HCVDB

Pathogen-driven cancers from a structural perspective: Targeting host-pathogen protein-protein interactions

Host-pathogen interactions (HPIs) affect and involve multiple mechanisms in both the pathogen and the host. Pathogen interactions disrupt homeostasis in host cells, with their toxins interfering with host mechanisms, resulting in infections, diseases, and disorders, extending from AIDS and COVID-19, to cancer. Studies of the three-dimensional (3D) structures of host-pathogen complexes aim to understand how pathogens interact with their hosts. They also aim to contribute to the development of rational therapeutics, as well as preventive measures. However, structural studies are fraught with challenges toward these aims. This review describes the state-of-the-art in protein-protein interactions (PPIs) between the host and pathogens from the structural standpoint. It discusses computational aspects of predicting these PPIs, including machine learning (ML) and artificial intelligence (AI)-driven, and overviews available computational methods and their challenges. It concludes with examples of how theoretical computational approaches can result in a therapeutic agent with a potential of being used in the clinics, as well as future directions.

Identification of drug resistance and immune-driven variations in hepatitis C virus (HCV) NS3/4A, NS5A and NS5B regions reveals a new approach toward personalized medicine

Cellular immune responses (T cell responses) during hepatitis C virus (HCV) infection are significant factors for determining the outcome of infection. HCV adapts to host immune responses by inducing mutations in its genome at specific sites that are important for HLA processing/presentation. Moreover, HCV also adapts to resist potential drugs that are used to restrict its replication, such as direct-acting antivirals (DAAs). Although DAAs have significantly reduced disease burden, resistance to these drugs is still a challenge for the treatment of HCV infection. Recently, drug resistance mutations (DRMs) observed in HCV proteins (NS3/4A, NS5A and NS5B) have heightened concern that the emergence of drug resistance may compromise the effectiveness of DAAs. Therefore, the NS3/4A, NS5A and NS5B drug resistance variations were investigated in this study, and their prevalence was examined in a large number of protein sequences from all HCV genotypes. Furthermore, potential CD4⁺ and CD8⁺ T cell epitopes were predicted and their overlap with genetic variations was explored. The findings revealed that many reported DRMs within NS3/4A, NS5A and NS5B are not drug-induced; rather, they are already present in HCV strains, as they were also detected in HCV-naïve patients. This study highlights several hot spots in which HLA and drug selective pressure overlap. Interestingly, these overlapping mutations were frequently observed among many HCV genotypes. This study implicates that knowledge of the host HLA type and HCV subtype/genotype can provide important information in defining personalized therapy.

Genetic Barrier to Direct Acting Antivirals in HCV Sequences Deposited in the European Databank

Background & Aims

Development of resistance results from mutations in the viral genome, and the presence of selective drug pressure leads to the emergence of a resistant virus population. The aim of this study was to analyze the impact of genetic variability on the genetic barrier to drug resistance to DAAs.

Methods

The genetic barrier was quantified based on the number and type of nucleotide mutations required to impart resistance, considering full-length HCV NS3, NS5A and NS5B regions segregated by genotype into subtypes 1a, 1b, 2a, 2b and 3a. This study analyzeds 789 NS3 sequences, 708 sequences and 536 NS5B sequences deposited in the European Hepatitis C Virus Database, in the following resistance-associated positions: NS3: F43/I/L/S/V, Q80K/R, R155K/G, A156G/S/T and D168A/C/E/G/H/N/T/V/Y; NS5A: L/M28A/T/V, Q30E/H/R, L31F/I/M/V, H58D or P58S and Y93C/F/H/N/S; NS5B: S282P/R/T, C316H/N/Y, S368T, Y448C/H, S556G/R, D559R.

