Viral Membrane Channels: Role and Function in the Virus Life Cycle

Tackling Influenza A virus by M2 ion channel blockers: Latest progress and limitations

Influenza outbreaks cause pandemics in millions of people. The treatment of influenza remains a challenge due to significant genetic polymorphism in the influenza virus. Also, developing vaccines to protect against seasonal and pandemic influenza infections is constantly impeded. Thus, antibiotics are the only first line of defense against antigenically distinct strains or new subtypes of influenza viruses. Among several anti-influenza targets, the M2 protein of the influenza virus performs several activities. M2 protein is an ion channel that permits proton conductance through the virion envelope and the deacidification of the Golgi apparatus. Both these functions are critical for viral replication. Thus, targeting the M2 protein of the influenza virus is an essential target. Rimantadine and amantadine are two well-known drugs that act on the M2 protein. However, these drugs acquired resistance to influenza and thus are not recommended to treat influenza infections. This review discusses an overview of anti-influenza therapy, M2 ion channel functions, and its working principle. It also discusses the M2 structure and its role, and the change in the structure leads to mutant variants of influenza A virus. We also shed light on the recently identified compounds acting against wild-type and mutated M2 proteins of influenza virus A. These scaffolds could be an alternative to M2 inhibitors and be developed as antibiotics for treating influenza infections.

Microbial membrane transport proteins and their biotechnological applications

Because of the hydrophobic nature of the membrane lipid bilayer, the majority of the hydrophilic solutes require special transportation mechanisms for passing through the cell membrane. Integral membrane transport proteins (MTPs), which belong to the Major Intrinsic Protein Family, facilitate the transport of these solutes across cell membranes. MTPs including aquaporins and carrier proteins are transmembrane proteins spanning across the cell membrane. The easy handling of microorganisms enabled the discovery of a remarkable number of transport proteins specific to different substances. It has been realized that these transporters have very important roles in the survival of microorganisms, their pathogenesis, and antimicrobial resistance. Astonishing features related to the solute specificity of these proteins have led to the acceleration of the research on the discovery of their properties and the development of innovative products in which these unique properties are used or imitated. Studies on microbial MTPs range from the discovery and characterization of a novel transporter protein to the mining and screening of them in a large transporter library for particular functions, from simulations and modeling of specific transporters to the preparation of biomimetic synthetic materials for different purposes such as biosensors or filtration membranes. This review presents recent discoveries on microbial membrane transport proteins and focuses especially on formate nitrite transport proteins and aquaporins, and advances in their biotechnological applications.

SARS-CoV-2 accessory proteins ORF7a and ORF3a use distinct mechanisms to down-regulate MHC-I surface expression

Major histocompatibility complex class I (MHC-I) molecules, which are dimers of a glycosylated polymorphic transmembrane heavy chain and the small-protein β₂-microglobulin (β₂m), bind peptides in the endoplasmic reticulum that are generated by the cytosolic turnover of cellular proteins. In virus-infected cells, these peptides may include those derived from viral proteins. Peptide-MHC-I complexes then traffic through the secretory pathway and are displayed at the cell surface where those containing viral peptides can be detected by CD8⁺ T lymphocytes that kill infected cells. Many viruses enhance their in vivo survival by encoding genes that down-regulate MHC-I expression to avoid CD8⁺ T cell recognition. Here, we report that two accessory proteins encoded by SARS-CoV-2, the causative agent of the ongoing COVID-19 pandemic, down-regulate MHC-I expression using distinct mechanisms. First, ORF3a, a viroporin, reduces the global trafficking of proteins, including MHC-I, through the secretory pathway. The second, ORF7a, interacts specifically with the MHC-I heavy chain, acting as a molecular mimic of β₂m to inhibit its association. This slows the exit of properly assembled MHC-I molecules from the endoplasmic reticulum. We demonstrate that ORF7a reduces antigen presentation by the human MHC-I allele HLA-A*02:01. Thus, both ORF3a and ORF7a act post-translationally in the secretory pathway to lower surface MHC-I expression, with ORF7a exhibiting a specific mechanism that allows immune evasion by SARS-CoV-2.

