Viral protease inhibitors

Utilizing sinapic acid as an inhibitory antiviral agent against MERS-CoV PLpro

Concerns about the social and economic collapse, high mortality rates, and stress on the healthcare system are developing due to the coronavirus onslaught in the form of various species and their variants. In the recent past, infections brought on by coronaviruses severe acute respiratory syndrome coronaviruses (SARS-CoV and SARS-CoV-2) as well as middle east respiratory syndrome coronavirus (MERS-CoV) have been reported. There is a severe lack of medications to treat various coronavirus types including MERS-CoV which is hazard to public health due to its ability for pandemic spread by human-to-human transmission. Here, we utilized sinapic acid (SA) against papain-like protease (PLpro), a crucial enzyme involved in MERS-CoV replication, because phytomedicine derived from nature has less well-known negative effects. The thermal shift assay (TSA) was used in the current study to determine whether the drug interact with the recombinant MERS-CoV PLpro. Also, inhibition assay was conducted as the hydrolysis of fluorogenic peptide from the Z-RLRGG-AMC-peptide bond in the presence of SA to determine the level of inhibition of the MERS-CoV PLpro. To study the structural binding efficiency Autodock Vina was used to dock SA to the MERS-CoV PLpro and results were analyzed using PyMOL and Maestro Schrödinger programs. Our results show a convincing interaction between SA and the MERS protease, as SA reduced MERS-CoV PLpro in a dose-dependent way IC50 values of 68.58 μM (of SA). The TSA showed SA raised temperature of melting to 54.61 °C near IC50 and at approximately 2X IC50 concentration (111.5 μM) the Tm for SA + MERS-CoV PLpro was 59.72 °C. SA was docked to MERS-CoV PLpro to identify the binding site. SA bound to the blocking loop (BL2) region of MERS-CoV PLpro interacts with F268, E272, V275, and P249 residues of MERS-CoV PLpro. The effectiveness of protease inhibitors against MERS-CoV has been established and SA is already known for broad range biological activity including antiviral properties; it can be a suitable candidate for anti-MERS-CoV treatment.

A Non-Active-Site Inhibitor with Selectivity for Zika Virus NS2B-NS3 Protease

Flavivirus infection usually results in fever accompanied by headache, arthralgia, and, in some cases, rash. Although the symptoms are mild, full recovery can take several months. Flaviviruses encode seven nonstructural proteins that represent potential drug targets for this viral family. Focusing on the Zika virus NS2B-NS3 protease, we uncovered a unique inhibitor, MH1, composed of aminothiazolopyridine and benzofuran moieties. MH1 inhibits ZVP with a biochemical IC50 of 440 nM and effectively blocks cleavage of ZVP substrates in cells. Surprisingly, MH1 inhibits the other flaviviral proteases at least 18-fold more weakly. This same phenomenon was observed in assays of the viral cytopathic effect, where only Zika virus showed sensitivity to MH1. This selectivity was unexpected since flaviviral proteases have high similarity in sequence and protein structure. MH1 binds at an allosteric site, as demonstrated by its ability to stabilize ZVP synergistically with an active site inhibitor. To understand its selectivity, we constructed a series of hybrid proteases composed of select segments of ZVP, which is sensitive to MH1, and dengue virus protease, which is essentially insensitive to MH1. Our results suggest that MH1 binds to the NS3 protease domain, disrupting its interaction with NS2B. These interactions are essential for substrate binding and cleavage. In particular, the unique dynamic properties of NS2B from Zika seem to be required for the function of MH1. Insights into the mechanism of MH1 function will aid us in developing non-active-site-directed, pan-flaviviral inhibitors, by highlighting the importance of evaluating and considering the dynamics of the NS2B regions.

[Options for treatment of feline infectious peritonitis - previously and today]

Feline infectious peritonitis (FIP) is one of the most common infectious diseases in cats that is fatal when untreated. So far, there is no legally available effective treatment in Germany. Treatment options include only symptomatic treatment (e. g. glucocorticoids, propentofylline), immunomodulatory approaches (e. g. interferons, polyprenyl immunostimulant), and antiviral chemotherapy with protease inhibitors (e. g. GC376) or nucleoside analogues (e. g. GS-441524, remdesivir). Symptomatic treatment does not cure FIP but may lead to a short-term improvement of clinical signs in a subset of cats. Immunomodulatory treatment has also not shown to be very promising. In contrary, the antiviral compounds GS-441524 and GC376 exhibited significant efficacy in several studies and their use saved the lives of many cats suffering from FIP. However, both agents are currently not licensed and thus cannot be legally administered by veterinarians in Germany. Legally, cats may only be legally treated with GS-441524 in a few countries (e.g. Great Britain and Australia). In other countries, GS-441524 is imported by cat owners via the black market and administered on their own. This article provides an overview of the available treatment options and an outlook on the legal use of effective antiviral drugs.

Transmissible SARS-CoV-2 variants with resistance to clinical protease inhibitors

Vaccines and drugs have helped reduce disease severity and blunt the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, ongoing virus transmission, continuous evolution, and increasing selective pressures have the potential to yield viral variants capable of resisting these interventions. Here, we investigate the susceptibility of natural variants of the main protease [Mpro; 3C-like protease (3CLpro)] of SARS-CoV-2 to protease inhibitors. Multiple single amino acid changes in Mpro confer resistance to nirmatrelvir (the active component of Paxlovid). An additional clinical-stage inhibitor, ensitrelvir (Xocova), shows a different resistance mutation profile. Importantly, phylogenetic analyses indicate that several of these resistant variants have pre-existed the introduction of these drugs into the human population and are capable of spreading. These results encourage the monitoring of resistance variants and the development of additional protease inhibitors and other antiviral drugs with different mechanisms of action and resistance profiles for combinatorial therapy.

Myocarditis: causes, mechanisms, and evolving therapies

INTRODUCTION

Myocarditis is a severe lymphocyte-mediated inflammatory disorder of the heart, mostly caused by viruses and immune checkpoint inhibitors (ICIs). Recently, myocarditis as a rare adverse event of mRNA vaccines for SARS-CoV-2 has caused global attention. The clinical consequences of myocarditis can be very severe, but specific treatment options are lacking or not yet clinically proven.

AREAS COVERED

This paper offers a brief overview of the biology of viruses that frequently cause myocarditis, focusing on mechanisms important for viral entry and replication following host infection. Current and new potential therapeutic targets/strategies especially for viral myocarditis are reviewed systematically. In particular, the immune system in myocarditis is dissected with respect to infective viral and non-infective, ICI-induced myocarditis.

EXPERT OPINION

Vaccination is an excellent emerging preventative strategy for viral myocarditis, but most vaccines still require further development. Anti-viral treatments that inhibit viral replication need to be considered following viral infection in host myocardium, as lower viral load reduces inflammation severity. Understanding how the immune system continues to damage the heart even after viral clearance will define novel therapeutic targets/strategies. We propose that viral myocarditis can be best treated using a combination of antiviral agents and immunotherapies that control cytotoxic T cell activity.

Transmissible SARS-CoV-2 variants with resistance to clinical protease inhibitors

Vaccines and drugs have helped reduce disease severity and blunt the spread of SARS-CoV-2. However, ongoing virus transmission, continuous evolution, and increasing selective pressures have the potential to yield viral variants capable of resisting these interventions. Here, we investigate the susceptibility of natural variants of the main protease (Mpro/3CLpro) of SARS-CoV-2 to protease inhibitors. Multiple single amino acid changes in Mpro confer resistance to nirmatrelvir (the active component of Paxlovid). An additional clinical-stage inhibitor, ensitrelvir (Xocova), shows a different resistance mutation profile. Importantly, phylogenetic analyses indicate that several of these resistant variants have pre-existed the introduction of these drugs into the human population and are capable of spreading. These results encourage the monitoring of resistance variants and the development of additional protease inhibitors and other antiviral drugs with different mechanisms of action and resistance profiles for combinatorial therapy.