Results

Variants that require only one transversion in NS3 were found in 4 positions and include F43S, R80K, R155K/G and A156T. The genetic barrier to resistance shows subtypic differences at position 155 of the NS3 gene where a single transition is necessary in subtype 1a. In the NS5A gene, 5 positions where only one nucleotide change can confer resistance were found, such as L31M which requires one transversion in all subtypes, except in 0.28% of 1b sequences; and R30H, generated by a single transition, which was found in 10.25% of the sequences of genotype 1b. Other subtypic differences were observed at position 58, where resistance is less likely in genotype 1a because a transversion is required to create the variant 58S. For the NS5B inhibitors, the genetic barrier at positions conferring resistance was nearly identical in subtypes 1a and 1b, and single transitions or transversions were necessary in 5 positions to generate a drug-resistant variant of HCV. The positions C316Y and S556D required only one transition in all genotypes, Y448H and S556 G/N/R positions required only one transition for up to 98.8% of the sequences analyzed. A single variant in position 448 in genotype 1a is less likely to become the resistance variant 448H because it requires two transversions. Also, in the position 559D a transversion and a transition were necessary to generate the resistance mutant D559H.

Conclusion

Results revealed that in 14 out of 16 positions, conversion to a drug-resistant variant of HCV required only one single nucleotide substitutions threatening direct acting antivirals from all three classes.

Bridging basic science and clinical research: the EASL Monothematic Conference on Translational Research in Viral Hepatitis

The EASL Monothematic Conference on Translational Research in Viral Hepatitis brought together a group of leading scientists and clinicians working on both, basic and clinical aspects of viral hepatitis, thereby building bridges from bench to bedside. This report recapitulates the presentations and discussions at the conference held in Lyon, France on November 29-30, 2013. In recent years, great advances have been made in the field of viral hepatitis, particularly in hepatitis C virus (HCV) infection. The identification of IL28B genetic polymorphisms as a major determinant for spontaneous and treatment-induced HCV clearance was a seminal discovery. Currently, hepatologists are at the doorstep of even greater advances, with the advent of a wealth of directly acting antivirals (DAAs) against HCV. Indeed, promising results have accumulated over the last months and few years, showing sustained virological response (SVR) rates of up to 100% with interferon-free DAA combination therapies. Thus, less than 25 years after its identification, HCV infection may soon be curable in the vast majority of patients, highlighting the great success of HCV research over the last decades. However, viral hepatitis and its clinical complications such as liver cirrhosis and hepatocellular carcinoma (HCC) remain major global challenges. New therapeutic strategies to tackle hepatitis B virus (HBV) and hepatitis D virus (HDV) infection are needed, as current therapies have undeniable limitations. Nucleoside/nucleotide analogues (NUC) can efficiently control HBV replication and reduce or even reverse liver damage. However, these drugs have to be given for indefinite periods in most patients to maintain virological and biochemical responses. Although sustained responses off treatment can be achieved by treatment with (pegylated) interferon-α, only about 10-30% of patients effectively resolve chronic hepatitis B. It was the goal of this conference to review the progress made over the last years in chronic viral hepatitis research and to identify key questions that need to be addressed in order to close the gap between basic and clinical research and to develop novel preventive and treatment approaches for this most common cause of liver cirrhosis and HCC.

A novel assay for detection of hepatitis C virus-specific effector CD4(+) T cells via co-expression of CD25 and CD134

Hepatitis C virus (HCV)-specific CD4(+) effector T cell responses are likely to play a key role in the immunopathogenesis of HCV infection by promoting viral clearance and maintaining control of viraemia. As the precursor frequency of HCV-specific CD4(+) T cells in peripheral blood is low, favoured assay systems such as intracellular cytokine (ICC) or tetramer staining have limited utility for ex vivo analyses. Accordingly, the traditional lymphocyte proliferation assay (LPA) remains the gold standard, despite detecting responses in only a minority of infected subjects. Recently, we reported development and validation of a novel whole blood CD4(+) effector T cell assay based on ex vivo antigen stimulation followed by co-expression of CD25 and CD134 on CD4(+) T cells. Here we report adaptation of this assay to assessment of HCV-specific responses in cryopreserved peripheral blood mononuclear cells using standardised antigens, including peptide pools, viral supernatants and recombinant viral proteins. The assay allowed detection of HCV-specific CD4 responses in donors with both resolved and chronic infection. Responses were highly correlated with those revealed by LPA. Application of this assay will further define the role of CD4(+) T cells in the immunopathogenesis of HCV infection.

Contribution of genome-wide HCV genetic differences to outcome of interferon-based therapy in Caucasian American and African American patients

BACKGROUND

Hepatitis C virus (HCV) has six major genotypes, and patients infected with genotype 1 respond less well to interferon-based therapy than other genotypes. African American patients respond to interferon alpha-based therapy at about half the rate of Caucasian Americans. The effect of HCV's genetic variation on treatment outcome in both racial groups is poorly understood.