SARS-CoV-2 accessory proteins ORF7a and ORF3a use distinct mechanisms to downregulate MHC-I surface expression

Major histocompatibility complex class I (MHC-I) molecules, which are dimers of a glycosylated polymorphic transmembrane heavy chain and the small protein β 2 -microglobulin (β 2 m), bind peptides in the endoplasmic reticulum that are generated by the cytosolic turnover of cellular proteins. In virus-infected cells these peptides may include those derived from viral proteins. Peptide-MHC-I complexes then traffic through the secretory pathway and are displayed at the cell surface where those containing viral peptides can be detected by CD8 + T lymphocytes that kill infected cells. Many viruses enhance their in vivo survival by encoding genes that downregulate MHC-I expression to avoid CD8 + T cell recognition. Here we report that two accessory proteins encoded by SARS-CoV-2, the causative agent of the ongoing COVID-19 pandemic, downregulate MHC-I expression using distinct mechanisms. One, ORF3a, a viroporin, reduces global trafficking of proteins, including MHC-I, through the secretory pathway. The second, ORF7a, interacts specifically with the MHC-I heavy chain, acting as a molecular mimic of β 2 m to inhibit its association. This slows the exit of properly assembled MHC-I molecules from the endoplasmic reticulum. We demonstrate that ORF7a reduces antigen presentation by the human MHC-I allele HLA-A*02:01. Thus, both ORF3a and ORF7a act post-translationally in the secretory pathway to lower surface MHC-I expression, with ORF7a exhibiting a novel and specific mechanism that allows immune evasion by SARS-CoV-2.

Significance Statement

Viruses may down-regulate MHC class I expression on infected cells to avoid elimination by cytotoxic T cells. We report that the accessory proteins ORF7a and ORF3a of SARS-CoV-2 mediate this function and delineate the two distinct mechanisms involved. While ORF3a inhibits global protein trafficking to the cell surface, ORF7a acts specifically on MHC-I by competing with β 2 m for binding to the MHC-I heavy chain. This is the first account of molecular mimicry of β 2 m as a viral mechanism of MHC-I down-regulation to facilitate immune evasion.

Discovery and Characterization of the Phospholemman/SIMP/Viroporin Superfamily

Using bioinformatic approaches, we present evidence of distant relatedness among the Ephemerovirus Viroporin family, the Rhabdoviridae Putative Viroporin U5 family, the Phospholemman family, and the Small Integral Membrane Protein family. Our approach is based on the transitivity property of homology complemented with five validation criteria: (1) significant sequence similarity and alignment coverage, (2) compatibility of topology of transmembrane segments, (3) overlap of hydropathy profiles, (4) conservation of protein domains, and (5) conservation of sequence motifs. Our results indicate that Pfam protein domains PF02038 and PF15831 can be found in or projected onto members of all four families. In addition, we identified a 26-residue motif conserved across the superfamily. This motif is characterized by hydrophobic residues that help anchor the protein to the membrane and charged residues that constitute phosphorylation sites. In addition, all members of the four families with annotated function are either responsible for or affect the transport of ions into and/or out of the cell. Taken together, these results justify the creation of the novel Phospholemman/SIMP/Viroporin superfamily. Given that transport proteins can be found not just in cells, but also in viruses, the ability to relate viroporin protein families with their eukaryotic and bacterial counterparts is an important development in this superfamily.