Drugs to limit Zika virus infection and implication for maternal-fetal health

Although the placenta has robust defense mechanisms that protect the fetus from a viral infection, some viruses can manipulate or evade these mechanisms and disrupt physiology or cross the placental barrier. It is well established that the Zika virus is capable of vertical transmission from mother to fetus and can cause malformation of the fetal central nervous system (i.e., microcephaly), as well as Guillain-Barre syndrome in adults. This review seeks to gather and assess the contributions of translational research associated with Zika virus infection, including maternal-fetal vertical transmission of the virus. Nearly 200 inhibitors that have been evaluated in vivo and/or in vitro for their therapeutic properties against the Zika virus are summarized in this review. We also review the status of current vaccine candidates. Our main objective is to provide clinically relevant information that can guide future research directions and strategies for optimized treatment and preventive care of infections caused by Zika virus or similar pathogens.

Proteolytic Processing of the Coronavirus Replicase Nonstructural Protein 14 Exonuclease Is Not Required for Virus Replication but Alters RNA Synthesis and Viral Fitness

Coronaviruses (CoVs) initiate replication by translation of the positive-sense RNA genome into the replicase polyproteins connecting 16 nonstructural protein domains (nsp1-16), which are subsequently processed by viral proteases to yield mature nsp. For the betacoronavirus murine hepatitis virus (MHV), total inhibition of translation or proteolytic processing of replicase polyproteins results in rapid cessation of RNA synthesis. The nsp5-3CLpro (Mpro) processes nsps7-16, which assemble into functional replication-transcription complexes (RTCs), including the enzymatic nsp12-RdRp and nsp14-exoribonuclease (ExoN)/N7-methyltransferase. The nsp14-ExoN activity mediates RNA-dependent RNA proofreading, high-fidelity RNA synthesis, and replication. To date, the solved partial RTC structures, biochemistry, and models use or assume completely processed, mature nsp. Here, we demonstrate that in MHV, engineered deletion of the cleavage sites between nsp13-14 and nsp14-15 allowed recovery of replication-competent virus. Compared to wild-type (WT) MHV, the nsp13-14 and nsp14-15 cleavage deletion mutants demonstrated delayed replication kinetics, impaired genome production, altered abundance and patterns of recombination, and impaired competitive fitness. Further, the nsp13-14 and nsp14-15 mutant viruses demonstrated mutation frequencies that were significantly higher than with the WT. The results demonstrate that cleavage of nsp13-14 or nsp14-15 is not required for MHV viability and that functions of the RTC/nsp14-ExoN are impaired when assembled with noncleaved intermediates. These data will inform future genetic, structural, biochemical, and modeling studies of coronavirus RTCs and nsp 13, 14, and 15 and may reveal new approaches for inhibition or attenuation of CoV infection.

IMPORTANCE Coronavirus replication requires proteolytic maturation of the nonstructural replicase proteins to form the replication-transcription complex. Coronavirus replication-transcription complex models assume mature subunits; however, mechanisms of coronavirus maturation and replicase complex formation have yet to be defined. Here, we show that for the coronavirus murine hepatitis virus, cleavage between the nonstructural replicase proteins nsp13-14 and nsp14-15 is not required for replication but does alter RNA synthesis and recombination. These results shed new light on the requirements for coronavirus maturation and replication-transcription complex assembly, and they may reveal novel therapeutic targets and strategies for attenuation.

Setomimycin as a potential molecule for COVID‑19 target: in silico approach and in vitro validation

Abstract

COVID-19 pandemic caused by the SARS-CoV-2 virus has led to a worldwide crisis. In view of emerging variants time to time, there is a pressing need of effective COVID-19 therapeutics. Setomimycin, a rare tetrahydroanthracene antibiotic, remained unexplored for its therapeutic uses. Herein, we report our investigations on the potential of setomimycin as COVID-19 therapeutic. Pure setomimycin was isolated from Streptomyces sp. strain RA-WS2 from NW Himalayan region followed by establishing in silico as well as in vitro anti-SARS-CoV-2 property of the compound against SARS-CoV-2 main protease (M^pro). It was found that the compound targets M^pro enzyme with an IC₅₀ value of 12.02 ± 0.046 μM. The molecular docking study revealed that the compound targets Glu166 residue of M^pro enzyme, hence preventing dimerization of SARS-CoV-2 M^pro monomer. Additionally, the compound also exhibited anti-inflammatory and anti-oxidant property, suggesting that setomimycin may be a viable option for application against COVID-19 infections.

Graphical abstract

An Overview of Antiviral Peptides and Rational Biodesign Considerations

Viral diseases have contributed significantly to worldwide morbidity and mortality throughout history. Despite the existence of therapeutic treatments for many viral infections, antiviral resistance and the threat posed by novel viruses highlight the need for an increased number of effective therapeutics. In addition to small molecule drugs and biologics, antimicrobial peptides (AMPs) represent an emerging class of potential antiviral therapeutics. While AMPs have traditionally been regarded in the context of their antibacterial activities, many AMPs are now known to be antiviral. These antiviral peptides (AVPs) have been shown to target and perturb viral membrane envelopes and inhibit various stages of the viral life cycle, from preattachment inhibition through viral release from infected host cells. Rational design of AMPs has also proven effective in identifying highly active and specific peptides and can aid in the discovery of lead peptides with high therapeutic selectivity. In this review, we highlight AVPs with strong antiviral activity largely curated from a publicly available AMP database. We then compile the sequences present in our AVP database to generate structural predictions of generic AVP motifs. Finally, we cover the rational design approaches available for AVPs taking into account approaches currently used for the rational design of AMPs.

Investigation of Cu metal nanoparticles with different morphologies to inhibit SARS-CoV-2 main protease and spike glycoprotein using Molecular Docking and Dynamics Simulation

Nowadays, considering the spread of the coronavirus as a global threat, scientific research on this virus through simulation has been increasing. In this study, effect of Cu nanocluster on prevention and control of disease transmission was examined using molecular docking and molecular dynamics simulation studies on the SARS-CoV-2 main protease and spike glycoprotein. The cytotoxicity of different shapes of copper NPs and resonance changes of their surface plasmons on inactivation of the coronavirus was examined in order to control replication of coronavirus through copper NPs, active site of protease and spike glycoprotein. The simulations results showed that interactions of SARS-CoV-2 main protease and spike glycoprotein target and cylindrical and conical copper NPs ligands were more efficient than spherical copper NPs.

Coronavirus enzyme inhibitors-experimentally proven natural compounds from plants

Coronavirus disease (COVID-19) can cause critical conditions that require efficient therapeutics. Several medicines are derived from plants, and researchers are seeking natural compounds to ameliorate the symptoms of COVID-19. Viral enzymes are popular targets of antiviral medicines; the genome of coronaviruses encodes several enzymes, including RNA-dependent RNA polymerase and viral proteases. Various screening systems have been developed to identify potential inhibitors. In this review, we describe the natural compounds that have been shown to exert inhibitory effects on coronavirus enzymes. Although computer-aided molecular structural studies have predicted several antiviral compound candidates, the current review focuses on experimentally proven natural compounds.

