A new continuous epitope of hepatitis A virus

Hepatitis A virus adaptation to cellular shutoff is driven by dynamic adjustments of codon usage and results in the selection of populations with altered capsids

Hepatitis A virus (HAV) has a highly biased and deoptimized codon usage compared to the host cell and fails to inhibit host protein synthesis. It has been proposed that an optimal combination of abundant and rare codons controls the translation speed required for the correct capsid folding. The artificial shutoff host protein synthesis results in the selection of variants containing mutations in the HAV capsid coding region critical for folding, stability, and function. Here, we show that these capsid mutations resulted in changes in their antigenicity; in a reduced stability to high temperature, low pH, and biliary salts; and in an increased efficacy of cell entry. In conclusion, the adaptation to cellular shutoff resulted in the selection of large-plaque-producing virus populations.

IMPORTANCE

HAV has a naturally deoptimized codon usage with respect to that of its cell host and is unable to shut down the cellular translation. This fact contributes to the low replication rate of the virus, in addition to other factors such as the highly inefficient internal ribosome entry site (IRES), and explains the outstanding physical stability of this pathogen in the environment mediated by a folding-dependent highly cohesive capsid. Adaptation to artificially induced cellular transcription shutoff resulted in a redeoptimization of its capsid codon usage, instead of an optimization. These genomic changes are related to an overall change of capsid folding, which in turn induces changes in the cell entry process. Remarkably, the adaptation to cellular shutoff allowed the virus to significantly increase its RNA uncoating efficiency, resulting in the selection of large-plaque-producing populations. However, these populations produced much-debilitated virions.

[Genetic diversity of a rare hepatitis A virus genotype]

PURPOSE OF THE STUDY

Very few is known on genotype II hepatitis A virus (HAV) since it is rarely isolated. From 2002 to 2007, the French observatory of HAV identified six sub-genotype IIA strains of which one from a patient having travelled to West Africa. To investigate the possible African origin of sub-genotype IIA, we determined its prevalence among French travellers in 2008 and characterised its genetic variability.

PATIENTS AND METHODS

The 2008 mandatory notification records were screened for travel to Africa. Viral genotype was determined on the nucleotide sequencing of the VP1/2A junction region. The P1 region coding for capsid proteins was used to compare the genetic diversity of IIA isolates to those of other genotypes.

RESULTS

In 2008, five out of 54 patients returning from West Africa were infected by IIA strains and an additional "autochthonous" case was identified. Two more African cases were identified in 2009. A total of 14 IIA isolates (eight African and six "autochthonous") were analysed. Nucleotide and amino-acid variability of IIA sequences was lower than that of the other genotypes. Phylogenetic analysis revealed the clustering of two "autochthonous" cases with African isolates whereas the other ones belonged to a different lineage.

CONCLUSION

Most IIA strains isolated in France are imported by travellers returning from West Africa. However, the unexplained contamination mode of some "autochthonous" cases suggests another geographical origin to discover or a French reservoir to explore.

Epidemiology and genetic characterization of hepatitis A virus genotype IIA

Three hepatitis A virus (HAV) genotypes, I, II, and III, divided into subtypes A and B, infect humans. Genotype I is the most frequently reported, while genotype II is hardly ever isolated, and its genetic diversity is unknown. From 2002 to 2007, a French epidemiological survey of HAV identified 6 IIA isolates, mostly from patients who did not travel abroad. The possible African origin of IIA strains was investigated by screening the 2008 mandatory notification records of HAV infection: 171 HAV strains from travelers to West Africa and Morocco were identified. Genotyping was performed by sequencing of the VP1/2A junction in 68 available sera. Entire P1 and 5' untranslated regions of IIA strains were compared to reference sequences of other genotypes. The screening retrieved 5 imported IIA isolates. An additional autochthonous case and 2 more African cases were identified in 2008 and 2009, respectively. A total of 14 IIA isolates (8 African and 6 autochthonous) were analyzed. IIA sequences presented lower nucleotide and amino acid variability than other genotypes. The highest variability was observed in the N-terminal region of VP1, while for other genotypes the highest variability was observed at the VP1/2A junction. Phylogenetic analysis identified 2 clusters, one gathering all African and two autochthonous cases and a second including only autochthonous isolates. In conclusion, most IIA strains isolated in France are imported by travelers returning from West Africa. However, the unexplained contamination mode of autochthonous cases suggests another, still to be discovered geographical origin or a French reservoir to be explored.

