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Hepatitis E virus (HEV) is the main cause of acute hepatitis worldwide. The viral infection caused by G1 HEV in pregnant women has become a major health concern in the past few years. The mechanism underlying the pathogenesis of viral infection in HEV G1 isolates is attributed to four different open-reading frames (ORFs) i.e., ORF1, ORF2, ORF3 and ORF4. The present analysis has considered ORF4 protein as the molecular target due to its intrinsic disorder propensity. Intrinsically disordered regions (IDRs) are regions in proteins that do not possess stable secondary and tertiary structure and are prevalent in eukaryotes. IDRs are found to be closely associated with numerous human diseases, for instance, Parkinson and Alzheimer disease. The extreme flexibility and random coiled conformations of IDR allow it to undergo protein-protein interaction (PPI). The 3-dimensional (3D) structures of the target protein were designed using homology modelling algorithms. The generated models were assessed through structure verification tool PROCHECK. In this paper, we provide an overview of ORF4 protein structure-function relationship and its involvement in several biological processes through PPIs. Our results suggest that ORF4 protein has the potential to act as drug molecule, thus can accelerate the process of drug designing strategies against HEV.

Hepatitis E virus (HEV) belongs to the family Hepeviridae and is the major cause of hepatitis E infections across the globe. Recently, a novel viral protein of HEV, named as open reading frame (ORF4), has been associated with its replication in genotype 1 isolates. However, much information regarding ORF4 has not been explored. Thus, the study was conceptualized to explore the structural and functional features of HEV ORF4 protein to better understand the possible molecular mechanisms. The detailed investigation of the ORF4 was carried out in terms of its physicochemical properties, secondary and tertiary structure predictions and functional analysis using different bioinformatics tools. The in silico analyses revealed that ORF4 sequences were enriched in Serine, Proline and Glycine amino acid residues suggesting the prevalence of disordered residues. The protein was found to be thermostable, unstable and highly hydrophobic. The structural analysis showed the presence of cleft, tunnel and pore suggesting their participation in interaction with other molecules. Moreover, identification of several modified sites in ORF4 sequences such as glycosylation, phosphorylation and myristoylation sequences suggest their involvement in cellular signaling pathways and biological processes. Thus, taken together, it can be interpreted that HEV ORF4 possesses significant enormous flexibility due to the presence of Serine, Glycine and Proline amino acids, which suggest its involvement in protein-protein interaction. Furthermore, the presence of motifs, clefts and tunnels also strengthens our analysis, suggesting the commitment of ORF4 towards interaction with other target molecules. Thus, it could be potent drug-targets.

Hepatitis E virus (HEV) is the cause of a liver disease hepatitis E. The translation product of HEV ORF2 has recently been demonstrated as a protein involved in multiple functions besides performing its major role of a viral capsid. As intrinsically disordered regions (IDRs) are linked to various essential roles in the virus's life cycle, we analyzed the disorder pattern distribution of the retrieved ORF2 protein sequences by employing different online predictors. Our findings might provide some clues on the disorder-based functions of ORF2 protein that possibly help us in understanding its behavior other than as a HEV capsid protein. The modeled three dimensional (3D) structures of ORF2 showed the predominance of random coils or unstructured regions in addition to major secondary structure components (alpha helix and beta strand). After initial scrutinization, the predictors VLXT and VSL2 predicted ORF2 as a highly disordered protein while the predictors VL3 and DISOPRED3 predicted ORF2 as a moderately disordered protein, thus categorizing HEV-ORF2 into IDP (intrinsically disordered protein) or IDPR (intrinsically disordered protein region) respectively. Thus, our initial predicted disorderness in ORF2 protein 3D structures was in excellent agreement with their predicted disorder distribution patterns (evaluated through different predictors). The abundance of MoRFs (disorder-based protein binding sites) in ORF2 was observed that signified their interaction with binding partners which might further assist in viral infection. As IDPs/IDPRs are targets of regulation, we carried out the phosphorylation analysis to reveal the presence of post-translationally modified sites. Prevalence of several disordered-based phosphorylation sites further signified the involvement of ORF2 in diverse and significant biological processes. Furthermore, ORF2 structure-associated functions revealed its involvement in several crucial functions and biological processes like binding and catalytic activities. The results predicted ORF2 as a protein with multiple functions besides its role as a capsid protein. Moreover, the occurrence of IDPR/IDP in ORF2 protein suggests that its disordered region might serve as novel drug targets via functioning as potential interacting domains. Our data collectively might provide significant implication in HEV vaccine search as disorderness in viral proteins is related to mechanisms involved in immune evasion.