A new glimpse on the active site of SARS-CoV-2 3CLpro, coupled with drug repurposing study

Coronavirus disease 2019 (COVID-19) is caused by novel severe acute respiratory syndrome coronavirus (SARS-CoV-2). Its main protease, 3C-like protease (3CLpro), is an attractive target for drug design, due to its importance in virus replication. The analysis of the radial distribution function of 159 3CLpro structures reveals a high similarity index. A study of the catalytic pocket of 3CLpro with bound inhibitors reveals that the influence of the inhibitors is local, perturbing dominantly only residues in the active pocket. A machine learning based model with high predictive ability against SARS-CoV-2 3CLpro is designed and validated. The model is used to perform a drug-repurposing study, with the main aim to identify existing drugs with the highest 3CLpro inhibition power. Among antiviral agents, lopinavir, idoxuridine, paritaprevir, and favipiravir showed the highest inhibition potential. Enzyme - ligand interactions as a key ingredient for successful drug design.

Viral proteases: Structure, mechanism and inhibition

Viral proteases are diverse in structure, oligomeric state, catalytic mechanism, and substrate specificity. This chapter focuses on proteases from viruses that are relevant to human health: human immunodeficiency virus subtype 1 (HIV-1), hepatitis C (HCV), human T-cell leukemia virus type 1 (HTLV-1), flaviviruses, enteroviruses, and coronaviruses. The proteases of HIV-1 and HCV have been successfully targeted for therapeutics, with picomolar FDA-approved drugs currently used in the clinic. The proteases of HTLV-1 and the other virus families remain emerging therapeutic targets at different stages of the drug development process. This chapter provides an overview of the current knowledge on viral protease structure, mechanism, substrate recognition, and inhibition. Particular focus is placed on recent advances in understanding the molecular basis of diverse substrate recognition and resistance, which is essential toward designing novel protease inhibitors as antivirals.

Deep-learning in situ classification of HIV-1 virion morphology

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Efficient classifier capable of overcoming inherent problems of small-data training sets.

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Automated detection and classification of HIV-1 particle morphology from transmission electron micrographs.

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Three orders of magnitude speed increase in data processing with negligible loss in accuracy.

Transmission electron microscopy (TEM) has a multitude of uses in biomedical imaging due to its ability to discern ultrastructure morphology at the nanometer scale. Through its ability to directly visualize virus particles, TEM has for several decades been an invaluable tool in the virologist’s toolbox. As applied to HIV-1 research, TEM is critical to evaluate activities of inhibitors that block the maturation and morphogenesis steps of the virus lifecycle. However, both the preparation and analysis of TEM micrographs requires time consuming manual labor. Through the dedicated use of computer vision frameworks and machine learning techniques, we have developed a convolutional neural network backbone of a two-stage Region Based Convolutional Neural Network (RCNN) capable of identifying, segmenting and classifying HIV-1 virions at different stages of maturation and morphogenesis. Our results outperformed common RCNN backbones, achieving 80.0% mean Average Precision on a diverse set of micrographs comprising different experimental samples and magnifications. We expect that this tool will be of interest to a broad range of researchers.

The proximal proteome of 17 SARS-CoV-2 proteins links to disrupted antiviral signaling and host translation

Viral proteins localize within subcellular compartments to subvert host machinery and promote pathogenesis. To study SARS-CoV-2 biology, we generated an atlas of 2422 human proteins vicinal to 17 SARS-CoV-2 viral proteins using proximity proteomics. This identified viral proteins at specific intracellular locations, such as association of accessary proteins with intracellular membranes, and projected SARS-CoV-2 impacts on innate immune signaling, ER-Golgi transport, and protein translation. It identified viral protein adjacency to specific host proteins whose regulatory variants are linked to COVID-19 severity, including the TRIM4 interferon signaling regulator which was found proximal to the SARS-CoV-2 M protein. Viral NSP1 protein adjacency to the EIF3 complex was associated with inhibited host protein translation whereas ORF6 localization with MAVS was associated with inhibited RIG-I 2CARD-mediated IFNB1 promoter activation. Quantitative proteomics identified candidate host targets for the NSP5 protease, with specific functional cleavage sequences in host proteins CWC22 and FANCD2. This data resource identifies host factors proximal to viral proteins in living human cells and nominates pathogenic mechanisms employed by SARS-CoV-2.

SARS-CoV-2 is the latest pathogenic coronavirus to emerge as a public health threat. We create a database of proximal host proteins to 17 SARS-CoV-2 viral proteins. We validate that NSP1 is proximal to the EIF3 translation initiation complex and is a potent inhibitor of translation. We also identify ORF6 antagonism of RNA-mediate innate immune signaling. We produce a database of potential host targets of the viral protease NSP5, and create a fluorescence-based assay to screen cleavage of peptide sequences. We believe that this data will be useful for identifying roles for many of the uncharacterized SARS-CoV-2 proteins and provide insights into the pathogenicity of new or emerging coronaviruses.

Gag-Gag Interactions Are Insufficient to Fully Stabilize and Order the Immature HIV Gag Lattice

Immature HIV virions harbor a lattice of Gag molecules with significant ordering in CA-NTD, CA-CTD and SP1 regions. This ordering plays a major role during HIV maturation. To test the condition in which the Gag lattice forms in vivo, we assembled virus like particles (VLPs) by expressing only HIV Gag in mammalian cells. Here we show that these VLPs incorporate a similar number of Gag molecules compared to immature HIV virions. However, within these VLPs, Gag molecules diffuse with a pseudo-diffusion rate of 10 nm2/s, this pseudo-diffusion is abrogated in the presence of melittin and is sensitive to mutations within the SP1 region. Using cryotomography, we show that unlike immature HIV virions, in the Gag lattice of VLPs the CA-CTD and SP1 regions are significantly less ordered. Our observations suggest that within immature HIV virions, other viral factors in addition to Gag, contribute to ordering in the CA-CTD and SP1 regions.

Viral 3CLpro as a Target for Antiviral Intervention Using Milk-Derived Bioactive Peptides

Viruses of the picornavirus-like supercluster mainly achieve cleavage of polyproteins into mature proteins through viral 3-chymotrypsin proteases (3C^pro) or 3-chymotrypsin-like proteases (3CL^pro). Due to the essential role in processing viral polyproteins, 3C^pro/3CL^pro is a drug target for treating viral infections. The 3CL^pro is considered the main protease (M^pro) of coronaviruses. In the current study, the SARS-CoV-2 M^pro inhibitory activity of di- and tri-peptides (DTPs) resulted from the proteolysis of bovine milk proteins was evaluated. A set of 326 DTPs were obtained from virtual digestion of bovine milk major proteins. The resulted DTPs were screened using molecular docking. Twenty peptides (P1–P20) showed the best binding energies (ΔG_b <  − 7.0 kcal/mol). Among these 20 peptides, the top five ligands, namely P1 (RVY), P3 (QSW), P17 (DAY), P18 (QSA), and P20 (RNA), based on the highest binding affinity and the highest number of interactions with residues in the active site of M^pro were selected for further characterization by ADME/Tox analyses. For further validation of our results, molecular dynamics simulation was carried out for P3 as one of the most favorable candidates for up to 100 ns. In comparison to N3, a peptidomimetic control inhibitor, high stability was observed as supported by the calculated binding energy of the M^pro-P3 complex (− 59.48 ± 4.87 kcal/mol). Strong interactions between P3 and the M^pro active site, including four major hydrogen bonds to HIS41, ASN142, GLU166, GLN189 residues, and many hydrophobic interactions from which the interaction with CYS145 as a catalytic residue is worth mentioning. Conclusively, milk-derived bioactive peptides, especially the top five selected peptides P1, P3, P17, P18, and P20, show promise as an antiviral lead compound.

