaG_NCTC is not necessary for l-gluco-heptose synthesis and does not affect its production by MlghB and MlghC, in contrast to its homologue WcaG₈₁₁₇₆, that has regulatory activity on d-altro-heptose synthesis. These studies expand our fundamental understanding of heptose modification, provide new glycobiology tools to synthesize novel heptose derivatives with biomedical applications, and provide a foundation for the structure function analysis of these enzymes.     

Characterisation of a Multi-ligand Binding Chemoreceptor CcmL (Tlp3) of Campylobacter jejuni

Campylobacter jejuni is the leading cause of human gastroenteritis worldwide with over 500 million cases annually. Chemotaxis and motility have been identified as important virulence factors associated with C. jejuni colonisation. Group A transducer-like proteins (Tlps) are responsible for sensing the external environment for bacterial movement to or away from a chemical gradient or stimulus. In this study, we have demonstrated Cj1564 (Tlp3) to be a multi-ligand binding chemoreceptor and report direct evidence supporting the involvement of Cj1564 (Tlp3) in the chemotaxis signalling pathway via small molecule arrays, surface plasmon and nuclear magnetic resonance (SPR and NMR) as well as chemotaxis assays of wild type and isogenic mutant strains. A modified nutrient depleted chemotaxis assay was further used to determine positive or negative chemotaxis with specific ligands. Here we demonstrate the ability of Cj1564 to interact with the chemoattractants isoleucine, purine, malic acid and fumaric acid and chemorepellents lysine, glucosamine, succinic acid, arginine and thiamine. An isogenic mutant of cj1564 was shown to have altered phenotypic characteristics of C. jejuni, including loss of curvature in bacterial cell shape, reduced chemotactic motility and an increase in both autoagglutination and biofilm formation. We demonstrate Cj1564 to have a role in invasion as in in vitro assays the tlp3 isogenic mutant has a reduced ability to adhere and invade a cultured epithelial cell line; interestingly however, colonisation ability of avian caeca appears to be unaltered. Additionally, protein-protein interaction studies revealed signal transduction initiation through the scaffolding proteins CheV and CheW in the chemotaxis sensory pathway. This is the first report characterising Cj1564 as a multi-ligand receptor for C. jejuni, we therefore, propose to name this receptor CcmL, Campylobacter chemoreceptor for multiple ligands. In conclusion, this study identifies a novel multifunctional role for the C. jejuni CcmL chemoreceptor and illustrates its involvement in the chemotaxis pathway and subsequent survival of this organism in the host.     

Effects of Lipooligosaccharide Inner Core Truncation on Bile Resistance and Chick Colonization by Campylobacter jejuni

Campylobacter jejuni is the most common bacterium that causes diarrhea worldwide, and chickens are considered the main reservoir of this pathogen. This study investigated the effects of serial truncation of lipooligosaccharide (LOS), a major component of the outer membrane of C. jejuni, on its bile resistance and intestinal colonization ability in chickens. Genes encoding manno-heptose synthetases or glycosyltransferases were inactivated to generate isogenic mutants. Serial truncation of the LOS core oligosaccharide caused a stepwise increase in susceptibilities of two C. jejuni strains, NCTC 11168 and 81-176, to bile acids. Inactivation of hldE, hldD, or waaC caused severe truncation of the core oligosaccharide, which greatly increased the susceptibility to bile acids. Both wild-type strains grew normally in chicken intestinal extracts, whereas the mutants with severe oligosaccharide truncation were not detected 12 h after inoculation. These mutants attained viable bacterial counts in the bile acid-free extracts 24 h after inoculation. The wild-type strain 11-164 was present in the cecal contents at >10⁷ CFU/g on 5 days after challenge infection and after this time period, whereas its hldD mutant was present at <10³ CFU/g throughout the experimental period. Trans-complementation of the hldD mutant with the wild-type hldD allele completely restored the in vivo colonization level to that of the wild-type strain. Mutants with a shorter LOS had higher hydrophobicities. Thus, the length of the LOS core oligosaccharide affected the surface hydrophobicity and bile resistance of C. jejuni as well as its ability to colonize chicken intestines.     

Polyphosphate Kinase 2: A Novel Determinant of Stress Responses and Pathogenesis in Campylobacter jejuni

Background

Inorganic polyphosphate (poly P) plays an important role in stress tolerance and virulence in many bacteria. PPK1 is the principal enzyme involved in poly P synthesis, while PPK2 uses poly P to generate GTP, a signaling molecule that serves as an alternative energy source and a precursor for various physiological processes. Campylobacter jejuni, an important cause of foodborne gastroenteritis in humans, possesses homologs of both ppk1 and ppk2. ppk1 has been previously shown to impact the pathobiology of C. jejuni.