Hepatitis A virus mutant spectra under the selective pressure of monoclonal antibodies: codon usage constraints limit capsid variability

Severe structural constraints in the hepatitis A virus (HAV) capsid have been suggested as the reason for the lack of emergence of new serotypes in spite of the occurrence of complex distributions of mutants or quasispecies. Analysis of the HAV mutant spectra under immune pressure by the monoclonal antibodies (MAbs) K34C8 (immunodominant site) and H7C27 (glycophorin binding site) has revealed different evolutionary dynamics. Populations composed of complex ensembles of mutants with very low fitness or single dominant mutants with high fitness permit the acquisition of resistance to each of the MAbs, respectively. Deletion mutants were detected as components of the mutant spectra: up to 61 residues, with an average of 19, and up to 83 residues, with an average of 45, in VP3 and VP1 proteins, respectively. A clear negative selection of those replacements affecting the residues encoded by rare codons of the capsid surface has been detected through the present quasispecies analysis, confirming a certain beneficial role of such clusters. Since these clusters are located near or at the epitope regions, the need to maintain such clusters might prevent the emergence of new serotypes.

Full-length sequences of subgenotype IIIA and IIIB hepatitis A virus isolates: Characterization of genotype III HAV genomes

To elucidate the extent of genomic heterogeneity of human hepatitis A virus (HAV) strains and to characterize genotype III HAV strains over the entire genome, the full-length sequence of three subgenotype IIIA isolates (HA-JNG04-90F, HA-JNG08-92F, and HAJ95-8F) and one IIIB isolate (HAJ85-1F) was determined. The HA-JNG04-90F, HA-JNG08-92F, and HAJ95-8F genomes which comprised 7463 or 7464 nt excluding the poly(A) tail, were closest to a reported nearly entire sequence of a IIIA isolate (NOR-21) with identities of 94.4-97.8% over the entire ORF sequence, and the HAJ85-1 genome (7462 nt) to HA-JNG06-90F of IIIB with an identity of 98.6%. The phylogenetic trees constructed based on the complete ORF sequence or the 168-nt VP1/2A junction sequence and comparative analysis with reported HAV isolates suggested the presence of three distinct clusters within IIIA represented by HA-JNG04-90F, HA-JNG08-92F, and HAJ95-8F. The extreme 5' end sequences of IIIA and IIIB were well-conserved, beginning with the sequence UUCAAGAGGG. A single base deletion of G at nt 20, which is involved in the formation of a small loop in domain I, was characteristic of both IIIA and IIIB. Conserved and divergent amino acid sequences as well as amino acids unique to genotype III, IIIA or IIIB were recognized.

Identification of hepatitis A virus mimotopes by phage display, antigenicity and immunogenicity

A phage-displayed peptide approach was used to identify ligands mimicking antigenic determinants of hepatitis A virus (HAV) for the first time. Bacteriophages displaying HAV mimotopes were isolated from a phage-display peptide library by affinity selection on serum antibodies from hepatitis A patients. Selected phage-peptides were screened for reactivity with sera from HAV infected patients and healthy controls. Four cloned peptides with different sequences were identified as mimotopes of HAV; three of them showed similarity in their amino acid sequences with at least one of the VP3 and VP1 antigenic proteins of HAV. One clone was recognised by 92% of the positive sera. The phagotopes competed effectively with HAV for absorption of anti-HAV-specific antibodies in human sera, as determined by ELISA. The four phage clones induced neutralising anti-HAV antibodies in immunised mice. These results demonstrate the potential of this method to elucidate the disease related epitopes of HAV and to use these mimotopes in diagnostic applications or in the development of a mimotope-based hepatitis A vaccine without the necessity of manipulation of the virus.