Identification of existing pharmaceuticals and herbal medicines as inhibitors of SARS-CoV-2 infection

The outbreak of COVID-19 caused by SARS-CoV-2 has resulted in more than 50 million confirmed cases and over 1 million deaths worldwide as of November 2020. Currently, there are no effective antivirals approved by the Food and Drug Administration to contain this pandemic except the antiviral agent remdesivir. In addition, the trimeric spike protein on the viral surface is highly glycosylated and almost 200,000 variants with mutations at more than 1,000 positions in its 1,273 amino acid sequence were reported, posing a major challenge in the development of antibodies and vaccines. It is therefore urgently needed to have alternative and timely treatments for the disease. In this study, we used a cell-based infection assay to screen more than 3,000 agents used in humans and animals, including 2,855 small molecules and 190 traditional herbal medicines, and identified 15 active small molecules in concentrations ranging from 0.1 nM to 50 μM. Two enzymatic assays, along with molecular modeling, were then developed to confirm those targeting the virus 3CL protease and the RNA-dependent RNA polymerase. Several water extracts of herbal medicines were active in the cell-based assay and could be further developed as plant-derived anti-SARS-CoV-2 agents. Some of the active compounds identified in the screen were further tested in vivo, and it was found that mefloquine, nelfinavir, and extracts of Ganoderma lucidum (RF3), Perilla frutescens, and Mentha haplocalyx were effective in a challenge study using hamsters as disease model.

Anti-COVID-19 drug candidates: A review on potential biological activities of natural products in the management of new coronavirus infection

Background and aim

The novel coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is now become a worldwide pandemic bringing over 71 million confirmed cases, while the specific drugs and vaccines approved for this disease are still limited regarding their effectiveness and adverse events. Since virus incidences are still on rise, infectivity and mortality may also rise in the near future, natural products are highly considered to be valuable sources for the discovery of new antiviral drugs against SARS-CoV-2. This present review aims to comprehensively summarize the up-to-date scientific literatures on biological activities of plant- and mushroom-derived compounds relevant to mechanistic targets involved in SARS-CoV-2 infection and inflammatory-associated pathogenesis, including viral entry, replication and release, and the renin-angiotensin-aldosterone system (RAAS).

Experimental procedure

Data were retrieved from a literature search available on PubMed, Scopus and Google Scholar databases and collected until the end of May 2020. The findings from in vitro cell and non-cell based studies were considered, while the results of in silico studies were excluded.

Results and conclusion

Based on the previous findings in SARS-CoV studies, except in silico molecular docking analysis, herein, we provide a total of 150 natural compounds as potential candidates for development of new anti-COVID-19 drugs with higher efficacy and lower toxicity than the existing therapeutic agents. Several natural compounds have showed their promising actions on multiple therapeutic targets, which should be further explored. Among them, quercetin, one of the most abundant of plant flavonoids, is proposed as a lead candidate with its ability on the virus side to inhibit SARS-CoV spike protein-angiotensin-converting enzyme 2 (ACE2) interaction, viral protease and helicase activities, as well as on the host cell side to inhibit ACE activity and increase intracellular zinc level.

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Relevant and up-to-date publications in natural products with anti-COVID-19 potential.

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Emphasis on the potential of anti-COVID-19 plant/mushroom-based medicine.

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Twenty four proposed natural compounds for the anti-COVID-19 drug candidates.

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Quercetin emerged as the most promising compound acting on multiple therapeutic targets.

Similarities between the effect of SARS-CoV-2 and HCV on the cellular level, and the possible role of ion channels in COVID19 progression: a review of potential targets for diagnosis and treatment

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has prompted an urgent need to identify effective medicines for the prevention and treatment of the disease. A comparative analysis between SARS-CoV-2 and Hepatitis C Virus (HCV) can expand the available knowledge regarding the virology and potential drug targets against these viruses. Interestingly, comparing HCV with SARS-CoV-2 reveals major similarities between them, ranging from the ion channels that are utilized, to the symptoms that are exhibited by patients. Via this comparative analysis, and from what is known about HCV, the most promising treatments for COVID-19 can focus on the reduction of viral load, treatment of pulmonary system damages, and reduction of inflammation. In particular, the drugs that show most potential in this regard include ritonavir, a combination of peg-IFN, and lumacaftor-ivacaftor. This review anaylses SARS-CoV-2 from the perspective of the role of ion homeostasis and channels in viral pathomechanism. We also highlight other novel treatment approaches that can be used for both treatment and prevention of COVID-19. The relevance of this review is to offer high-quality evidence that can be used as the basis for the identification of potential solutions to the COVID-19 pandemic.