METHODOLOGY

We determined the near full-length pre-therapy consensus sequences from 94 patients infected with HCV genotype 1a or 1b undergoing treatment with peginterferon alpha-2a and ribavirin through the Virahep-C study. The sequences were stratified by genotype, race and treatment outcome to identify HCV genetic differences associated with treatment efficacy.

PRINCIPAL FINDINGS

HCV sequences from patients who achieved sustained viral response were more diverse than sequences from non-responders. These inter-patient diversity differences were found primarily in the NS5A gene in genotype 1a and in core and NS2 in genotype 1b. These differences could not be explained by host selection pressures. Genotype 1b but not 1a African American patients had viral genetic differences that correlated with treatment outcome.

CONCLUSIONS & SIGNIFICANCE

Higher inter-patient viral genetic diversity correlated with successful treatment, implying that there are HCV genotype 1 strains with intrinsic differences in sensitivity to therapy. Core, NS3 and NS5A have interferon-suppressive activities detectable through in vitro assays, and hence these activities also appear to function in human patients. Both preferential infection with relatively resistant HCV variants and host-specific factors appear to contribute to the unusually poor response to therapy in African American patients.

Characterization of the cellular immune response in hepatitis C virus infection

Hepatitis C virus (HCV), a hepatotropic RNA virus, is a major causative agent of chronic hepatitis, liver cirrhosis, and hepatocellular carcinomas. The host immune responses, especially cellular immune responses, play an important role in viral clearance, liver injury, and persistent HCV infection. A thorough characterization of the HCV cellular immune responses is important for understanding the interplays between host immune system and viral components, as well as for developing effective therapeutic and prophylactic HCV vaccines. Recent advances that provide better understanding the cell immune responses in HCV infection are summarized in this article.

ORION-VIRCAT: a tool for mapping ICTV and NCBI taxonomies

Viruses, viroids and prions are the smallest infectious biological entities that depend on their host for replication. The number of pathogenic viruses is considerably large and their impact in human global health is well documented. Currently, the International Committee on the Taxonomy of Viruses (ICTV) has classified approximately 4379 virus species while the National Center for Biotechnology Information Viral Genomes Resource (NCBI-VGR) database has mapped 617 705 proteins to eight large taxonomic groups. Despite these efforts, an automated approach for mapping the ICTV master list and its officially accepted virus naming to the NCBI-VGR's taxonomical classification is not available. Due to metagenomic sequencing, it is likely that the discovery and naming of new viral species will increase by at least ten fold. Unfortunately, existing viral databases are not adequately prepared to scale, maintain and annotate automatically ultra-high throughput sequences and place this information into specific taxonomic categories. ORION-VIRCAT is a scalable and interoperable object-relational database designed to serve as a resource for the integration and verification of taxonomical classifications generated by the ICTV and NCBI-VGR. The current release (v1.0) of ORION-VIRCAT is implemented in PostgreSQL and it has been extended to ORACLE, MySQL and SyBase. ORION-VIRCAT automatically mapped and joined 617 705 entries from the NCBI-VGR to the viral naming of the ICTV. This detailed analysis revealed that 399 095 entries from the NCBI-VGR can be mapped to the ICTV classification and that one Order, 10 families, 35 genera and 503 species listed in the ICTV disagree with the the NCBI-VGR classification schema. Nevertheless, we were eable to correct several discrepancies mapping 234 000 additional entries.Database URL:http://www.orionbiosciences.com/research/orion-vircat.html.