Development, evaluation, and standardization of a real-time TaqMan reverse transcription-PCR assay for quantification of hepatitis A virus in clinical and shellfish samples

A standardized real-time reverse transcription-PCR (RT-PCR) assay has been developed for an accurate estimation of the number of genome copies of hepatitis A virus (HAV) in clinical and shellfish samples. Real-time procedures were based on the amplification of a fragment of the highly conserved 5' noncoding region and detection through an internal fluorescent probe, including TaqMan and beacon chemistries, in one- and two-step RT-PCR formats. The best performance in terms of sensitivity and reproducibility was achieved by a one-step TaqMan RT-PCR, with a sensitivity enabling the detection of 0.05 infectious unit and 10 copies of a single-stranded RNA (ssRNA) synthetic transcript. Standard reagents, such as a mengovirus strain and an ssRNA transcript, were employed as controls of nucleic acid extraction and RT-PCR, respectively. The test proved to be highly specific after a broad panel of enteric viruses was tested. Sequence alignment of target regions of the primers and probe proved them to be adequate for the quantification of all HAV genotypes. In addition, a quasispecies analysis of the mutant spectrum indicated that these regions are not prone to variability, thus confirming their robustness.

Influence of load of hepatitis A virus on disease severity and its relationship with clinical manifestations in patients with hepatitis A

BACKGROUND AND AIM

The purpose of the present study was to investigate the influence of viral load on disease severity and analyze the possible relationship of the load of hepatitis A virus (HAV) with disease severity and laboratory findings.

METHODS

Fifty-eight patients diagnosed with acute hepatitis A were used in the current study, of whom 12 patients progressed to severe acute hepatitis (s-AH) defined on the basis of a prothrombin time (PT) of <40% and 46 patients were diagnosed as having mild acute hepatitis (m-AH). The load of HAV was measured with real-time polymerase chain reaction.

RESULTS

Peak viral load showed a significant correlation with alanine aminotransferase (ALT) (r = 0.363, P = 0.0048) and PT levels (r = -0.330, P = 0.0110). In terms of disease severity, there was a significant correlation with ALT (r = 0.462, P = 0.0012) and PT levels (r = 0.400, P = 0.0059) in the m-AH group, but not in the s-AH group. A significant positive correlation of peak viral load with the C-reactive protein level (r = 0.270, P = 0.0400) and a significant negative correlation of peak viral load with the platelet count (r = -0.313, P = 0.0015) was also found.

CONCLUSIONS

The load of HAV was closely correlated with liver damage and disease severity in m-AH, but not in s-AH. The load of HAV was also closely associated with the increase in C-reactive protein level and enhancement of thrombocytopenia.

Capsid region involved in hepatitis A virus binding to glycophorin A of the erythrocyte membrane

Hepatitis A virus (HAV) has previously been reported to agglutinate human red blood cells at acidic pHs. Treatment of erythrocytes with different enzymes and chemical reagents indicated that HAV attachment is mediated through an interaction with sialylglycoproteins. HAV hemagglutination could be blocked by incubating the virus with glycophorin A, indicating that this sialylglycoprotein is the erythrocyte receptor. The number of receptors used was estimated to be around 500 per cell. At the same time, HAV-induced hemagglutination could also be blocked by either monoclonal antibody H7C27 or an anti-VP3(102-121) ascitic fluid, indicating that lysine 221 of VP1 and the surrounding VP3 residues lining the capsid pit are involved in HAV binding to erythrocytes.