Human herpesvirus-encoded MicroRNA in host-pathogen interaction

Human herpesviruses (HHV) are ubiquitous, linear dsDNA viruses that establish lifelong latency, disrupted by sporadic reactivation. HHV have evolved diverse ingenious mechanisms to evade robust host defenses. Incorporation of unique stem loop sequences that generate viral microRNAs (v-miRs) exemplifies one such evolutionary adaptation in HHV. These noncoding RNAs can control cellular and viral transcriptomes highlighting their ability in shaping host-HHV interactions. We summarize recent developments in functional characterization of HHV-encoded miRNAs in shaping the outcome of host-pathogen interaction. Non-immunogenic dissemination of v-miRs through exosomes confer added advantage to HHV in incessant modulation of host microenvironment. This review delineates the mechanistic role of v-miRs in facilitating viral persistence and tropism by targeting genes associated with cellular (apoptosis, angiogenesis, cell migration, etc.) and viral life cycle (latency, lytic and reactivation). Burgeoning evidences indicate plausible association of v-miRs in various immune-mediated diseases (nasopharyngeal carcinoma, neurological disorders, periodontal diseases, etc.) and herpesvirus-related malignancies indicating their broad-spectrum impact on host cellular pathways. We propose to exploit tisssue and systemic levels of v-miRs as diagnostic and prognostic markers for cancers and immune-mediated diseases. Therapeutic targeting of v-miRs will advance the promising outcomes of preclinical discoveries to bedside application.

Role of Iron Chelation and Protease Inhibition of Natural Products on COVID-19 Infection

Although the epidemic caused by SARS-CoV-2 callings for international attention to develop new effective therapeutics, no specific protocol is yet available, leaving patients to rely on general and supportive therapies. A range of respiratory diseases, including pulmonary fibrosis, have been associated with higher iron levels that may promote the course of viral infection. Recent studies have demonstrated that some natural components could act as the first barrier against viral injury by affecting iron metabolism. Moreover, a few recent studies have proposed the combination of protease inhibitors for therapeutic use against SARS-CoV-2 infection, highlighting the role of viral protease in virus infectivity. In this regard, this review focuses on the analysis, through literature and docking studies, of a number of natural products able to counteract SARS-CoV-2 infection, acting both as iron chelators and protease inhibitors.

Genetic variation analyses indicate conserved SARS-CoV-2-host interaction and varied genetic adaptation in immune response factors in modern human evolution

Coronavirus disease 2019 (COVID‐19), caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), is a pandemic as of early 2020. Upon infection, SARS‐CoV‐2 attaches to its receptor, that is, angiotensin‐converting enzyme 2 (ACE2), on the surface of host cells and is then internalized into host cells via enzymatic machineries. This subsequently stimulates immune response factors. Since the host immune response and severity of COVID‐19 vary among individuals, genetic risk factors for severe COVID‐19 cases have been investigated. Our research group recently conducted a survey of genetic variants among SARS‐CoV‐2‐interacting molecules across populations, noting near absence of difference in allele frequency spectrum between populations in these genes. Recent genome‐wide association studies have identified genetic risk factors for severe COVID‐19 cases in a segment of chromosome 3 that involves six genes encoding three immune‐regulatory chemokine receptors and another three molecules. The risk haplotype seemed to be inherited from Neanderthals, suggesting genetic adaptation against pathogens in modern human evolution. Therefore, SARS‐CoV‐2 uses highly conserved molecules as its virion interaction, whereas its immune response appears to be genetically biased in individuals to some extent. We herein review the molecular process of SARS‐CoV‐2 infection as well as our further survey of genetic variants of its related immune effectors. We also discuss aspects of modern human evolution.

Proteolytic Cleavages in the VEGF Family: Generating Diversity among Angiogenic VEGFs, Essential for the Activation of Lymphangiogenic VEGFs

Simple Summary

Vascular endothelial growth factors (VEGFs) regulate the growth of blood and lymphatic vessels. Some of them induce the growth of blood vessels, and others the growth of lymphatic vessels. Blocking VEGF-A is used today to treat several types of cancer (“antiangiogenic therapy”). However, in other diseases, we would like to increase the activity of VEGFs. For example, VEGF-A could generate new blood vessels to protect from heart disease, and VEGF-C could generate new lymphatics to counteract lymphedema. Clinical trials are testing the latter concept at the moment. Because VEGF-C and VEGF-D are produced as inactive precursors, we propose that novel drugs could also target the enzymatic activation of VEGF-C and VEGF-D. However, because of the delicate balance between too much and too little vascular growth, a detailed understanding of the activation of the VEGFs is needed before such concepts can be converted into safe and efficacious therapies.

Abstract

Specific proteolytic cleavages turn on, modify, or turn off the activity of vascular endothelial growth factors (VEGFs). Proteolysis is most prominent among the lymph­angiogenic VEGF-C and VEGF-D, which are synthesized as precursors that need to undergo enzymatic removal of their C- and N-terminal propeptides before they can activate their receptors. At least five different proteases mediate the activating cleavage of VEGF-C: plasmin, ADAMTS3, prostate-specific antigen, cathepsin D, and thrombin. All of these proteases except for ADAMTS3 can also activate VEGF-D. Processing by different proteases results in distinct forms of the “mature” growth factors, which differ in affinity and receptor activation potential. The “default” VEGF-C-activating enzyme ADAMTS3 does not activate VEGF-D, and therefore, VEGF-C and VEGF-D do function in different contexts. VEGF-C itself is also regulated in different contexts by distinct proteases. During embryonic development, ADAMTS3 activates VEGF-C. The other activating proteases are likely important for non-developmental lymphangiogenesis during, e.g., tissue regeneration, inflammation, immune response, and pathological tumor-associated lymphangiogenesis. The better we understand these events at the molecular level, the greater our chances of developing successful therapies targeting VEGF-C and VEGF-D for diseases involving the lymphatics such as lymphedema or cancer.

The proximal proteome of 17 SARS-CoV-2 proteins links to disrupted antiviral signaling and host translation

Viral proteins localize within subcellular compartments to subvert host machinery and promote pathogenesis. To study SARS-CoV-2 biology, we generated an atlas of 2422 human proteins vicinal to 17 SARS-CoV-2 viral proteins using proximity proteomics. This identified viral proteins at specific intracellular locations, such as association of accessary proteins with intracellular membranes, and projected SARS-CoV-2 impacts on innate immune signaling, ER-Golgi transport, and protein translation. It identified viral protein adjacency to specific host proteins whose regulatory variants are linked to COVID-19 severity, including the TRIM4 interferon signaling regulator which was found proximal to the SARS-CoV-2 M protein. Viral NSP1 protein adjacency to the EIF3 complex was associated with inhibited host protein translation whereas ORF6 localization with MAVS was associated with inhibited RIG-I 2CARD-mediated IFNB1 promoter activation. Quantitative proteomics identified candidate host targets for the NSP5 protease, with specific functional cleavage sequences in host proteins CWC22 and FANCD2. This data resource identifies host factors proximal to viral proteins in living human cells and nominates pathogenic mechanisms employed by SARS-CoV-2.

Author Summary

SARS-CoV-2 is the latest pathogenic coronavirus to emerge as a public health threat. We create a database of proximal host proteins to 17 SARS-CoV-2 viral proteins. We validate that NSP1 is proximal to the EIF3 translation initiation complex and is a potent inhibitor of translation. We also identify ORF6 antagonism of RNA-mediate innate immune signaling. We produce a database of potential host targets of the viral protease NSP5, and create a fluorescence-based assay to screen cleavage of peptide sequences. We believe that this data will be useful for identifying roles for many of the uncharacterized SARS-CoV-2 proteins and provide insights into the pathogenicity of new or emerging coronaviruses.