HCV genotyping using statistical classification approach

The genotype of Hepatitis C Virus (HCV) strains is an important determinant of the severity and aggressiveness of liver infection as well as patient response to antiviral therapy. Fast and accurate determination of viral genotype could provide direction in the clinical management of patients with chronic HCV infections. Using publicly available HCV nucleotide sequences, we built a global Position Weight Matrix (PWM) for the HCV genome. Based on the PWM, a set of genotype specific nucleotide sequence "signatures" were selected from the 5' NCR, CORE, E1, and NS5B regions of the HCV genome. We evaluated the predictive power of these signatures for predicting the most common HCV genotypes and subtypes. We observed that nucleotide sequence signatures selected from NS5B and E1 regions generally demonstrated stronger discriminant power in differentiating major HCV genotypes and subtypes than that from 5' NCR and CORE regions. Two discriminant methods were used to build predictive models. Through 10 fold cross validation, over 99% prediction accuracy was achieved using both support vector machine (SVM) and random forest based classification methods in a dataset of 1134 sequences for NS5B and 947 sequences for E1. Prediction accuracy for each genotype is also reported.

The major form of hepatitis C virus alternate reading frame protein is suppressed by core protein expression

Hepatitis C virus (HCV) is a human RNA virus encoding 10 proteins in a single open reading frame. In the +1 frame, an ‘alternate reading frame’ (ARF) overlaps with the core protein-encoding sequence and encodes the ARF protein (ARFP). Here, we investigated the molecular regulatory mechanisms of ARFP expression in HCV target cells. Chimeric HCV-luciferase reporter constructs derived from the infectious HCV prototype isolate H77 were transfected into hepatocyte-derived cell lines. Translation initiation was most efficient at the internal AUG codon at position 86/88, resulting in the synthesis of a truncated ARFP named _86/88ARFP. Interestingly, _86/88ARFP synthesis was markedly enhanced in constructs containing an inactivated core protein reading frame. This enhancement was reversed by co-expression of core protein in trans, demonstrating suppression of ARFP synthesis by HCV core protein. In conclusion, our results indicate that translation of ARFP occurs mainly by alternative internal initiation at position 86/88 and is regulated by HCV core protein expression. The suppression of ARFP translation by HCV core protein suggests that ARFP expression is inversely linked to the level of viral replication. These findings define key mechanisms regulating ARFP expression and set the stage for further studies addressing the function of ARFP within the viral life cycle.

Development and public release of a comprehensive hepatitis virus database

AIM

Currently, approximately 44 000 hepatitis C virus (HCV), 11 000 hepatitis B virus (HBV), and 1600 hepatitis E virus (HEV) sequences are available at the International Nucleotide Sequence Database Collaboration (INSDC, previously known as DDBJ/EMBL/GenBank), and the number of these virus sequences is growing rapidly. However, since INDSC is not specialized to hepatitis viruses, it is difficult to retrieve information of virological or clinical interests from it. Thus, it is quite worthwhile to construct a specialized database for the hepatitis virus sequences and to make it accessible to researchers worldwide.

METHODS

We developed a WWW-based database hepatitis virus database (HVDB), which contains all the HCV, HBV, and HEV sequences available at INSDC. In the HVDB, all piece sequences obtained from INSDC are arranged to the genomesequence of each virus. Also given in the database are the phylogenetic relationships of each locus on the genome among variants for each virus.

RESULTS

Users of the database can easily retrieve entries (sequences with annotations) of the specific genotype by referring to the phylogenetic relationships or those of specific loci by referring to the genome map information. HVDB provides users with a tool for phylogenetic analysis that can be used in combination with the data retrieval tools.

CONCLUSION

The latest release is publicly accessible at the HVDB website: http://s2as02.genes.nig.ac.jp.

Seven nucleotide changes characteristic of the hepatitis C virus genotype 3 5' untranslated region: correlation with reduced in vitro replication

Computer analysis of 158 hepatitis C virus (HCV) 5' untranslated region (5' UTR) sequences from the six genotypes showed that the 5' UTR from genotype 3 displays seven specific non-contiguous nucleotide changes, at positions 8, 13, 14, 70, 97, 203 and 224. The purpose of this study was to investigate the impact of these changes on translation and replication activities. Indeed, these modifications could alter both the internal ribosome entry site (IRES) present in the 5' UTR of the plus-strand RNA and the 3' end of the minus strand involved in the initiation of plus-strand RNA synthesis. We found that the genotype 3-specific nucleotide changes do not modify the in vitro or ex vivo translation activity of the corresponding IRES, in comparison with that of genotype 1. In contrast, in vitro replication from the minus-strand RNA is eight times less efficient for genotype 3 than for genotype 1 RNA, suggesting the involvement of some nucleotide changes in the reduction of RNA synthesis. Nucleotides 13, 14 and 224 were found to be responsible for this effect. Moreover, a reduced replicative activity was confirmed ex vivo for genotype 3, but to a lesser extent than that observed in vitro, using an RNA minigenome.