Hepatitis E virus (HEV) is the chief cause of hepatitis E (inflammation of liver) across the globe. The Norway rat HEV genome consists of six open reading frames (ORFs), i.e., ORF1, ORF2, ORF3, ORF4, ORF5 and ORF5. The additional reading frame encoded protein ORF5 protein's structure and function remain to be explored. Therefore, the presented study was conceptualized to analyze the ORF5 protein for its physiochemical properties, primary structure, secondary structure, tertiary structure and functional characteristics using bioinformatics tools. The initial analysis revealed ORF5 protein as unstable, thermostable, hydrophilic and highly basic in nature. The primary structural analysis revealed higher percentages of amino acids Arg, Leu, Pro, Ser and Gly, which suggested that the ORF5 protein is richly endowed with some regulatory amino acids (Leu, Pro and Gly). The secondary structure of ORF5 protein showed all three major components (alpha-helix, beta-strand and random coil). The tertiary structure generated through homology modelling revealed mixed alpha/beta structural fold with subsequently higher percentage of strands and abundance of coils. Moreover, the surface analysis revealed the several clefts and tunnels along with few pores, clearly suggested the ability of ORF5 protein towards interaction with other molecules. The ORF5 protein was also identified with several post-translationally modified sites including glycosylation, phosphorylation and myriystoylation. The presence of these modified sites indicated the role of ORF5 protein in regulation. Thus, our analyses taken together interpret the ORF5 protein's essentiality in HEV. This data will help in exploring the prospective role of this additional genomic component of rat HEV through the sequence, structure and functional annotation of ORF5 protein.

Hepatitis E virus (HEV) of the family Hepeviridae, is a major causative agent of acute hepatitis in developing countries. The Norway rat HEV genome is organized into six open reading frames (ORFs), i.e., ORF1, ORF2, ORF3, ORF4, ORF5 and ORF6. The additional reading frame encoded protein ORF6 is attributed to life cycle of rat HEV. As ORF6 protein's remains to be explored in terms of its structural and functional implications, the following study was conceptualized to explore the prospective role of this additional genomic component of rat HEV. The detailed computational investigation was carried out for the ORF6 protein to elucidate its physiochemical properties, primary structure, secondary structure, tertiary structure and post-translational modifications, motif prediction and other functional characteristics. The in silico analysis revealed ORF6 protein as unstable, highly thermostable, hydrophobic and basic in nature. The amino acid compositional analysis revealed higher abundance of Leu, Arg, Ile and Pro amino acids in the polypeptide chain of ORF6 protein. The secondary structural analysis revealed all the three major elements, i.e., alpha-helices, beta-strands and coils. The generated 3D structural model of the ORF6 protein through homology modeling algorithm revealed mixed alpha/beta structural fold of the ORF6 protein with abundance of coils. Additionally, the structural models revealed the presence of clefts and a tunnel. The identified binding functions and the presence of several clefts suggested the commitment of ORF6 protein towards interaction with other ligand molecules. This theoretical study will facilitate towards deciphering the role of unexplored ORF6 encoded protein, thereby providing better understanding towards the pathogenesis of Norway rat HEVs.