Methodology/Principal Findings

Here, we demonstrate for the first time that the deletion of ppk2 in C. jejuni resulted in a significant decrease in poly P-dependent GTP synthesis, while displaying an increased intracellular ATP:GTP ratio. The Δppk2 mutant exhibited a significant survival defect under osmotic, nutrient, aerobic, and antimicrobial stresses and displayed an enhanced ability to form static biofilms. However, the Δppk2 mutant was not defective in poly P and ppGpp synthesis suggesting that PPK2-mediated stress tolerance is not ppGpp-mediated. Importantly, the Δppk2 mutant was significantly attenuated in invasion and intracellular survival within human intestinal epithelial cells as well as in chicken colonization.

Conclusions/Significance

Taken together, we have highlighted the role of PPK2 as a novel pathogenicity determinant that is critical for C. jejuni survival, adaptation, and persistence in the host environments. PPK2 is absent in humans and animals; therefore, can serve as a novel target for therapeutic intervention of C. jejuni infections.     

Prevention of Biofilm Formation and Removal of Existing Biofilms by Extracellular DNases of Campylobacter jejuni

The fastidious nature of the foodborne bacterial pathogen Campylobacter jejuni contrasts with its ability to survive in the food chain. The formation of biofilms, or the integration into existing biofilms by C. jejuni, is thought to contribute to food chain survival. As extracellular DNA (eDNA) has previously been proposed to play a role in C. jejuni biofilms, we have investigated the role of extracellular DNases (eDNases) produced by C. jejuni in biofilm formation. A search of 2791 C. jejuni genomes highlighted that almost half of C. jejuni genomes contains at least one eDNase gene, but only a minority of isolates contains two or three of these eDNase genes, such as C. jejuni strain RM1221 which contains the cje0256, cje0566 and cje1441 eDNase genes. Strain RM1221 did not form biofilms, whereas the eDNase-negative strains NCTC 11168 and 81116 did. Incubation of pre-formed biofilms of NCTC 11168 with live C. jejuni RM1221 or with spent medium from a RM1221 culture resulted in removal of the biofilm. Inactivation of the cje1441 eDNase gene in strain RM1221 restored biofilm formation, and made the mutant unable to degrade biofilms of strain NCTC 11168. Finally, C. jejuni strain RM1221 was able to degrade genomic DNA from C. jejuni NCTC 11168, 81116 and RM1221, whereas strain NCTC 11168 and the RM1221 cje1441 mutant were unable to do so. This was mirrored by an absence of eDNA in overnight cultures of C. jejuni RM1221. This suggests that the activity of eDNases in C. jejuni affects biofilm formation and is not conducive to a biofilm lifestyle. These eDNases do however have a potential role in controlling biofilm formation by C. jejuni strains in food chain relevant environments.     

Peptidoglycan-Modifying Enzyme Pgp1 Is Required for Helical Cell Shape and Pathogenicity Traits in Campylobacter jejuni

The impact of bacterial morphology on virulence and transmission attributes of pathogens is poorly understood. The prevalent enteric pathogen Campylobacter jejuni displays a helical shape postulated as important for colonization and host interactions. However, this had not previously been demonstrated experimentally. C. jejuni is thus a good organism for exploring the role of factors modulating helical morphology on pathogenesis. We identified an uncharacterized gene, designated pgp1 (peptidoglycan peptidase 1), in a calcofluor white-based screen to explore cell envelope properties important for C. jejuni virulence and stress survival. Bioinformatics showed that Pgp1 is conserved primarily in curved and helical bacteria. Deletion of pgp1 resulted in a striking, rod-shaped morphology, making pgp1 the first C. jejuni gene shown to be involved in maintenance of C. jejuni cell shape. Pgp1 contributes to key pathogenic and cell envelope phenotypes. In comparison to wild type, the rod-shaped pgp1 mutant was deficient in chick colonization by over three orders of magnitude and elicited enhanced secretion of the chemokine IL-8 in epithelial cell infections. Both the pgp1 mutant and a pgp1 overexpressing strain – which similarly produced straight or kinked cells – exhibited biofilm and motility defects. Detailed peptidoglycan analyses via HPLC and mass spectrometry, as well as Pgp1 enzyme assays, confirmed Pgp1 as a novel peptidoglycan DL-carboxypeptidase cleaving monomeric tripeptides to dipeptides. Peptidoglycan from the pgp1 mutant activated the host cell receptor Nod1 to a greater extent than did that of wild type. This work provides the first link between a C. jejuni gene and morphology, peptidoglycan biosynthesis, and key host- and transmission-related characteristics.     

