Infected Host Cells Research Articles

VE607 stabilizes SARS-CoV-2 Spike in the “RBD-up” conformation and inhibits viral entry

SummarySARS-CoV-2 infection of host cells starts by binding the Spike glycoprotein (S) to the ACE2 receptor. The S-ACE2 interaction is a potential target for therapies against COVID-19 as demonstrated by the development of immunotherapies blocking this interaction. VE607 — a commercially available compound composed of three stereoisomers — was described as an inhibitor of SARS-CoV-1. Here, we show that VE607 broadly inhibits pseudoviral particles bearing the Spike from major VOCs (D614G, Alpha, Beta, Gamma, Delta, Omicron – BA.1, and BA.2) as well as authentic SARS-CoV-2 at low micromolar concentrations. In silico docking, mutational analysis, and smFRET revealed that VE607 binds to the receptor binding domain (RBD)-ACE2 interface and stabilizes RBD in its “up” conformation. Prophylactic treatment with VE607 did not prevent SARS-CoV-2-induced mortality in K18-hACE2 mice, but it did reduce viral replication in the lungs by 37-fold. Thus, VE607 is an interesting lead for drug development for the treatment of SARS-CoV-2 infection.

RNA Thermometer-coordinated Assembly of the Yersinia Injectisome

The type III secretion system (T3SS) is indispensable for successful host cell infection by many Gram-negative pathogens. The molecular syringe delivers effector proteins that suppress the host immune response. Synthesis of T3SS components in Yersinia pseudotuberculosis relies on host body temperature, which induces the RNA thermometer (RNAT)-controlled translation of lcrF coding for a virulence master regulator that activates transcription of the T3SS regulon. The assembly of the secretion machinery follows a strict coordinated succession referred to as outside-in assembly, in which the membrane ring complex and the export apparatus represent the nucleation points. Two components essential for the initial assembly are YscJ and YscT. While YscJ connects the membrane ring complex with the export apparatus in the inner membrane, YscT is required for a functional export apparatus. Previous transcriptome-wide RNA structuromics data suggested the presence of unique intercistronic RNATs upstream of yscJ and yscT. Here, we show by reporter gene fusions that both upstream regions confer translational control. Moreover, we demonstrate the temperature-induced opening of the Shine-Dalgarno region, which facilitates ribosome binding, by in vitro structure probing and toeprinting methods. Rationally designed thermostable RNAT variants of the yscJ and yscT thermometers confirmed their physiological relevance with respect to T3SS assembly and host infection. Since we have shown in a recent study that YopN, the gatekeeper of type III secretion, also is under RNAT control, it appears that the synthesis, assembly and functionality of the Yersinia T3S machinery is coordinated by RNA-based temperature sensors at multiple levels.

Integrated Analysis of miRNA-mRNA Expression in Mink Lung Epithelial Cells Infected With Canine Distemper Virus

Canine distemper (CD) caused by canine distemper virus (CDV) is one of the major infectious diseases in minks, bringing serious economic losses to the mink breeding industry. By an integrated analysis of microRNA (miRNA)-messenger RNA (mRNA), the present study analyzed the changes in the mink transcriptome upon CDV infection in mink lung epithelial cells (Mv. l. Lu cells) for the first time. A total of 4,734 differentially expressed mRNAs (2,691 upregulated and 2,043 downregulated) with |log2(FoldChange) |>1 and P-adj<0.05 and 181 differentially expressed miRNAs (152 upregulated and 29 downregulated) with |log2(FoldChange) |>2 and P-adj<0.05 were identified. Gene Ontology (GO) enrichment indicated that differentially expressed genes (DEGs) were associated with various biological processes and molecular function, such as response to stimulus, cell communication, signaling, cytokine activity, transmembrane signaling receptor activity and signaling receptor activity. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of the combination of miRNA and mRNA was done for immune and inflammatory responses, such as Janus kinase (JAK)-signal transducer and activator (STAT) signaling pathway and nuclear factor (NF)-kappa B signaling pathway. The enrichment analysis of target mRNA of differentially expressed miRNA revealed that mir-140-5p and mir-378-12 targeted corresponding genes to regulate NF-kappa B signaling pathway. JAK-STAT signaling pathway could be modulated by mir-425-2, mir-139-4, mir-140-6, mir-145-3, mir-140-5p and mir-204-2. This study compared the influence of miRNA-mRNA expression in Mv. l. Lu cells before and after CDV infection by integrated analysis of miRNA-mRNA and analyzed the complex network interaction between virus and host cells. The results can help understand the molecular mechanism of the natural immune response induced by CDV infection in host cells.