Lipidomics Issues on Human Positive ssRNA Virus Infection: An Update

The pathogenic mechanisms underlying the Biology and Biochemistry of viral infections are known to depend on the lipid metabolism of infected cells. From a lipidomics viewpoint, there are a variety of mechanisms involving virus infection that encompass virus entry, the disturbance of host cell lipid metabolism, and the role played by diverse lipids in regard to the infection effectiveness. All these aspects have currently been tackled separately as independent issues and focused on the function of proteins. Here, we review the role of cholesterol and other lipids in ssRNA+ infection.

Polycistronic Genome Segment Evolution and Gain and Loss of FAST Protein Function during Fusogenic Orthoreovirus Speciation

The Reoviridae family is the only non-enveloped virus family with members that use syncytium formation to promote cell–cell virus transmission. Syncytiogenesis is mediated by a fusion-associated small transmembrane (FAST) protein, a novel family of viral membrane fusion proteins. Previous evidence suggested the fusogenic reoviruses arose from an ancestral non-fusogenic virus, with the preponderance of fusogenic species suggesting positive evolutionary pressure to acquire and maintain the fusion phenotype. New phylogenetic analyses that included the atypical waterfowl subgroup of avian reoviruses and recently identified new orthoreovirus species indicate a more complex relationship between reovirus speciation and fusogenic capacity, with numerous predicted internal indels and 5’-terminal extensions driving the evolution of the orthoreovirus’ polycistronic genome segments and their encoded FAST and fiber proteins. These inferred recombination events generated bi- and tricistronic genome segments with diverse gene constellations, they occurred pre- and post-orthoreovirus speciation, and they directly contributed to the evolution of the four extant orthoreovirus FAST proteins by driving both the gain and loss of fusion capability. We further show that two distinct post-speciation genetic events led to the loss of fusion in the waterfowl isolates of avian reovirus, a recombination event that replaced the p10 FAST protein with a heterologous, non-fusogenic protein and point substitutions in a conserved motif that destroyed the p10 assembly into multimeric fusion platforms.

Dengue Virus Serotype 2 and Its Non-Structural Proteins 2A and 2B Activate NLRP3 Inflammasome

Dengue is the most prevalent and rapidly transmitted mosquito-borne viral disease of humans. One of the fundamental innate immune responses to viral infections includes the processing and release of pro-inflammatory cytokines such as interleukin (IL-1β and IL-18) through the activation of inflammasome. Dengue virus stimulates the Nod-like receptor (NLRP3-specific inflammasome), however, the specific mechanism(s) by which dengue virus activates the NLRP3 inflammasome is unknown. In this study, we investigated the activation of the NLRP3 inflammasome in endothelial cells (HMEC-1) following dengue virus infection. Our results showed that dengue infection as well as the NS2A and NS2B protein expression increase the NLRP3 inflammasome activation, and further apoptosis-associated speck-like protein containing caspase recruitment domain (ASC) oligomerization, and IL-1β secretion through caspase-1 activation. Specifically, we have demonstrated that NS2A and NS2B, two proteins of dengue virus that behave as putative viroporins, were sufficient to stimulate the NLRP3 inflammasome complex in lipopolysaccharide (LPS)-primed endothelial cells. In summary, our observations provide insight into the dengue-induced inflammatory response mechanism and highlight the importance of DENV-2 NS2A and NS2B proteins in activation of the NLRP3 inflammasome during dengue virus infection.