Hepatitis E virus (HEV) is a quasi-enveloped RNA virus of the family Hepeviridae. HEV is the chief cause of acute hepatitis worldwide, causing approximately 20 million infections annually, which results in 60,000 deaths. Due to insufficiency in appropriate HEV in vitro cell culture systems, our knowledge of its pathogenesis is inadequately understood. HEV encodes three open reading frames (ORFs): ORF1 (replicative machinery), ORF2 (viral capsid) essential for (infectious particles formation) and ORF3 (viral release). The presence of known and unknown coding and non-coding regions of HEV ORFs are still debated. Viral proteins entail disordered regions which are linked with the infectivity and pathogenicity of virus. Thus, we examined the dark proteome of HEV through analyzing intrinsically disordered protein regions (IDPRs) present in the ORFs by exploiting computational methodologies. Our findings suggested that ORF3 had the highest prevalence of disordered regions. The ORF3 region was followed by ORF2, which had comparatively lesser fraction of intrinsic disorder. The ORF1 had the least number of disordered residues in the HEV proteome. Our intrinsic disorder analysis results revealed that ORF1 polyprotein consists of mostly ordered domains, i.e., proteins having significant level of well-defined structures, with the exclusion of Pro and PCP domains. The analysis reveals Pro domain as a highly disordered protein while PCP domain as an intrinsic disordered protein. MoRF analysis revealed that HEV proteome contains multiple MoRFs across all ORFs. IDPRs are characterized by remarkable conformational flexibility and structural plasticity resulting in their engagement in several biological processes. Due to possession of MoRF in the HEV proteins, these regions can be used for protein-protein interactions due to the structural flexibility. IDPRs are characterized by remarkable conformational flexibility and structural plasticity resulting in their engagement in several biological processes. Due to possession of MoRF in the HEV proteins, these regions can be used for protein-protein interactions due to the structural flexibility. These extensive findings on the HEV proteome will have significant implications in understanding the deeper functioning of structural as well as non-structural biology of HEV proteins.

Hepatitis E virus (HEV) is a positive-sense RNA virus belonging to the family Hepeviridae. The genome of HEV is organized into three open-reading frames (ORFs): ORF1, ORF2, and ORF3. The ORF1 non-structural Y-domain region (YDR) has been demonstrated to play an important role in the HEV pathogenesis. The nucleotide composition, synonymous codon usage bias in conjunction with other factors influencing the viral YDR genes of HEV have not been studied. Codon usage represents a significant mechanism in establishing the host-pathogen relationship. The present study for the first time elucidates the detailed codon usage patterns of YDR among HEV and HEV-hosts (Human, Rabbit, Mongoose, Pig, Wild boar, Camel, Monkey). The overall nucleotide composition revealed the abundance of C and U nucleotides in YDR genomes. The relative synonymous codon usage (RSCU) analysis indicated biasness towards C and U over A and G ended codons in HEV across all hosts. Codon frequency comparative analyses among HEV-hosts showed both similarities and discrepancies in usage of preferred codons encoding amino acids, which revealed that HEV codon preference neither completely differed nor completely showed similarity with its hosts. Thus, our results clearly indicated that the synonymous codon usage of HEV is a mixture of the two types of codon usage: coincidence and antagonism. Mutation pressure from virus and natural selection from host seems to be accountable for shaping the codon usage patterns in YDR. The study emphasised that the influence of compositional constraints, codon usage biasness, mutational alongside the selective forces were reflected in the occurrence of YDR codon usage patterns. Our study is the first in its kind to have reported the analysis of codon usage patterns on a total of seven different natural HEV hosts. Therefore, knowledge of preferred codons obtained from our study will not only augment our understanding towards molecular evolution but is also envisaged to provide insight into the efficient viral expression, viral adaptation, and host effects on the HEV YDR codon usage.

Background Hepatitis E virus (HEV) is a member of the family Hepeviridae and causes acute HEV infections resulting in thousands of deaths worldwide. The zoonotic nature of HEV in addition to its tendency from human to human transmission has led scientists across the globe to work on its different aspects. HEV also accounts for about 30% mortality rates in case of pregnant women. The genome of HEV is organized into three open reading frames (ORFs): ORF1 ORF2 and ORF3. A reading frame encoded protein ORF4 has recently been discovered which is exclusive to GT 1 isolates of HEV. The ORF4 is suggested to play crucial role in pregnancy-associated pathology and enhanced replication. Though studies have documented the ORF4’s importance, the genetic features of ORF4 protein genes in terms of compositional patterns have not been elucidated. As codon usage performs critical role in establishment of the host–pathogen relationship, therefore, the present study reports the codon usage analysis (based on nucleotide sequences of HEV ORF4 available in the public database) in three hosts along with the factors influencing the codon usage patterns of the protein genes of ORF4 of HEV. Results The nucleotide composition analysis indicated that ORF4 protein genes showed overrepresentation of C nucleotide and while A nucleotide was the least-represented, with random distribution of G and T(U) nucleotides. The relative synonymous codon usage (RSCU) analysis revealed biasness toward C/G-ended codons (over U/A) in all three natural HEV-hosts (human, rat and ferret). It was observed that all the ORF4 genes were richly endowed with GC content. Further, our results showed the occurrence of both coincidence and antagonistic codon usage patterns among HEV-hosts. The findings further emphasized that both mutational and selection forces influenced the codon usage patterns of ORF4 protein genes. Conclusions To the best of our knowledge, this is first bioinformatics study evaluating codon usage patterns in HEV ORF4 protein genes. The findings from this study are expected to increase our understanding toward significant factors involved in evolutionary changes of ORF4.