The covalent coupling of HAV-VP3 (110-121) synthetic peptide to liposomes: physicochemical studies

In this work we have studied the conjugation of the immunogenic peptide sequence (110-121) belonging to the VP3 capsid protein of hepatitis A virus to the surface of preformed liposomes by means of an amide bond between the vesicles and the synthetic peptide. The surface activity of the conjugate at air/water interface was determined. Moreover, the interaction of the conjugate with lipids was also studied recording the pressure increases produced after the injection of the liposome-peptide preparation under dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG) and stearylamine (SA) monolayers at different initial surface pressures. As expected, due to the negative net charge of the liposome-peptide complex, the higher interaction was found with positive charge monolayers (SA). However, the conjugate was also able to incorporate to zwitterionic and anionic lipids. This behaviour was also confirmed performing compression isotherms of monolayers of these lipids spread on subphases containing the conjugate. These results suggest that the coupling of VP3 (110-121) to liposomes does not influence its ability to interact with membrane lipids such as DPPC and DPPG. Then it can be assumed that its immunogenicity will be preserved or even increased after this modification. All these results are also useful in the preparation of liposome-based synthetic peptide vaccines.

Evidence for quasispecies distributions in the human hepatitis A virus genome

Nucleotide sequence analysis of multiple molecular clones of the hepatitis A virus (HAV), generated by reverse transcription-PCR of two capsid-coding regions, revealed a degree of heterogeneity compatible with a quasispecies structure in three clinical samples. Passage of plaque-purified reference strain HAV pHM175 43c in FRhK-4 cells documented the generation of a mutant distribution of HAV genomes. The mutant spectra showed mutation frequencies in the range of 1 x 10(-3) to 1 x 10(-4) substitutions per nucleotide, with a dominance of transition over transversion mutations. While in the VP3-coding region, nonsynonymous mutations were predominant; in the VP1-coding region they were uncommon. Around 50% of the amino acid replacements involved residues located at or near antigenic sites. Most of the detected mutations occurred at or in the vicinity of rare codons, suggesting a dynamics of mutation-selection, predominantly at and around rare codons. The results indicate that despite antigenic conservation, HAV replicates as a complex distribution of mutants, a feature of viral quasispecies.

Liposome entrapment and immunogenic studies of a synthetic lipophilic multiple antigenic peptide bearing VP1 and VP3 domains of the hepatitis A virus: a robust method for vaccine design

Multiple antigen peptides (MAP) have been demonstrated to be efficient immunological reagents for the induction of immune responses to a variety of infectious agents. Several peptide domains of the hepatitis A virus (HAV) capsid proteins, mainly VP1 and VP3, are the immunodominant targets for a protective antibody response. In the present study we analyse the immunogenic properties of a tetrameric heterogeneous palmitoyl-derivatised MAP containing two defined HAV peptide sequences, VP1(11-25) and VP3(102-121), in rabbits immunised with either Freund's adjuvant or multilamellar liposomes. The immune response was evaluated with a specific enzyme immunoassay using MAP[VP1+VP3], VP1 and VP3 as targets. The avidity of the immune response was measured by a non-competitive enzyme-linked immunosorbent assay and by the surface plasmon resonance technology. Antisera raised against the lipo-MAP peptide entrapped in liposomes demonstrated high avidity of binding with affinity rate constants approximately one order of magnitude greater than those obtained with the Freund's protocol.

Capsid functions of inactivated human picornaviruses and feline calicivirus

The exceptional stability of enteric viruses probably resides in their capsids. The capsid functions of inactivated human picornaviruses and feline calicivirus (FCV) were determined. Viruses were inactivated by UV, hypochlorite, high temperature (72 degrees C), and physiological temperature (37 degrees C), all of which are pertinent to transmission via food and water. Poliovirus (PV) and hepatitis A virus (HAV) are transmissible via water and food, and FCV is the best available surrogate for the Norwalk-like viruses, which are leading causes of food-borne and waterborne disease in the United States. The capsids of all 37 degrees C-inactivated viruses still protected the viral RNA against RNase, even in the presence of proteinase K, which contrasted with findings with viruses inactivated at 72 degrees C. The loss of ability of the virus to attach to homologous cell receptors was universal, regardless of virus type and inactivation method, except for UV-inactivated HAV, and so virus inactivation was almost always accompanied by the loss of virus attachment. Inactivated HAV and FCV were captured by homologous antibodies. However, inactivated PV type 1 (PV-1) was not captured by homologous antibody and 37 degrees C-inactivated PV-1 was only partially captured. The epitopes on the capsids of HAV and FCV are evidently discrete from the receptor attachment sites, unlike those of PV-1. These findings indicate that the primary target of UV, hypochlorite, and 72 degrees C inactivation is the capsid and that the target of thermal inactivation (37 degrees C versus 72 degrees C) is temperature dependent.