Recovirus NS1-2 Has Viroporin Activity That Induces Aberrant Cellular Calcium Signaling To Facilitate Virus Replication

Enteric viruses in the Caliciviridae family cause acute gastroenteritis in humans and animals, but the cellular processes needed for virus replication and disease remain unknown. A common strategy among enteric viruses, including rotaviruses and enteroviruses, is to encode a viral ion channel (i.e., viroporin) that is targeted to the endoplasmic reticulum (ER) and disrupts host calcium (Ca2+) homeostasis. Previous reports have demonstrated genetic and functional similarities between the nonstructural proteins of caliciviruses and enteroviruses, including the calicivirus NS1-2 protein and the 2B viroporin of enteroviruses. However, it is unknown whether caliciviruses alter Ca2+ homeostasis for virus replication or whether the NS1-2 protein has viroporin activity like its enterovirus counterpart. To address these questions, we used Tulane virus (TV), a rhesus enteric calicivirus, to examine Ca2+ signaling during infection and determine whether NS1-2 has viroporin activity that disrupts Ca2+ homeostasis. We found that TV increases Ca2+ signaling during infection and that increased cytoplasmic Ca2+ levels are important for efficient replication. Further, TV NS1-2 localizes to the endoplasmic reticulum, the predominant intracellular Ca2+ store, and the NS2 region has characteristics of a viroporin domain (VPD). NS1-2 had viroporin activity in a classic bacterial functional assay and caused aberrant Ca2+ signaling when expressed in mammalian cells, but truncation of the VPD abrogated these activities. Together, our data provide new mechanistic insights into the function of the NS2 region of NS1-2 and support the premise that enteric viruses, including those within Caliciviridae, exploit host Ca2+ signaling to facilitate their replication.IMPORTANCE Tulane virus is one of many enteric caliciviruses that cause acute gastroenteritis and diarrheal disease. Globally, enteric caliciviruses affect both humans and animals and amass >65 billion dollars per year in treatment and health care-associated costs, thus imposing an enormous economic burden. Recent progress has resulted in several cultivation systems (B cells, enteroids, and zebrafish larvae) to study human noroviruses, but mechanistic insights into the viral factors and host pathways important for enteric calicivirus replication and infection are still largely lacking. Here, we used Tulane virus, a calicivirus that is biologically similar to human noroviruses and can be cultivated by conventional cell culture, to identify and functionally validate NS1-2 as an enteric calicivirus viroporin. Viroporin-mediated calcium signaling may be a broadly utilized pathway for enteric virus replication, and its existence within caliciviruses provides a novel approach to developing antivirals and comprehensive therapeutics for enteric calicivirus diarrheal disease outbreaks.

Potential Viroporin Candidates From Pathogenic Viruses Using Bacteria-Based Bioassays

Viroporins are a family of small hydrophobic proteins found in many enveloped viruses that are capable of ion transport. Building upon the ability to inhibit influenza by blocking its archetypical M2 H⁺ channel, as a family, viroporins may represent a viable target to curb viral infectivity. To this end, using three bacterial assays we analyzed six small hydrophobic proteins from biomedically important viruses as potential viroporin candidates. Our results indicate that Eastern equine encephalitis virus 6k, West Nile virus MgM, Dengue virus 2k, Dengue virus P1, Variola virus gp170, and Variola virus gp151 proteins all exhibit channel activity in the bacterial assays, and as such may be considered viroporin candidates. It is clear that more studies, such as patch clamping, will be needed to characterize the ionic conductivities of these proteins. However, our approach presents a rapid procedure to analyze open reading frames in other viruses, yielding new viroporin candidates for future detailed investigation. Finally, if conductivity is proven vital to their cognate viruses, the bio-assays presented herein afford a simple approach to screen for new channel blockers.

The Saffold Virus-Penang 2B and 3C Proteins, but not the L Protein, Induce Apoptosis in HEp-2 and Vero Cells

Our previous work has shown that Saffold virus (SAFV) induced several rodent and primate cell lines to undergo apoptosis (Xu et al. in Emerg Microb Infect 3:1-8, 2014), but the essential viral proteins of SAFV involved in apoptotic activity lack study. In this study, we individually transfected the viral proteins of SAFV into HEp-2 and Vero cells to assess their ability to induce apoptosis, and found that the 2B and 3C proteins are proapoptotic. Further investigation indicated the transmembrane domain of the 2B protein is essential for the apoptotic activity and tetramer formation of the 2B protein. Our research provides clues for the possible mechanisms of apoptosis induced by SAFV in different cell lines. It also opens up new directions to study viral proteins (the 2B, 3C protein), and sets the stage for future exploration of any possible link between SAFV, inclusive of its related uncultivable genotypes, and multiple sclerosis.