Hepatitis E is a liver disease caused by the pathogen hepatitis E virus (HEV). The largest polyprotein open reading frame 1 (ORF1) contains a nonstructural Y-domain region (YDR) whose activity in HEV adaptation remains uncharted. The specific role of disordered regions in several nonstructural proteins has been demonstrated to participate in the multiplication and multiple regulatory functions of the viruses. Thus, intrinsic disorder of YDR including its structural and functional annotation was comprehensively studied by exploiting computational methodologies to delineate its role in viral adaptation. Based on our findings, it was evident that YDR contains significantly higher levels of ordered regions with less prevalence of disordered residues. Sequence-based analysis of YDR revealed it as a \"dual personality\" (DP) protein due to the presence of both structured and unstructured (intrinsically disordered) regions. The evolution of YDR was shaped by pressures that lead towards predominance of both disordered and regularly folded amino acids (Ala, Arg, Gly, Ile, Leu, Phe, Pro, Ser, Tyr, Val). Additionally, the predominance of characteristic DP residues (Thr, Arg, Gly, and Pro) further showed the order as well as disorder characteristic possessed by YDR. The intrinsic disorder propensity analysis of YDR revealed it as a moderately disordered protein. All the YDR sequences consisted of molecular recognition features (MoRFs), i.e., intrinsic disorder-based protein-protein interaction (PPI) sites, in addition to several nucleotide-binding sites. Thus, the presence of molecular recognition (PPI, RNA binding, and DNA binding) signifies the YDR's interaction with specific partners, host membranes leading to further viral infection. The presence of various disordered-based phosphorylation sites further signifies the role of YDR in various biological processes. Furthermore, functional annotation of YDR revealed it as a multifunctional-associated protein, due to its susceptibility in binding to a wide range of ligands and involvement in various catalytic activities. As DP are targets for regulation, thus, YDR contributes to cellular signaling processes through PPIs. As YDR is incompletely understood, therefore, our data on disorder-based function could help in better understanding its associated functions. Collectively, our novel data from this comprehensive investigation is the first attempt to delineate YDR role in the regulation and pathogenesis of HEV.

Background Hepatitis E virus (HEV) of the family Hepeviridae is a major causative agent of acute hepatitis in developing countries. The Y-domain is derived from multi-domain non-structural polyprotein encoded by open reading frame 1 (ORF1). Previous studies have demonstrated the essentiality of Y-domain sequences in HEV life cycle; however, its function remains completely unexplored. The following study was thus conceptualized to examine the detailed computational investigation for the putative Y-domain to estimate its phylogenetic assessment, physiochemical properties, structural and functional characteristics using in silico analyses. Results The phylogenetic assessment of Y-domain with a vast range of hosts indicated that the protein was very well conserved throughout the course of evolution. The Y-domain was found to be unstable, hydrophilic and basic in nature with high thermostability value. Structural analysis of Y-domain revealed mixed α/β structural fold of the protein having higher percentage of alpha-helices. The three-dimensional (3D) protein model generated through homology modelling revealed the presence of clefts, tunnels and pore. Gene ontology analysis predicted Y-domain protein’s involvement in several binding and catalytic activities as well as significant biological processes. Mutations in the conserved amino acids of the Y-domain suggested that it may stabilize or de-stabilize the protein structure that might affect its structure–function relationship. Conclusions This theoretical study will facilitate towards deciphering the role of unexplored Y-domain, thereby providing better understanding towards the pathogenesis of HEV infection.