Molecular characterization of hepatitis a virus isolates from a transcontinental shellfish-borne outbreak

One hundred eighty-four serologically confirmed cases of hepatitis A were reported in eastern Spain in 1999. A matched case-control study implicated imported coquina clams complying with European Union shellfish standards as the source of infection; this implication was confirmed by the detection by reverse transcription-PCR of hepatitis A virus (HAV) RNA in shellfish samples. In spite of the recognized low variability of HAV, genetic characterization of the complete capsid region of virus isolates from patient serum samples revealed the existence of both synonymous and nonsynonymous variants. Two antigenic variants were detected, one in a discontinuous epitope defined by monoclonal antibody K3-4C8 and a second in a linear VP1 epitope of the virus. In spite of these antigenic variants, all isolates were assigned to genotype IB, providing further evidence that the outbreak originated from a common source, although multiple strains were likely to be involved.

Mapping of linear epitopes on the capsid proteins of swine vesicular disease virus using monoclonal antibodies

The antigenic linear map of swine vesicular disease virus (SVDV) has been studied using a repertoire of monoclonal antibodies (mAbs) raised against a recombinant SVDV polyprotein, P1. Peptide-scanning analyses, cross-reactivity studies with homologous and heterologous viruses and predicted location on a computer-generated three-dimensional model of the capsid proteins have allowed the identification of five main linear sites. Two sites, the N terminus of VP3 and amino acids 51-60 on VP1, correspond to internal areas, conserved not only between SVDV isolates but also in the related enterovirus coxsackievirus B5. In contrast, three other regions, amino acids 142-161 of VP2, 61-70 of VP3 and the C terminus of VP1, are exposed on the external face of the capsid and subjected to antigenic variation, even among different SVDV isolates. Further minor sites that were antigenically conserved were identified on VP4. In contrast with conformational sites described previously, none of the linear epitopes identified in this work is involved in neutralization of virus infectivity and post-infection swine sera did not inhibit the binding of mAbs with the relevant epitopes. Both of these observations suggest that linear epitopes are poorly immunogenic in pigs. The characterization of linear sites has contributed to a better understanding of the antigenic structure of SVDV and mAbs used to this purpose may provide a useful tool for the improvement of diagnostic methods, such as antigen detection systems, and analyses of the antigenic profile of SVDV isolates.

Membrane fusion induced by a lipopeptidic epitope from VP3 capside protein of hepatitis A virus

Palmitoyl-VP3(110--121) (PVP3) is a synthetic lipopeptide derivative of a continuous epitope from the VP3 capsid protein of hepatitis A virus, and it is highly immunogenic in vivo. We have investigated the interaction of PVP3 with lipid model membranes of varying surface charge. Binding of PVP3 to anionic vesicles of PC/SM/PE/PS; (PC) 1-palmitoyl-2-oleoyl-phosphatidylcholine, (SM) sphingomyelin, (PE) 1,2-dipalmitoyl-phosphatidylethanolamine and (PS) L-alpha-phosphatidyl-L-serine, a composition that mimics the lipid component of natural membranes, was determined by tryptophan fluorescence and quenching experiments. In addition, and given the anionic net charge of the lipopeptide, binding to zwitterionic (PC/SM/PE) and cationic PC/SM/PE/DOTAP (DOTAP) 1,2-dioleoyl-3-trimethylammonium-propane mixtures was also determined. PVP3 binds to all three types of vesicles, but it adopts different forms depending on the electrical charge of the interface. This conclusion is supported by the insertion of PVP3 into lipid monolayers of the same charges spread at the air-water interface. The bound lipopeptide has membrane-destabilizing effects in all three vesicle compositions, as demonstrated by leakage of vesicle contents, whereas lipid mixing only occurs in cationic liposomes. Our results provide useful information for the design of a liposomal system that promotes a direct delivery of the membrane-incorporated immunogen to the immunocompetent cells, potentially increasing the immune response from the host.