Endometriosis-related ceRNA network to identify predictive biomarkers of endometrial receptivity

AIM

As RNA, which plays a role in the regulation of endometrial receptivity, can be modulated via ceRNA mechanisms, we constructed a ceRNA network to explore potential RNA/ceRNA biomarkers indicating endometrial receptivity associated with endometriosis.

MATERIALS & METHODS

RNA sequencing was performed on eutopic endometrium from eight patients with and without endometriosis. Bioinformatics algorithms were used to predict ceRNA network and pathway analysis.

RESULTS

We identified an endometriosis-associated ceRNA network involving 45 pathways and four ceRNAs as potential predictive biomarkers for endometrial receptivity. Patients with endometriosis presented lower levels of progesterone receptor type B expression.

CONCLUSION

Differentially expressed RNAs and lower progesterone receptors type B levels in endometriosis might be related to the impairment of endometrial receptivity.

Genes for Membrane Transport Proteins: Not So Rare in Viruses

Some viruses have genes encoding proteins with membrane transport functions. It is unknown if these types of proteins are rare or are common in viruses. In particular, the evolutionary origin of some of the viral genes is obscure, where other viral proteins have homologs in prokaryotic and eukaryotic organisms. We searched virus genomes in databases looking for transmembrane proteins with possible transport function. This effort led to the detection of 18 different types of putative membrane transport proteins indicating that they are not a rarity in viral genomes. The most abundant proteins are K⁺ channels. Their predicted structures vary between different viruses. With a few exceptions, the viral proteins differed significantly from homologs in their current hosts. In some cases the data provide evidence for a recent gene transfer between host and virus, but in other cases the evidence indicates a more complex evolutionary history.

Molecular design, synthesis and biological evaluation of cage compound-based inhibitors of hepatitis C virus p7 ion channels

The hepatitis C caused by the hepatitis C virus (HCV) is an acute and/or chronic liver disease ranging in severity from a mild brief ailment to a serious lifelong illness that affects up to 3% of the world population and imposes significant and increasing social, economic, and humanistic burden. Over the past decade, its treatment was revolutionized by the development and introduction into clinical practice of the direct acting antiviral (DAA) agents targeting the non-structural viral proteins NS3/4A, NS5A, and NS5B. However, the current treatment options still have important limitations, thus, the development of new classes of DAAs acting on different viral targets and having better pharmacological profile is highly desirable. The hepatitis C virus p7 viroporin is a relatively small hydrophobic oligomeric viral ion channel that plays a critical role during virus assembly and maturation, making it an attractive and validated target for the development of the cage compound-based inhibitors. Using the homology modeling, molecular dynamics, and molecular docking techniques, we have built a representative set of models of the hepatitis C virus p7 ion channels (Gt1a, Gt1b, Gt1b_L20F, Gt2a, and Gt2b), analyzed the inhibitor binding sites, and identified a number of potential broad-spectrum inhibitor structures targeting them. For one promising compound, the binding to these targets was additionally confirmed and the binding modes and probable mechanisms of action were clarified by the molecular dynamics simulations. A number of compounds were synthesized, and the tests of their antiviral activity (using the BVDV model) and cytotoxicity demonstrate their potential therapeutic usefulness and encourage further more detailed studies. The proposed approach is also suitable for the design of broad-spectrum ligands interacting with other multiple labile targets including various viroporins.