Inhibitor binding influences the protonation states of histidines in SARS-CoV-2 main protease

The main protease (M^pro) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an attractive target for antiviral therapeutics. Recently, many high-resolution apo and inhibitor-bound structures of M^pro, a cysteine protease, have been determined, facilitating structure-based drug design. M^pro plays a central role in the viral life cycle by catalyzing the cleavage of SARS-CoV-2 polyproteins. In addition to the catalytic dyad His41–Cys145, M^pro contains multiple histidines including His163, His164, and His172. The protonation states of these histidines and the catalytic nucleophile Cys145 have been debated in previous studies of SARS-CoV M^pro, but have yet to be investigated for SARS-CoV-2. In this work we have used molecular dynamics simulations to determine the structural stability of SARS-CoV-2 M^pro as a function of the protonation assignments for these residues. We simulated both the apo and inhibitor-bound enzyme and found that the conformational stability of the binding site, bound inhibitors, and the hydrogen bond networks of M^pro are highly sensitive to these assignments. Additionally, the two inhibitors studied, the peptidomimetic N3 and an α-ketoamide, display distinct His41/His164 protonation-state-dependent stabilities. While the apo and the N3-bound systems favored N_δ (HD) and N_ϵ (HE) protonation of His41 and His164, respectively, the α-ketoamide was not stably bound in this state. Our results illustrate the importance of using appropriate histidine protonation states to accurately model the structure and dynamics of SARS-CoV-2 M^pro in both the apo and inhibitor-bound states, a necessary prerequisite for drug-design efforts.

The main protease (M^pro) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an attractive target for antiviral therapeutics.

Current Synthetic Routes to Peptidyl Mono-Fluoromethyl Ketones (FMKs) and Their Applications

Peptidyl mono-fluoromethyl ketones (FMKs) are a class of biologically active molecules that show potential as both protease inhibitors for the treatment of a range of diseases and as chemical probes for the interrogation of cellular processes. This review describes the current solid- and solution-phase routes employed for the synthesis of peptidyl mono-FMKs. In addition, it provides a brief overview of some of the key applications of FMKs in the fields of chemical biology and medicinal chemistry.

SARS-CoV-2: a new dimension to our understanding of coronaviruses

Coronaviruses have marked their significant emergence since the twenty-first century with the outbreaks of three out of the seven existing human coronaviruses, including the severe acute respiratory syndrome coronavirus (SARS-CoV) in 2003, Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 2019. These viruses have not only acquired large-scale transmission during their specified outbreak period, but cases of MERS-CoV still remain active, although there is only limited transmission. While, on the other hand, SARS-CoV-2 continues to remain a rising threat to global public health. The recent novel coronavirus, SARS-CoV-2, responsible for the ongoing coronavirus disease 2019 (COVID-19), emerged during December 2019 in Wuhan, China, and has repeatedly raised questions about its characteristic variability. Despite belonging to the same family, SARS-CoV-2 has proven to be quite difficult to control and contain in terms of transmissibility, leading to around 19.8 million reported cases and more than 730,000 deaths of individuals worldwide. Here, we discuss how SARS-CoV-2 differs from its two other related human coronaviruses in terms of genome composition, site of infection, and transmissibility, among several other notable aspects—all indicating to the possibility that it is these variations in addition to other unknowns that are contributing to this virus’ differing deadly pattern.

Potential COVID-19 papain-like protease PLpro inhibitors: repurposing FDA-approved drugs

Using the crystal structure of SARS-CoV-2 papain-like protease (PLpro) as a template, we developed a pharmacophore model of functional centers of the PLpro inhibitor-binding pocket. With this model, we conducted data mining of the conformational database of FDA-approved drugs. This search identified 147 compounds that can be potential inhibitors of SARS-CoV-2 PLpro. The conformations of these compounds underwent 3D fingerprint similarity clusterization, followed by docking of possible conformers to the binding pocket of PLpro. Docking of random compounds to the binding pocket of protease was also done for comparison. Free energies of the docking interaction for the selected compounds were lower than for random compounds. The drug list obtained includes inhibitors of HIV, hepatitis C, and cytomegalovirus (CMV), as well as a set of drugs that have demonstrated some activity in MERS, SARS-CoV, and SARS-CoV-2 therapy. We recommend testing of the selected compounds for treatment of COVID-19.

Inhibitor binding influences the protonation states of histidines in SARS-CoV-2 main protease

The main protease (M ^pro ) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an attractive target for antiviral therapeutics. Recently, many high-resolution apo and inhibitor-bound structures of M ^pro , a cysteine protease, have been determined, facilitating structure-based drug design. M ^pro plays a central role in the viral life cycle by catalyzing the cleavage of SARS-CoV-2 polyproteins. In addition to the catalytic dyad His41-Cys145, M ^pro contains multiple histidines including His163, His164, and His172. The protonation states of these histidines and the catalytic nu-cleophile Cys145 have been debated in previous studies of SARS-CoV M ^pro , but have yet to be investigated for SARS-CoV-2. In this work we have used molecular dynamics simulations to determine the structural stability of SARS-CoV-2 M ^pro as a function of the protonation assignments for these residues. We simulated both the apo and inhibitor-bound enzyme and found that the conformational stability of the binding site, bound inhibitors, and the hydrogen bond networks of M ^pro are highly sensitive to these assignments. Additionally, the two inhibitors studied, the peptidomimetic N3 and an α -ketoamide, display distinct His41/His164 protonation-state-dependent stabilities. While the apo and the N3-bound systems favored N _δ (HD) and N _ϵ (HE) protonation of His41 and His164, respectively, the α -ketoamide was not stably bound in this state. Our results illustrate the importance of using appropriate histidine protonation states to accurately model the structure and dynamics of SARS-CoV-2 M ^pro in both the apo and inhibitor-bound states, a necessary prerequisite for drug-design efforts.

SARS-CoV-2/COVID-19 and advances in developing potential therapeutics and vaccines to counter this emerging pandemic

A novel coronavirus (SARS-CoV-2), causing an emerging coronavirus disease (COVID-19), first detected in Wuhan City, Hubei Province, China, which has taken a catastrophic turn with high toll rates in China and subsequently spreading across the globe. The rapid spread of this virus to more than 210 countries while affecting more than 25 million people and causing more than 843,000 human deaths, it has resulted in a pandemic situation in the world. The SARS-CoV-2 virus belongs to the genus Betacoronavirus, like MERS-CoV and SARS-CoV, all of which originated in bats. It is highly contagious, causing symptoms like fever, dyspnea, asthenia and pneumonia, thrombocytopenia, and the severely infected patients succumb to the disease. Coronaviruses (CoVs) among all known RNA viruses have the largest genomes ranging from 26 to 32 kb in length. Extensive research has been conducted to understand the molecular basis of the SARS-CoV-2 infection and evolution, develop effective therapeutics, antiviral drugs, and vaccines, and to design rapid and confirmatory viral diagnostics as well as adopt appropriate prevention and control strategies. To date, August 30, 2020, no effective, proven therapeutic antibodies or specific drugs, and vaccines have turned up. In this review article, we describe the underlying molecular organization and phylogenetic analysis of the coronaviruses, including the SARS-CoV-2, and recent advances in diagnosis and vaccine development in brief and focusing mainly on developing potential therapeutic options that can be explored to manage this pandemic virus infection, which would help in valid countering of COVID-19.

Monoclonal antibody as a potential anti-COVID-19

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Human neutralizing antibodies can block COVID-19 infection.

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Most monoclonal antibodies inhibit binding S protein to ACE2 receptor.

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Researchers are trying to develop treatments based on antibodies to block and/or neutralize SARS-CoV-2.

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The genetic and structural similarity of the virus to SARS-CoV helps for designing new methods for treatment of COVID-19.