Differences in secondary structure of HAV-synthetic peptides induced by the sequential order of T- and B-cell epitopes

The present study was undertaken to examine the structural features of two peptide constructs designed on the basis of linear combination of B and T-cell epitopes in different orientations (BT and TB) that may be important to explain the differences in the elicited antihepatitis A virus immune response and in the interaction with biological model membranes. A CD study was carried out and the corresponding quantitative analysis of the experimental data was done using deconvolution computer programs. Moreover, fluorescence experiments were performed to analyze differences in the fluorescence emission spectra of both molecules. The main conformational difference by CD studies was obtained working in aqueous medium. Although the TB sequence adopted a preferably random coil structure, the BT peptide was best fitted with beta-type structures. These results are further supported by fluorescence studies. These findings have relevance for the design of synthetic immunopeptides.

Membrane fusion by an RGD-containing sequence from the core protein VP3 of hepatitis A virus and the RGA-analogue: implications for viral infection

The interaction of an RGD-containing epitope from the hepatitis A virus VP3 capsid protein and its RGA-analogue with lipid membranes was studied by biophysical methods. Two types of model membrane were used: vesicles and monolayers spread at the air/water interface, with a composition that closely resembles the lipid moiety of hepatocyte membranes: PC/SM/PE/PC (40:33:12:15; PC: 1-palmitoyl-2-oleoylglycero-sn-3-phosphocholine; SM: sphingomyelin from chicken egg yolk; PE, 1,2-dipalmitoyl-phosphatidylethanolamine; PS: L-alpha-phosphatidyl-L-serine from bovine brain). In addition, zwitterionic PC/SM/PE (47:39:14) and cationic PC/SM/PE/DOTAP (40:33:12:15; DOTAP: 1,2-dioleoyl-3-trimethylammonium-propane) membranes were also prepared in order to dissect the electrostatic and hydrophobic components in the interaction. Changes in tryptophan fluorescence, acrylamide quenching, and resonance energy transfer experiments in the presence of vesicles, as well as the kinetics of insertion in monolayers, indicate that both peptides bind to the three types of membrane at neutral and acidic pH; however, binding is irreversible only at low pH. Membrane-destabilizing and fusogenic activities are triggered by acidification at pH 4-6, characteristic of the endosome. Fluorescence experiments show that VP3-RGD and VP3-RGA induce mixing of lipids and leakage or mixing of aqueous contents in anionic and cationic vesicles at pH 4-6, indicating leaky fusion. Interaction with zwitterionic vesicles (PC/SM/PE) results in leakage without lipid mixing, indicating pore formation. Replacement of aspartic acid in the RGD motif by alanine maintains the membrane-destabilizing properties of the peptide at low pH, but not its antigenicity. Since the RGD tripeptide is related to receptor-mediated cell adhesion and antigenicity, results suggest that receptor binding is not a molecular requirement for fusion. The possible involvement of peptide-induced membrane destabilization in the mechanism of hepatitis A virus infection of hepatocytes by the endosomal route is discussed.

Effect of chain length of HAV-VP3 synthetic peptides on its interaction with biomembrane models

Shorter analogues of a continuous epitope of hepatitis A virus, VP3(110-121) peptide, failed to react with convalescent sera, indicating the importance of the entire peptide in the epitope structure. To better understand the influence of the structural properties of this 12-mer peptide epitope on its biological activity, the interaction of smaller peptide analogues with phospholipid biomembrane models was investigated by a combination of spectroscopic and biophysical techniques. In this article we describe our findings concerning the surface activity and the interaction of peptides with simple mono- and bilayer membranes composed of a zwitterionic phospholipid (dipalmitoyl phosphatidylcholine, DPPC), an anionic phospholipid (dipalmitoyl phosphatidylglicerol, DPPG), or a DPPC/DPPG mixture. The results indicate that the net negative charge of the peptide is in some way responsible of the specific interactions between VP3(110-121) and membrane phospholipids, and necessary to induce beta-type conformations upon vesicle interaction.