Flagella-Mediated Adhesion and Extracellular DNA Release Contribute to Biofilm Formation and Stress Tolerance of Campylobacter jejuni

Campylobacter jejuni is a leading cause of foodbourne gastroenteritis, despite fragile behaviour under standard laboratory conditions. In the environment, C. jejuni may survive within biofilms, which can impart resident bacteria with enhanced stress tolerance compared to their planktonic counterparts. While C. jejuni forms biofilms in vitro and in the wild, it had not been confirmed that this lifestyle confers stress tolerance. Moreover, little is understood about molecular mechanisms of biofilm formation in this pathogen. We previously found that a ΔcprS mutant, which carries a deletion in the sensor kinase of the CprRS two-component system, forms enhanced biofilms. Biofilms were also enhanced by the bile salt deoxycholate and contained extracellular DNA. Through more in-depth analysis of ΔcprS and WT under conditions that promote or inhibit biofilms, we sought to further define this lifestyle for C. jejuni. Epistasis experiments with ΔcprS and flagellar mutations (ΔflhA, ΔpflA) suggested that initiation is mediated by flagellum-mediated adherence, a process which was kinetically enhanced by motility. Lysis was also observed, especially under biofilm-enhancing conditions. Microscopy suggested adherence was followed by release of eDNA, which was required for biofilm maturation. Importantly, inhibiting biofilm formation by removal of eDNA with DNase decreased stress tolerance. This work suggests the biofilm lifestyle provides C. jejuni with resilience that has not been apparent from observation of planktonic bacteria during routine laboratory culture, and provides a framework for subsequent molecular studies of C. jejuni biofilms.     

Identification of a Novel G2073A Mutation in 23S rRNA in Amphenicol-Selected Mutants of Campylobacter jejuni

Objectives

This study was conducted to examine the development and molecular mechanisms of amphenicol resistance in Campylobacter jejuni by using in vitro selection with chloramphenicol and florfenicol. The impact of the resistance development on growth rates was also determined using in vitro culture.

Methods

Chloramphenicol and florfenicol were used as selection agents to perform in vitro stepwise selection. Mutants resistant to the selective agents were obtained from the selection process. The mutant strains were compared with the parent strain for changes in MICs and growth rates. The 23S rRNA gene and the L4 and L22 ribosomal protein genes in the mutant strains and the parent strain were amplified and sequenced to identify potential resistance-associated mutations.

Results

C. jejuni strains that were highly resistant to chloramphenicol and florfenicol were obtained from in vitro selection. A novel G2073A mutation in all three copies of the 23S rRNA gene was identified in all the resistant mutants examined, which showed resistance to both chloramphenicol and florfenicol. In addition, all the mutants selected by chloramphenicol also exhibited the G74D modification in ribosomal protein L4, which was previously shown to confer a low-level erythromycin resistance in Campylobacter species. The mutants selected by florfenicol did not have the G74D mutation in L4. Notably, the amphenicol-resistant mutants also exhibited reduced susceptibility to erythromycin, suggesting that the selection resulted in cross resistance to macrolides.

Conclusions

This study identifies a novel point mutation (G2073A) in 23S rRNA in amphenicol-selected mutants of C. jejuni. Development of amphenicol resistance in Campylobacter likely incurs a fitness cost as the mutant strains showed slower growth rates in antibiotic-free media.     

Peripheral CD4+ T Cell Cytokine Responses Following Human Challenge and Re-Challenge with Campylobacter jejuni

Campylobacter jejuni is a leading cause of human gastroenteritis worldwide; however, our understanding of the human immune response to C. jejuni infection is limited. A previous human challenge model has shown that C. jejuni elicits IFNγ production by peripheral blood mononuclear cells, a response associated with protection from clinical disease following re-infection. In this study, we investigate T lymphocyte profiles associated with campylobacteriosis using specimens from a new human challenge model in which C. jejuni-naïve subjects were challenged and re-challenged with C. jejuni CG8421. Multiparameter flow cytometry was used to investigate T lymphocytes as a source of cytokines, including IFNγ, and to identify cytokine patterns associated with either campylobacteriosis or protection from disease. Unexpectedly, all but one subject evaluated re-experienced campylobacteriosis after re-challenge. We show that CD4⁺ T cells make IFNγ and other pro-inflammatory cytokines in response to infection; however, multifunctional cytokine response patterns were not found. Cytokine production from peripheral CD4⁺ T cells was not enhanced following re-challenge, which may suggest deletion or tolerance. Evaluation of alternative paradigms or models is needed to better understand the immune components of protection from campylobacteriosis.     

Synthesis and Biological Evaluation of some Acyclic Nucleoside Cyclic Phosphoramidate Derivatives

Abstract

The acyclic nucleosides 2 were treated with 2-chloro-3-methyl-1-oxa-3-aza-2-phosphacyclopentane (3) in the presence of diisopropylethylamine to give the corresponding phosphoramidite derivatives (4). The phosphoramidite intermediates (4) were oxidized with m-chloroperbenzoic acid to the phosphoramidate derivatives (5). Treatment of 5a,b with ZnBr₂ in CH₃NO₂ gave the corresponding acyclic nucleoside cyclic phosphoramidates (6a,b). Attempts to desilylation of 5c by tetrabutylammonium fluoride (TBAF) resulted in opening of the phosphoramidate ring. The newly synthesized compounds were evaluated for antiviral and antitumor cell activity.     