Viral Short ORFs and Their Possible Functions

Definition of functional genomic elements is one of the greater challenges of the genomic era. Traditionally, putative short open reading frames (sORFs) coding for less than 100 amino acids were disregarded due to computational and experimental limitations; however, it has become clear over the past several years that translation of sORFs is pervasive and serves diverse functions. The development of ribosome profiling, allowing identification of translated sequences genome wide, revealed wide spread, previously unidentified translation events. New computational methodologies as well as improved mass spectrometry approaches also contributed to the task of annotating translated sORFs in different organisms. Viruses are of special interest due to the selective pressure on their genome size, their rapid and confining evolution, and the potential contribution of novel peptides to the host immune response. Indeed, many functional viral sORFs were characterized to date, and ribosome profiling analyses suggest that this may be the tip of the iceberg. Our computational analyses of sORFs identified by ribosome profiling in DNA viruses demonstrate that they may be enriched in specific features implying that at least some of them are functional. Combination of systematic genome editing strategies with synthetic tagging will take us into the next step-elucidation of the biological relevance and function of this intriguing class of molecules.

Reviewing the evidence for viruses as environmental risk factors for ALS: A new perspective

Amyotrophic lateral sclerosis is a devastating neurodegenerative disease whose etiology remains poorly understood. Since the genetic basis of disease is known in only a small subset of cases, there has been substantial interest in determining whether environmental factors act as triggers of ALS. Viruses have received longstanding attention as potential ALS triggers. Yet, existing studies have not provided a compelling case for causation. This review summarizes the evidence supporting a link between viral infection and motor neuron disease, with a focus on ALS. Limitations of prior studies are discussed and contextualized, and recent work that has provided stronger mechanistic evidence for viruses in disease pathogenesis is highlighted. Finally, we offer a new perspective on the association of viruses with ALS, and underscore the need for multidisciplinary approaches bridging neurology and infectious diseases research to move the field forward in the future.

Viral dependence on cellular ion channels - an emerging anti-viral target?

The broad range of cellular functions governed by ion channels represents an attractive target for viral manipulation. Indeed, modulation of host cell ion channel activity by viral proteins is being increasingly identified as an important virus-host interaction. Recent examples have demonstrated that virion entry, virus egress and the maintenance of a cellular environment conducive to virus persistence are, in part, dependent on virus manipulation of ion channel activity. Most excitingly, evidence has emerged that targeting ion channels pharmacologically can impede virus life cycles. Here, we discuss current examples of virus-ion channel interactions and the potential of targeting ion channel function as a new, pharmacologically safe and broad-ranging anti-viral therapeutic strategy.

Hepatitis E virus ORF3 is a functional ion channel required for release of infectious particles

Hepatitis E virus (HEV) is the leading cause of enterically transmitted viral hepatitis globally. Of HEV's three ORFs, the function of ORF3 has remained elusive. Here, we demonstrate that via homophilic interactions ORF3 forms multimeric complexes associated with intracellular endoplasmic reticulum (ER)-derived membranes. HEV ORF3 shares several structural features with class I viroporins, and the function of HEV ORF3 can be maintained by replacing it with the well-characterized viroporin influenza A virus (IAV) matrix-2 protein. ORF3's ion channel function is further evidenced by its ability to mediate ionic currents when expressed in Xenopus laevis oocytes. Furthermore, we identified several positions in ORF3 critical for its formation of multimeric complexes, ion channel activity, and, ultimately, release of infectious particles. Collectively, our data demonstrate a previously undescribed function of HEV ORF3 as a viroporin, which may serve as an attractive target in developing direct-acting antivirals.

Characterization of Viral Exposures in United States Occupational Environments

Viruses are considered to be the most abundant biological particles and have the capability to infect all forms of life leading to a variety of diseases. American workers in specific occupational environments are threatened by viral exposures, highlighting the importance to recognize the type and risk of exposure, as well as the preventive measures that can be taken to reduce the risk of exposure. For example, healthcare workers can potentially be exposed to air and blood-borne pathogens, such as hepatitis and the human immunodeficiency virus. These types of exposures have led to the development of preventive equipment and regulations intended to reduce viral exposures in occupational settings. This chapter will discuss the characteristics of viruses and the occupationally relevant viruses of which people in varying occupations can potentially encounter. Regulatory guidelines and protective strategies will also be reviewed.