Fluorescence study on the interaction of a multiple antigenic peptide from hepatitis A virus with lipid vesicles

The interaction of the multiple antigenic peptide MAP4VP3 with lipid membranes has been studied by spectroscopic techniques. MAP4VP3 is a multimeric peptide that corresponds to four units of the sequence 110-121 of the capsid protein VP3 of hepatitis A virus. In order to evaluate the electrostatic and hydrophobic components on the lipid-peptide interaction, small unilamelar vesicles of different compositions, including zwitterionic dipalmitoylphosphatidylcholine (DPPC), anionic dipalmitoylphosphatidylcholine/phatidylinositol (DPPC:PI 9:1), and cationic dipalmitoylphosphatidylcholine/stearylamine (DPPC:SA 9.5:0.5), were used as membrane models. Intrinsic tryptophan fluorescence changes and energy transfer experiments show that MAP4VP3 binds to all three types of vesicles with the same stoichiometry, indicating that the electrostatic component of the interaction is not important for binding of this anionic peptide. Steady-state polarization experiments with vesicles labeled with 1,6-diphenyl-1,3,5-hexatriene or with 1-anilino-8-naphtalene sulphonic acid indicate that MAP4VP3 induces a change in the packing of the bilayers, with a decrease in the fluidity of the lipids and an increase in the temperature of phase transition in all the vesicles. The percentage of lipid exposed to the bulk aqueous phase is around 60% in intact vesicles, and it does not change upon binding of MAP4VP3 to DPPC vesicles, indicating that the peptide does not alter the permeability of the membrane. An increase in the amount of lipid exposed to the aqueous phase in cationic vesicles indicates either lipid flip-flop or disruption of the vesicles. Binding to DPPC vesicles occurs without leakage of entrapped carboxyfluorescein, even at high mol fractions of peptide. However, a time-dependent leakage is seen with cationic DPPC/SA and anionic DPPC/PI vesicles, indicating that the peptide induces membrane destabilization and not lipid flip-flop. Resonance energy transfer experiments show that MAP4VP3 leakage from cationic vesicles is due to membrane fusion, whereas leakage from anionic vesicles is not accompanied by lipid mixing. Results show that MAP4VP3 interacts strongly with the lipid components of the membrane, and although binding is not of electrostatic nature, the bound form of the peptide has different activity depending on the membrane net charge; thus, it is membrane disruptive in cationic and anionic vesicles, whereas no destabilizing effect is seen in DPPC vesicles.

Use of linear and multiple antigenic peptides in the immunodiagnosis of acute hepatitis A virus infection

The reactivities of two panels of anti-HAV human sera from geographically distinct areas (Chile and Spain) to synthetic peptides from the VP1, VP2 and VP3 hepatitis A virus capsid proteins were examined by an enzyme-linked immunosorbent assay (ELISA) procedure. Two and four branched multiple antigenic peptides (MAPs) and palmitoylated peptides were compared with free synthetic sequences for the detection of IgM anti-HAV antibodies in the two panels of human sera. Our results showed that acute hepatitis A patient sera recognized preferentially homogeneous two branched MAPs and palmitic acid conjugated peptides. The palmitoyl-derived VP3(110-121) peptide and the corresponding dimeric MAP were the most sensitive and appropriate for serological studies of HAV-infected patients by ELISA, sensitivity and specificity being higher than 90% and 95%, respectively. These peptide-based tests open up new avenues in the development of peptide-based immunosorbent assays for the detection of acute HAV disease.