Coronavirus disease 2019 (COVID-19) is expanding rapidly, which made it as one of top priorities for scientists to develop novel treatment strategies. Researchers are racing to develop treatments based on antibodies to block and/or neutralize the coronavirus in affected patients. Initially, the genetic and structural similarity of the virus to severe acute respiratory syndrome coronavirus (SARS-CoV) created the potential for understanding disease pathogenesis. Researchers have published reports of specific monoclonal antibodies against to COVID-19 (B38, H4, 47D11) and hope that this method is effective. As well as studies on patients who are plasma therapy, the patient's condition shows improvement. The evidence for these studies is very promising and demonstrates the potential of monoclonal antibody therapy as a therapeutic approach and prevention of covid-19 infection.

New Insights of Emerging SARS-CoV-2: Epidemiology, Etiology, Clinical Features, Clinical Treatment, and Prevention

Since the first reports that the novel coronavirus was showing human-to-human transmission characteristics and asymptomatic cases, the number of patients with associated pneumonia has continued to rise and the epidemic has grown. It now threatens the health and lives of people across the world. The governments of many countries have attached great importance to the prevention of SARS-CoV-2, via research into the etiology and epidemiology of this newly emerged disease. Clinical signs, treatment, and prevention characteristics of the novel coronavirus pneumonia have been receiving attention worldwide, especially from medical personnel. However, owing to the different experimental methods, sample sizes, sample sources, and research perspectives of various studies, results have been inconsistent, or relate to an isolated aspect of the virus or the disease it causes. Currently, systematic summary data on the novel coronavirus are limited. This review combines experimental and clinical evidence into a systematic analysis and summary of the current progress of research into SARS-CoV-2, from multiple perspectives, with the aim of gaining a better overall understanding of the disease. Our report provides important information for current clinicians, for the prevention and treatment of COVID-19 pneumonia.

Therapeutic strategies in an outbreak scenario to treat the novel coronavirus originating in Wuhan, China

A novel coronavirus (2019-nCoV) originating in Wuhan, China presents a potential respiratory viral pandemic to the world population. Current efforts are focused on containment and quarantine of infected individuals. Ultimately, the outbreak could be controlled with a protective vaccine to prevent 2019-nCoV infection. While vaccine research should be pursued intensely, there exists today no therapy to treat 2019-nCoV upon infection, despite an urgent need to find options to help these patients and preclude potential death. Herein, I review the potential options to treat 2019-nCoV in patients, with an emphasis on the necessity for speed and timeliness in developing new and effective therapies in this outbreak. I consider the options of drug repurposing, developing neutralizing monoclonal antibody therapy, and an oligonucleotide strategy targeting the viral RNA genome, emphasizing the promise and pitfalls of these approaches. Finally, I advocate for the fastest strategy to develop a treatment now, which could be resistant to any mutations the virus may have in the future. The proposal is a biologic that blocks 2019-nCoV entry using a soluble version of the viral receptor, angiotensin-converting enzyme 2 (ACE2), fused to an immunoglobulin Fc domain (ACE2-Fc), providing a neutralizing antibody with maximal breath to avoid any viral escape, while also helping to recruit the immune system to build lasting immunity. The ACE2-Fc therapy would also supplement decreased ACE2 levels in the lungs during infection, thereby directly treating acute respiratory distress pathophysiology as a third mechanism of action. The sequence of the ACE2-Fc protein is provided to investigators, allowing its possible use in recombinant protein expression systems to start producing drug today to treat patients under compassionate use, while formal clinical trials are later undertaken. Such a treatment could help infected patients before a protective vaccine is developed and widely available in the coming months to year(s).

Therapeutic strategies in an outbreak scenario to treat the novel coronavirus originating in Wuhan, China

A novel coronavirus (2019-nCoV) originating in Wuhan, China presents a potential respiratory viral pandemic to the world population. Current efforts are focused on containment and quarantine of infected individuals. Ultimately, the outbreak could be controlled with a protective vaccine to prevent 2019-nCoV infection. While vaccine research should be pursued intensely, there exists today no therapy to treat 2019-nCoV upon infection, despite an urgent need to find options to help these patients and preclude potential death. Herein, I review the potential options to treat 2019-nCoV in patients, with an emphasis on the necessity for speed and timeliness in developing new and effective therapies in this outbreak. I consider the options of drug repurposing, developing neutralizing monoclonal antibody therapy, and an oligonucleotide strategy targeting the viral RNA genome, emphasizing the promise and pitfalls of these approaches. Finally, I advocate for the fastest strategy to develop a treatment now, which could be resistant to any mutations the virus may have in the future. The proposal is a biologic that blocks 2019-nCoV entry using a soluble version of the viral receptor, angiotensin-converting enzyme 2 (ACE2), fused to an immunoglobulin Fc domain, providing a neutralizing antibody with maximal breath to avoid any viral escape, while also helping to recruit the immune system to build lasting immunity. The sequence of the ACE2-Fc protein is provided to investigators, allowing its possible use in recombinant protein expression systems to start producing drug today to treat patients under compassionate use, while formal clinical trials are later undertaken. Such a treatment could help infected patients before a protective vaccine is developed and widely available in the coming months to year(s).

Dominant Negative MA-CA Fusion Protein Is Incorporated into HIV-1 Cores and Inhibits Nuclear Entry of Viral Preintegration Complexes

Particle maturation is a critical step in the HIV-1 replication cycle that requires proteolytic cleavage of the Gag polyprotein into its constitutive proteins: the matrix (MA), capsid (CA), nucleocapsid (NC), and p6 proteins. The accurate and efficient cleavage of Gag is essential for virion infectivity; inhibitors of the viral protease are potent antivirals, and substitutions in Gag that prevent its cleavage result in reduced HIV-1 infectivity. In a previous study, a mutation inhibiting cleavage at the MA-CA junction was observed to potently inhibit virus infection: incorporation of small amounts of uncleaved MA-CA protein into HIV-1 particles inhibited infectivity by ∼95%, and the resulting viral particles exhibited aberrant capsids. Here we report a detailed mechanistic analysis of HIV-1 particles bearing uncleaved MA-CA protein. We show that the particles contain stable cores and can efficiently saturate host restriction by TRIMCyp in target cells. We further show that MA-CA associates with CA in particles without detectably affecting the formation of intermolecular CA interfaces. Incorporation of MA-CA did not markedly affect reverse transcription in infected cells, but nuclear entry was impaired and integration targeting was altered. Additionally, results from mutational analysis of Gag revealed that membrane-binding elements of MA contribute to the antiviral activity of uncleaved MA-CA protein. Our results suggest that small amounts of partially processed Gag subunits coassemble with CA during virion maturation, resulting in impaired capsid functions.IMPORTANCE To become infectious, newly formed HIV-1 particles undergo a process of maturation in which the viral polyproteins are cleaved into smaller components. A previous study demonstrated that inclusion of even small quantities of an uncleavable mutant Gag polyprotein results in a strong reduction in virus infectivity. Here we show that the mechanism of transdominant inhibition by uncleavable Gag involves inhibition of nuclear entry and alteration of viral integration sites. Additionally, the results of mutational analysis suggest that the membrane-binding activity of Gag is a major requirement for the antiviral activity. These results further define the antiviral mechanism of uncleavable Gag, which may be useful for exploiting this effect to develop new antivirals.

Synthetic routes and structure-activity relationships (SAR) of anti-HIV agents: A key review

The worldwide increase of AIDS, an epidemic infection in constant development has an essential and still requires potent antiretroviral chemotherapeutic agents for reducing the integer of deaths caused by HIV. Thus, there is an urgent need for new anti-HIV drug candidates with increased strength, new targets, superior pharmacokinetic properties, and compact side effects. From this viewpoint, we first review present strategies of anti-HIV drug innovation and the synthesis of heterocyclic or natural compound as anti-HIV agents for facilitating the development of more influential and successful anti-HIV agents.