Characterization of fusion determinants points to the involvement of three discrete regions of both E1 and E2 glycoproteins in the membrane fusion process of hepatitis C virus

Infection of eukaryotic cells by enveloped viruses requires the merging of viral and cellular membranes. Highly specific viral surface glycoproteins, named fusion proteins, catalyze this reaction by overcoming inherent energy barriers. Hepatitis C virus (HCV) is an enveloped virus that belongs to the genus Hepacivirus of the family Flaviviridae. Little is known about the molecular events that mediate cell entry and membrane fusion for HCV, although significant progress has been made due to recent developments in infection assays. Here, using infectious HCV pseudoparticles (HCVpp), we investigated the molecular basis of HCV membrane fusion. By searching for classical features of fusion peptides through the alignment of sequences from various HCV genotypes, we identified six regions of HCV E1 and E2 glycoproteins that present such characteristics. We introduced conserved and nonconserved amino acid substitutions in these regions and analyzed the phenotype of HCVpp generated with mutant E1E2 glycoproteins. This was achieved by (i) quantifying the infectivity of the pseudoparticles, (ii) studying the incorporation of E1E2 and their capacity to mediate receptor binding, and (iii) determining their fusion capacity in cell-cell and liposome/HCVpp fusion assays. We propose that at least three of these regions (i.e., at positions 270 to 284, 416 to 430, and 600 to 620) play a role in the membrane fusion process. These regions may contribute to the merging of viral and cellular membranes either by interacting directly with lipid membranes or by assisting the fusion process through their involvement in the conformational changes of the E1E2 complex at low pH.

Hepatitis C Virus p7 membrane protein quasispecies variability in chronically infected patients treated with interferon and ribavirin, with or without amantadine

A clinical study was carried out to compare the response rate of two groups of non-responder (NR) hepatitis C virus (HCV) genotype 1 chronically infected patients treated with interferon and ribavirin, with or without amantadine. The viral load decreased more markedly in the group treated by tritherapy including amantadine, but the response rate at the end of treatment was not significantly different between bitherapy and tritherapy. As amantadine could have an antiviral effect on the ion channel activity of the p7 HCV protein, the p7 quasispecies was characterized by cloning and sequencing. Sequence data were analyzed to determine the pattern and significance of p7 genetic heterogeneity and a possible relationship with therapy. Subtype differences were confirmed between p7 HCV genotypes 1a and 1b, and quasispecies analysis showed a reduction of genetic diversity in subtype 1a, but not 1b, during tritherapy. However, the absence of changes at numerous positions, as well as the conservative changes at other positions, indicated the high conservation of the p7 structure. Residue His-17, proposed to interact with amantadine, was fully conserved in both subtypes 1a and 1b, independently of amantadine administration. In conclusion, although the analysis of the p7 sequences revealed a selective pressure during therapy, no specific residues appeared to be linked to the effect of amantadine on viral decline. These results suggest that the potential antiviral effect of amantadine might be non-specific and related to a reduction in endosomal acidification and therefore reduced viral entry of HCV via its pH-dependent pathway.

Genome Information Broker for Viruses (GIB-V): database for comparative analysis of virus genomes

Genome Information Broker for Viruses (GIB-V) is a comprehensive virus genome/segment database. We extracted 18 418 complete virus genomes/segments from the International Nucleotide Sequence Database Collaboration (INSDC, ) by DNA Data Bank of Japan (DDBJ), EMBL and GenBank and stored them in our system. The list of registered viruses is arranged hierarchically according to taxonomy. Keyword searches can be performed for genome/segment data or biological features of any virus stored in GIB-V. GIB-V is equipped with a BLAST search function, and search results are displayed graphically or in list form. Moreover, the BLAST results can be used online with the ClustalW feature of the DDBJ. All available virus genome/segment data can be collected by the GIB-V download function. GIB-V can be accessed at no charge at .