Liposomes as vehicles for the presentation of a synthetic peptide containing an epitope of hepatitis A virus

Previous work from our group showed that the entrapment of HAV-related synthetic peptides into multilamellar liposomes yielded satisfactory immunoresponses when administered to mice. In the present work we report investigative results for several liposome formulations of a 20-mer peptide related to VP3 capsid protein of HAV. In this sense, the recently introduced surface plasmon resonance technique has been applied to compare the different strategies of association between the synthetic peptide and phospholipid vesicles and to demonstrate that no significant alteration in antigenicity is produced when the peptide sequence is covalently coupled to the surface of small unilamellar vesicles. In addition, conformational data obtained by the circular dichroism technique have shown a decrease in the helical contribution of peptide-once linked to phospholipid; probably this change is due to the restriction introduced at the N-terminus of the sequence when coupled to the derivatized phospholipids at the surface of vesicle bilayers.

Antigenic epitopes of the hepatitis A virus polyprotein

Forty-two antigenic domains were identified across the hepatitis A virus (HAV) polyprotein by using a set of 237 overlapping 20-mer synthetic peptides spanning the entire HAV polyprotein and a panel of serum samples from acutely HAV-infected patients. The term "antigenic domain" is used in this study to define a protein region spanned with consecutive overlapping immunoreactive peptides. Nineteen antigenic domains were found within the structural proteins, and 22 were found within the nonstructural proteins, with 1 domain spanning the junction of VP1 and P2A proteins. Five of these domains were considered immunodominant, as judged by both the breadth and the strength of their immunoreactivity. One domain is located within the VP2 protein at position 57-90 aa. A second domain, located at position 767-842 aa, contains the C-terminal part of the VP1 protein and the entire P2A protein. A third domain, located at position 1403-1456 aa, comprises the C-terminal part of the P2C protein and the N-terminal half of the P3A protein. The fourth domain, located at position 1500-1519 aa, includes almost the entire P3B, and the last domain, located at position 1719-1764 aa, contains the C-terminal region of the P3C protein and the N-terminal region of the P3D protein. It is interesting to note that four of the five most immunoreactive domains are derived from small HAV proteins and/or encompass protein cleavage sites separating different HAV proteins. The HAV-specific immunoreactivity of each antigenically reactive peptide was confirmed by using seven HAV seroconversion panels. Collectively, these data demonstrate that HAV structural and nonstructural proteins contain antigenic epitopes that can be efficiently modeled with short synthetic peptides.

Interaction of VP3(110-121) Peptide with Hepatocyte and Erythrocyte Membrane Models

The use of synthetic peptides in the goal of developing a new, inexpensive vaccine against hepatitis A virus is one of the encouraging approaches followed by many laboratories. These peptides have to be well characterized, being their physicochemical properties one of the most relevant points to control. In that sense, one can consider the study of the peptide interaction with lipid monolayers by means of the Wilhelmy plate method, to gain insight into the possible mechanism of action at the membrane level. The peptide chosen corresponds to the lineal epitope of hepatitis A virus VP3(110-121). As far as the lipids used are concerned, they were selected according to the composition of hepatocytes and erythrocytes because these structures seem to play an important role in hepatitis proliferation and infection. The peptide was able to accommodate into lipid monolayers. Interaction was slightly lower in the hepatocyte model than in the erythrocyte model, probably due to the presence of cholesterol in the hepatocyte membrane. Copyright 1999 Academic Press.

Enhancement of the immunogenicity of a synthetic peptide bearing a VP3 epitope of hepatitis A virus

The immune responses elicited in mice by different forms of the VP3(110-121) B-epitope of the hepatitis A virus (HAV) were studied. Different forms of incorporation in liposomes were tested, encapsulation, rather than surface exposure, being the best antigenic preparation. Three larger peptides of the VP3 epitope, two of them containing a hepatitis B virus T-epitope, and a third containing a putative T-epitope of HAV (VP3(102-121)) were assayed. While this latter T-epitope induced an enhancement of the response against the VP3 B-epitope, the artificially coupled T-epitopes failed to induce a significant increase. The administration of two multiple antigenic peptide (MAP) constructs, the first containing the VP3(110-121) and VP1(11-25) HAV sequences and the second only the VP1(11-25) sequence, also suggested the presence of a T-epitope, since the response against the VP1 peptide was increased in the first construct.