GII.4 Norovirus Protease Shows pH-Sensitive Proteolysis with a Unique Arg-His Pairing in the Catalytic Site

Human noroviruses (NoVs) are the main cause of epidemic and sporadic gastroenteritis. Phylogenetically, noroviruses are divided into seven genogroups, with each divided into multiple genotypes. NoVs belonging to genogroup II and genotype 4 (GII.4) are globally most prevalent. Genetic diversity among the NoVs and the periodic emergence of novel strains present a challenge for the development of vaccines and antivirals to treat NoV infection. NoV protease is essential for viral replication and is an attractive target for the development of antivirals. The available structure of GI.1 protease provided a basis for the design of inhibitors targeting the active site of the protease. These inhibitors, although potent against the GI proteases, poorly inhibit the GII proteases, for which structural information is lacking. To elucidate the structural basis for this difference in the inhibitor efficiency, we determined the crystal structure of a GII.4 protease. The structure revealed significant changes in the S2 substrate-binding pocket, making it noticeably smaller, and in the active site, with the catalytic triad residues showing conformational changes. Furthermore, a conserved arginine is found inserted into the active site, interacting with the catalytic histidine and restricting substrate/inhibitor access to the S2 pocket. This interaction alters the relationships between the catalytic residues and may allow for a pH-dependent regulation of protease activity. The changes we observed in the GII.4 protease structure may explain the reduced potency of the GI-specific inhibitors against the GII protease and therefore must be taken into account when designing broadly cross-reactive antivirals against NoVs.IMPORTANCE Human noroviruses (NoVs) cause sporadic and epidemic gastroenteritis worldwide. They are divided into seven genogroups (GI to GVII), with each genogroup further divided into several genotypes. Human NoVs belonging to genogroup II and genotype 4 (GII.4) are the most prevalent. Currently, there are no vaccines or antiviral drugs available for NoV infection. The protease encoded by NoV is considered a valuable target because of its essential role in replication. NoV protease structures have only been determined for the GI genogroup. We show here that the structure of the GII.4 protease exhibits several significant changes from GI proteases, including a unique pairing of an arginine with the catalytic histidine that makes the proteolytic activity of GII.4 protease pH sensitive. A comparative analysis of NoV protease structures may provide a rational framework for structure-based drug design of broadly cross-reactive inhibitors targeting NoVs.

Targeting HIV-1 Protease Autoprocessing for High-throughput Drug Discovery and Drug Resistance Assessment

HIV-1 protease autoprocessing liberates the free mature protease from its Gag-Pol polyprotein precursor through a series of highly regulated autoproteolysis reactions. Herein, we report the development and validation (Z' ≥ 0.50) of a cell-based functional assay for high-throughput screening (HTS) of autoprocessing inhibitors using fusion precursors in combination with AlphaLISA (amplified luminescent proximity homogeneous assay ELISA). Through pilot screening of a collection of 130 known protease inhibitors, the AlphaLISA assay confirmed all 11 HIV protease inhibitors in the library capable of suppressing precursor autoprocessing at low micromolar concentrations. Meanwhile, other protease inhibitors had no impact on precursor autoprocessing. We next conducted HTS of ~23,000 compounds but found no positive hits. Such high selectivity is advantageous for large-scale HTS campaigns and as anticipated based on assay design because a positive hit needs simultaneously to be nontoxic, cell permeable, and inhibiting precursor autoprocessing. Furthermore, AlphaLISA quantification of fusion precursors carrying mutations known to cause resistance to HIV protease inhibitors faithfully recapitulated the reported resistance, suggesting that precursor autoprocessing is a critical step contributing to drug resistance. Taken together, this reported AlphaLISA platform will provide a useful tool for drug discovery targeting HIV-1 protease autoprocessing and for quantification of PI resistance.

Hydroxychloroquine Inhibits Zika Virus NS2B-NS3 Protease

Zika virus is a mosquito-transmitted flavivirus that causes devastating fetal outcomes in the context of maternal infection during pregnancy. An important target for drugs combatting Zika virus pathogenicity is NS2B-NS3 protease, which plays an essential role in hydrolysis and maturation of the flavivirus polyprotein. We identify hydroxychloroquine, a drug that already has approved uses in pregnancy, as a possible inhibitor of NS2B-NS3 protease by using a Food and Drug Administration-approved drug library, molecular docking, and molecular dynamics simulations. Further, to gain insight into its inhibitory potential toward NS2B-NS3 protease, we performed enzyme kinetic studies, which revealed that hydroxychloroquine inhibits protease activity with an inhibition constant (K i) of 92.34 ± 11.91 μM. Additionally, hydroxychloroquine significantly decreases Zika virus infection in placental cells.

Plant Viral Proteases: Beyond the Role of Peptide Cutters

Almost half of known plant viral species rely on proteolytic cleavages as key co- and post-translational modifications throughout their infection cycle. Most of these viruses encode their own endopeptidases, proteases with high substrate specificity that internally cleave large polyprotein precursors for the release of functional sub-units. Processing of the polyprotein, however, is not an all-or-nothing process in which endopeptidases act as simple peptide cutters. On the contrary, spatial-temporal modulation of these polyprotein cleavage events is crucial for a successful viral infection. In this way, the processing of the polyprotein coordinates viral replication, assembly and movement, and has significant impact on pathogen fitness and virulence. In this mini-review, we give an overview of plant viral proteases emphasizing their importance during viral infections and the varied functionalities that result from their proteolytic activities.

Therapeutic Approaches for Zika Virus Infection of the Nervous System

Zika virus has spread rapidly in the Americas and has caused devastation of human populations affected in these regions. The virus causes teratogenic effects involving the nervous system, and in adults and children can cause a neuropathy similar to Guillain-Barré syndrome, an anterior myelitis, or, rarely, an encephalitis. While major efforts have been undertaken to control mosquito populations that spread the virus and to develop a vaccine, drug development that directly targets the virus in an infected individual to prevent or treat the neurological manifestations is necessary. Rational and targeted drug development is possible since the viral life cycle and the structure of the key viral proteins are now well understood. While several groups have identified therapeutic candidates, their approaches differ in the types of screening processes and viral assays used. Animal studies are available for only a few compounds. Here we provide an exhaustive review and compare each of the classes of drugs discovered, the methods used for drug discovery, and their potential use in humans for the prevention or treatment of neurological complications of Zika virus infection.

Structure-Activity Relationship Study of QL47: A Broad-Spectrum Antiviral Agent

Here we report the structure-activity relationship (SAR) investigations of QL-XII-47 (QL47), a compound that possesses broad-spectrum antiviral activity against dengue virus and other RNA viruses. A medicinal chemistry campaign initiated from QL47, a previously reported covalent BTK inhibitor, to derive YKL-04-085, which is devoid of any kinase activity when screened against a panel of 468 kinases and with improved pharmacokinetic properties. Both QL47 and YKL-04-085 are potent inhibitors of viral translation and exhibit cellular antiviral activity at 35-fold lower concentrations relative to inhibition of host-cell proliferation.