euHCVdb: the European hepatitis C virus database

The hepatitis C virus (HCV) genome shows remarkable sequence variability, leading to the classification of at least six major genotypes, numerous subtypes and a myriad of quasispecies within a given host. A database allowing researchers to investigate the genetic and structural variability of all available HCV sequences is an essential tool for studies on the molecular virology and pathogenesis of hepatitis C as well as drug design and vaccine development. We describe here the European Hepatitis C Virus Database (euHCVdb, ), a collection of computer-annotated sequences based on reference genomes. The annotations include genome mapping of sequences, use of recommended nomenclature, subtyping as well as three-dimensional (3D) molecular models of proteins. A WWW interface has been developed to facilitate database searches and the export of data for sequence and structure analyses. As part of an international collaborative effort with the US and Japanese databases, the European HCV Database (euHCVdb) is mainly dedicated to HCV protein sequences, 3D structures and functional analyses.

Phylogenetic analysis of previously nontypeable hepatitis C virus isolates from Argentina

Phylogenetic analysis of hepatitis C virus isolates from Argentina that were previously nontypeable by restriction fragment length polymorphism (RFLP) analysis revealed that they belong to genotype 1a. A substitution at position 107 (G-->A), which is the landmark of these strains, was shown to be distributed among isolates worldwide. The RFLP patterns obtained for these isolates should be added to the ones reported for genotype 1 isolates.

Structural determinants that target the hepatitis C virus core protein to lipid droplets

Hepatitis C virus core protein is targeted to lipid droplets, which serve as intracellular storage organelles, by its C-terminal domain, termed D2. From circular dichroism and nuclear magnetic resonance analyses, we demonstrate that the major structural elements within D2 consist of two amphipathic alpha-helices (Helix I and Helix II) separated by a hydrophobic loop. Both helices require a hydrophobic environment for folding, indicating that lipid interactions contribute to their structural integrity. Mutational studies revealed that a combination of Helix I, the hydrophobic loop, and Helix II is essential for efficient lipid droplet association and pointed to an in-plane membrane interaction of the two helices at the phospholipid layer interface. Aside from lipid droplet association, membrane interaction of D2 is necessary for folding and stability of core following maturation at the endoplasmic reticulum membrane by signal peptide peptidase. These studies identify critical determinants within a targeting domain that enable trafficking and attachment of a viral protein to lipid droplets. They also serve as a unique model for elucidating the specificity of protein-lipid interactions between two membrane-bound organelles.

Hepatitis C databases, principles and utility to researchers

Part of the effort to develop hepatitis C-specific drugs a nd vaccines is the study of genetic variability of allpublicly available HCV sequences. Three HCV databases are currently available to aid this effort and to provide additional insight into the basic biology, immunology, and evolution of the virus. The Japanese HCV database (http://s2as02.genes.nig.ac.jp) gives access to a genomic mapping of sequences as well as their phylogenetic relationships. The European HCV database (http://euhcvdb.ibcp.fr) offers access to a computer-annotated set of sequences and molecular models of HCV proteins and focuses on protein sequence, structure and function analysis. The HCV database at the Los Alamos National Laboratory in the United States (http://hcv.lanl.gov) provides access to a manually annotated sequence database and a database of immunological epitopes which contains concise descriptions of experimental results. In this paper, we briefly describe each of these databases and their associated websites and tools, and give some examples of their use in furthering HCV research.

Basic residues in hypervariable region 1 of hepatitis C virus envelope glycoprotein e2 contribute to virus entry

The N terminus of hepatitis C virus (HCV) envelope glycoprotein E2 contains a hypervariable region (HVR1) which has been proposed to play a role in viral entry. Despite strong amino acid variability, HVR1 is globally basic, with basic residues located at specific sequence positions. Here we show by analyzing a large number of HVR1 sequences that the frequency of basic residues at each position is genotype dependent. We also used retroviral pseudotyped particles (HCVpp) harboring genotype 1a envelope glycoproteins to study the role of HVR1 basic residues in entry. Interestingly, HCVpp infectivity globally increased with the number of basic residues in HVR1. However, a shift in position of some charged residues also modulated HCVpp infectivity. In the absence of basic residues, infectivity was reduced to the same level as that of a mutant deleted of HVR1. We also analyzed the effect of these mutations on interactions with some potential HCV receptors. Recognition of CD81 was not affected by changes in the number of charged residues, and we did not find a role for heparan sulfates in HCVpp entry. The involvement of the scavenger receptor class B type I (SR-BI) was indirectly analyzed by measuring the enhancement of infectivity of the mutants in the presence of the natural ligand of SR-BI, high-density lipoproteins (HDL). However, no correlation between the number of basic residues within HVR1 and HDL enhancement effect was observed. Despite the lack of evidence of the involvement of known potential receptors, our results demonstrate that the presence of basic residues in HVR1 facilitates virus entry.