Biological characterization of Campylobacter fetus lipopolysaccharides

Abstract Ten patients with chronic liver disease, seven healthy seropositive individuals with a remote history of rubella, and three patients with acute rubella were examined for serum levels of IgG subclasses and subclass antibodies against rubella virus structural proteins. One patient with AICAH had no detectable total or rubella specific IgG3 or IgG4. The liver disease patients were hypergammaglobulinemic and had greatly raised IgG1 levels. Patients with acute rubella lacked antibodies to the rubella virus E2 protein and showed no IgG4 antibody response. The liver disease patients showed a somewhat weaker IgG4 antibody response against the core (C) protein than healthy controls. However, differences are suggested within the subclasses in antibody reactivity against the individual rubella virus antigens. It is concluded that test systems that discriminate reactivities against individual antigens have to be used for characterization of viral antibody subclass profiles.     

Bacteriophage Receptor Binding Protein Based Assays for the Simultaneous Detection of Campylobacter jejuni and Campylobacter coli

Campylobacter jejuni and Campylobacter coli are the most common bacterial causes of foodborne gastroenteritis which is occasionally followed by a debilitating neuropathy known as Guillain-Barré syndrome. Rapid and specific detection of these pathogens is very important for effective control and quick treatment of infection. Most of the diagnostics available for these organisms are time consuming and require technical expertise with expensive instruments and reagents to perform. Bacteriophages bind to their host specifically through their receptor binding proteins (RBPs), which can be exploited for pathogen detection. We recently sequenced the genome of C. jejuni phage NCTC12673 and identified its putative host receptor binding protein, Gp047. In the current study, we localized the receptor binding domain to the C-terminal quarter of Gp047. CC-Gp047 could be produced recombinantly and was capable of agglutinating both C. jejuni and C. coli cells unlike the host range of the parent phage which is limited to a subset of C. jejuni isolates. The agglutination procedure could be performed within minutes on a glass slide at room temperature and was not hindered by the presence of buffers or nutrient media. This agglutination assay showed 100% specificity and the sensitivity was 95% for C. jejuni (n = 40) and 90% for C. coli (n = 19). CC-Gp047 was also expressed as a fusion with enhanced green fluorescent protein (EGFP). Chimeric EGFP_CC-Gp047 was able to specifically label C. jejuni and C. coli cells in mixed cultures allowing for the detection of these pathogens by fluorescent microscopy. This study describes a simple and rapid method for the detection of C. jejuni and C. coli using engineered phage RBPs and offers a promising new diagnostics platform for healthcare and surveillance laboratories.     

Biological Roles of Prion Domains

In vivo amyloid formation is a widespread phenomenon in eukaryotes. Self-perpetuating amyloids provide a basis for the infectious or heritable protein isoforms (prions). At least for some proteins, amyloid-forming potential is conserved in evolution despite divergence of the amino acid (aa) sequences. In some cases, prion formation certainly represents a pathological process leading to a disease. However, there are several scenarios in which prions and other amyloids or amyloid-like aggregates are either shown or suspected to perform positive biological functions. Proven examples include self/nonself recognition, stress defense and scaffolding of other (functional) polymers. The role of prion-like phenomena in memory has been hypothesized. As an additional mechanism of heritable change, prion formation may in principle contribute to heritable variability at the population level. Moreover, it is possible that amyloid-based prions represent by-products of the transient feedback regulatory circuits, as normal cellular function of at least some prion proteins is decreased in the prion state.     

Biological Roles of Prion Domains

In vivo amyloid formation is a widespread phenomenon in eukaryotes. Self-perpetuating amyloids provide a basis for the infectious or heritable protein isoforms (prions). At least for some proteins, amyloid-forming potential is conserved in evolution despite divergence of the amino acid (aa) sequences. In some cases, prion formation certainly represents a pathological process leading to a disease. However, there are several scenarios in which prions and other amyloids or amyloid-like aggregates are either shown or suspected to perform positive biological functions. Proven examples include self/nonself recognition, stress defense and scaffolding of other (functional) polymers. The role of prion-like phenomena in memory has been hypothesized. As an additional mechanism of heritable change, prion formation may in principle contribute to heritable variability at the population level. Moreover, it is possible that amyloid-based prions represent by-products of the transient feedback regulatory circuits, as normal cellular function of at least some prion proteins is decreased in the prion state.Key Words: amyloid, amyloidosis, epigenetic, evolution, inheritance, mammals, misfolding, protein, stress, yeast