Proteolytic activity assayed by subcellular localization switching of a substrate

An approach to assay proteolytic activity in vivo by altering the subcellular localization of a labelled substrate was demonstrated. The assay included a protein shuttling between different cellular compartments and a site-specific recombinant protease. The shuttle protein used was the human immunodeficiency virus type 1 (HIV-1) Rev protein tandemly fused to the enhanced green fluorescent protein (EGFP) and the red fluorescent protein (RFP), while the protease was the site-specific protease VP24 from the herpes simplex virus type 1 (HSV-1). The fluorescent proteins in the Rev fusion protein were separated by a cleavage site specific for the VP24 protease. When co-expressed in COS-7 cells proteolysis was observed by fluorescence microscopy as a shift from a predominantly cytoplasmic localization of the fusion protein RevEGFP to a nuclear localization while the RFP part of the fusion protein remained in the cytoplasm. The cleavage of the fusion protein by VP24 was confirmed by Western blot analysis. The activity of VP24, when tagged N-terminally by the Myc-epitope, was found to be comparable to VP24. These results demonstrates that the activity and localization of a recombinantly expressed protease can be assessed by protease-mediated cleavage of fusion proteins containing a specific protease cleavage site.

A novel cell-based assay to measure activity of Venezuelan equine encephalitis virus nsP2 protease

The encephalitic alphaviruses encode nsP2 protease (nsP2pro), which because of its vital role in virus replication, represents an attractive target for therapeutic intervention. To facilitate the discovery of nsP2 inhibitors we have developed a novel assay for quantitative measurement of nsP2pro activity in a cell-based format. The assay is based on a substrate fusion protein consisting of eGFP and Gaussia luciferase (Gluc) linked together by a small peptide containing a VEEV nsp2pro cleavage sequence. The expression of the substrate protein in cells along with recombinant nsP2pro results in cleavage of the substrate protein resulting in extracellular release of free Gluc. The Gluc activity in supernatants corresponds to intracellular nsP2pro-mediated substrate cleavage; thus, providing a simple and convenient way to quantify nsP2pro activity. Here, we demonstrate potential utility of the assay in identification of nsP2pro inhibitors, as well as in investigations related to molecular characterization of nsP2pro.

Retroviral proteases and their roles in virion maturation

Proteolytic processing of viral polyproteins is essential for retrovirus infectivity. Retroviral proteases (PR) become activated during or after assembly of the immature, non-infectious virion. They cleave viral polyproteins at specific sites, inducing major structural rearrangements termed maturation. Maturation converts retroviral enzymes into their functional form, transforms the immature shell into a metastable state primed for early replication events, and enhances viral entry competence. Not only cleavage at all PR recognition sites, but also an ordered sequence of cleavages is crucial. Proteolysis is tightly regulated, but the triggering mechanisms and kinetics and pathway of morphological transitions remain enigmatic. Here, we outline PR structures and substrate specificities focusing on HIV PR as a therapeutic target. We discuss design and clinical success of HIV PR inhibitors, as well as resistance development towards these drugs. Finally, we summarize data elucidating the role of proteolysis in maturation and highlight unsolved questions regarding retroviral maturation.

A review on recent developments of indole-containing antiviral agents

Indole represents one of the most important privileged scaffolds in drug discovery. Indole derivatives have the unique property of mimicking the structure of peptides and to bind reversibly to enzymes, which provide tremendous opportunities to discover novel drugs with different modes of action. There are seven indole-containing commercial drugs in the Top-200 Best Selling Drugs by US Retail Sales in 2012. There are also an amazing number of approved indole-containing drugs in the market as well as compounds currently going through different clinical phases or registration statuses. This review focused on the recent development of indole derivatives as antiviral agents with the following objectives: 1) To present one of the most comprehensive listings of indole antiviral agents, drugs on market or compounds in clinical trials; 2) To focus on recent developments of indole compounds (including natural products) and their antiviral activities, summarize the structure property, hoping to inspire new and even more creative approaches; 3) To offer perspectives on how indole scaffolds as a privileged structure might be exploited in the future.

Induced maturation of human immunodeficiency virus

HIV-1 assembles at the plasma membrane of virus-producing cells as an immature, noninfectious particle. Processing of the Gag and Gag-Pol polyproteins by the viral protease (PR) activates the viral enzymes and results in dramatic structural rearrangements within the virion--termed maturation--that are a prerequisite for infectivity. Despite its fundamental importance for viral replication, little is currently known about the regulation of proteolysis and about the dynamics and structural intermediates of maturation. This is due mainly to the fact that HIV-1 release and maturation occur asynchronously both at the level of individual cells and at the level of particle release from a single cell. Here, we report a method to synchronize HIV-1 proteolysis in vitro based on protease inhibitor (PI) washout from purified immature virions, thereby temporally uncoupling virus assembly and maturation. Drug washout resulted in the induction of proteolysis with cleavage efficiencies correlating with the off-rate of the respective PR-PI complex. Proteolysis of Gag was nearly complete and yielded the correct products with an optimal half-life (t(1/2)) of ~5 h, but viral infectivity was not recovered. Failure to gain infectivity following PI washout may be explained by the observed formation of aberrant viral capsids and/or by pronounced defects in processing of the reverse transcriptase (RT) heterodimer associated with a lack of RT activity. Based on our results, we hypothesize that both the polyprotein processing dynamics and the tight temporal coupling of immature particle assembly and PR activation are essential for correct polyprotein processing and morphological maturation and thus for HIV-1 infectivity.

IMPORTANCE

Cleavage of the Gag and Gag-Pol HIV-1 polyproteins into their functional subunits by the viral protease activates the viral enzymes and causes major structural rearrangements essential for HIV-1 infectivity. This proteolytic maturation occurs concomitant with virus release, and investigation of its dynamics is hampered by the fact that virus populations in tissue culture contain particles at all stages of assembly and maturation. Here, we developed an inhibitor washout strategy to synchronize activation of protease in wild-type virus. We demonstrated that nearly complete Gag processing and resolution of the immature virus architecture are accomplished under optimized conditions. Nevertheless, most of the resulting particles displayed irregular morphologies, Gag-Pol processing was not faithfully reconstituted, and infectivity was not recovered. These data show that HIV-1 maturation is sensitive to the dynamics of processing and also that a tight temporal link between virus assembly and PR activation is required for correct polyprotein processing.

Design and synthesis of highly potent HIV-1 protease inhibitors with novel isosorbide-derived P2 ligands

The design, synthesis, and biological evaluation of a series of six HIV-1 protease inhibitors incorporating isosorbide moiety as novel P2 ligands are described. All the compounds are very potent HIV-1 protease inhibitors with IC50 values in the nanomolar or picomolar ranges (0.05-0.43 nM). Molecular docking studies revealed the formation of an extensive hydrogen-bonding network between the inhibitor and the active site. Particularly, the isosorbide-derived P2 ligand is involved in strong hydrogen bonding interactions with the backbone atoms.

Homology modeling and virtual screening for antagonists of protease from yellow head virus

Yellow head virus (YHV) is one of the causative agents of shrimp viral disease. The prevention of YHV infection in shrimp has been developed by various methods, but it is still insufficient to protect the mass mortality in shrimp. New approaches for the antiviral drug development for viral infection have been focused on the inhibition of several potent viral enzymes, and thus the YHV protease is one of the interesting targets for developing antiviral drugs according to the pivotal roles of the enzyme in an early stage of viral propagation. In this study, a theoretical modeling of the YHV protease was constructed based on the folds of several known crystal structures of other viral proteases, and was subsequently used as a target for virtual screening—molecular docking against approximately 1364 NCI structurally diversity compounds. A complex between the protease and the hit compounds was investigated for intermolecular interactions by molecular dynamics simulations. Five best predicted compounds (NSC122819, NSC345647, NSC319990, NSC50650, and NSC5069) were tested against bacterial expressed YHV. The NSC122819 showed the best inhibitory characteristic among the candidates, while others showed more than 50 % of inhibition in the assay condition. These compounds could potentially be inhibitors for curing YHV infection.