Using maximum likelihood method to detect adaptive evolution of HCV envelope protein-coding genes

Nonsynonymous-synonymous substitution rate ratio (d N /d S ) is an important measure for evaluating selective pressure based on the protein-coding sequences. Maximum likelihood (ML) method with codon-substitution models is a powerful statistic tool for detecting amino acid sites under positive selection and adaptive evolution. We analyzed the hepatitis C virus (HCV) envelope protein-coding sequences from 18 general geno/subtypes worldwide, and found 4 amino acid sites under positive selection. Since these sites are located in different immune epitopes, it is reasonable to anticipate that our study would have potential values in biomedicine. It also suggests that the ML method is an effective way to detect adaptive evolution in virus proteins with relatively high genetic diversity.

Consensus proposals for a unified system of nomenclature of hepatitis C virus genotypes

International standardization and coordination of the nomenclature of variants of hepatitis C virus (HCV) is increasingly needed as more is discovered about the scale of HCV-related liver disease and important biological and antigenic differences that exist between variants. A group of scientists expert in the field of HCV genetic variability, and those involved in development of HCV sequence databases, the Hepatitis Virus Database (Japan), euHCVdb (France), and Los Alamos (United States), met to re-examine the status of HCV genotype nomenclature, resolve conflicting genotype or subtype names among described variants of HCV, and draw up revised criteria for the assignment of new genotypes as they are discovered in the future. A comprehensive listing of all currently classified variants of HCV incorporates a number of agreed genotype and subtype name re-assignments to create consistency in nomenclature. The paper also contains consensus proposals for the classification of new variants into genotypes and subtypes, which recognizes and incorporates new knowledge of HCV genetic diversity and epidemiology. A proposal was made that HCV variants be classified into 6 genotypes (representing the 6 genetic groups defined by phylogenetic analysis). Subtype name assignment will be either confirmed or provisional, depending on the availability of complete or partial nucleotide sequence data, or remain unassigned where fewer than 3 examples of a new subtype have been described. In conclusion, these proposals provide the framework by which the HCV databases store and provide access to data on HCV, which will internationally coordinate the assignment of new genotypes and subtypes in the future.

Hepatitis C virus core protein is a dimeric alpha-helical protein exhibiting membrane protein features

The building block of hepatitis C virus (HCV) nucleocapsid, the core protein, together with viral RNA, is composed of different domains involved in RNA binding and homo-oligomerization. The HCV core protein 1-169 (C(HCV)169) and its N-terminal region from positions 1 to 117 (C(HCV)117) were expressed in Escherichia coli and purified to homogeneity suitable for biochemical and biophysical characterizations. The overall conformation and the oligomeric properties of the resulting proteins C(HCV)169 and C(HCV)117 were investigated by using analytical centrifugation, circular dichroism, intrinsic fluorescence measurements, and limited proteolysis. Altogether, our results show that core protein (C(HCV)169) behaves as a membranous protein and forms heterogeneous soluble micelle-like aggregates of high molecular weight in the absence of detergent. In contrast, it behaves, in the presence of mild detergent, as a soluble, well-folded, noncovalent dimer. Similar to findings observed for core proteins of HCV-related flaviviruses, the HCV core protein is essentially composed of alpha-helices (50%). In contrast, C(HCV)117 is soluble and monodispersed in the absence of detergent but is unfolded. It appears that the folding of the highly basic domain from positions 2 to 117 (2-117 domain) depends on the presence of the 117-169 hydrophobic domain, which contains the structural determinants ensuring the binding of core with cellular membranes. Finally, our findings provide valuable information for further investigations on isolated core protein, as well as for attempts to reconstitute nucleocapsid particles in vitro.