Identification of MYH9 Key Domain Involved in the Entry of PRRSV Into Permissive Cells.

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen that causes huge losses economically to the pig industry worldwide. Previous research suggested that receptor dependence is necessary for PRRSV infection. MYH9 and CD163 are indispensable for PRRSV entry into a porcine alveolar macrophage. In the present study, human MYH9 (hMYH9) and mouse MYH9 (mMYH9), similar to swine MYH9, could also accelerate PRRSV infection in pCD163-mediated cell lines. Knockdown of MYH9 activity using the specific small interfering RNA or inhibitor (blebbistatin) concomitantly decreased PRRSV infection. C-terminal fragment of MYH9 (PRA) proteins from different mammalian species contains a conserved binding domain (aa1676-1791) for PRRSV binding, since the recombinant MYH91676−1791protein could inhibit the PRRSV infection significantly. Furthermore, the specific polyclonal antibody of MYH91676−1791 could block PRRSV infection in host cells. These data strongly supported that MYH9, a very important cofactor, participated in PRRSV entry into target cells, which may facilitate the development of a new therapeutic agent to control PRRSV infection.

Plasmodium falciparum Molecular Chaperones: Guardians of the Malaria Parasite Proteome and Renovators of the Host Proteome.

Plasmodium falciparum is a unicellular protozoan parasite and causative agent of the most severe form of malaria in humans. The malaria parasite has had to develop sophisticated mechanisms to preserve its proteome under the changing stressful conditions it confronts, particularly when it invades host erythrocytes. Heat shock proteins, especially those that function as molecular chaperones, play a key role in protein homeostasis (proteostasis) of P. falciparum. Soon after invading erythrocytes, the malaria parasite exports a large number of proteins including chaperones, which are responsible for remodeling the infected erythrocyte to enable its survival and pathogenesis. The infected host cell has parasite-resident and erythrocyte-resident chaperones, which appear to play a vital role in the folding and functioning of P. falciparum proteins and potentially host proteins. This review critiques the current understanding of how the major chaperones, particularly the Hsp70 and Hsp40 (or J domain proteins, JDPs) families, contribute to proteostasis of the malaria parasite-infected erythrocytes.

DWV 3C Protease Uncovers the Diverse Catalytic Triad in Insect RNA Viruses.

ABSTRACTDeformed wing virus (DWV) is the most prevalent Iflavirus that is infecting honey bees worldwide. However, the mechanisms of its infection and replication in host cells are poorly understood. In this study, we analyzed the structure and function of DWV 3C protease (3Cpro), which is necessary for the cleavage of the polyprotein to synthesize mature viral proteins. Thus, it is one of the nonstructural viral proteins essential for the replication. We found that the 3Cpros of DWV and picornaviruses share common enzymatic properties, including sensitivity to the same inhibitors, such as rupintrivir. The predicted structure of DWV 3Cpro by AlphaFold2, the predicted rupintrivir binding domain, and the protease activities of mutant proteins revealed that it has a Cys-His-Asn catalytic triad. Moreover, 3Cpros of other Iflaviruses and Dicistrovirus appear to contain Asn, Ser, Asp, or Glu as the third residue of the catalytic triad, suggesting diversity in insect RNA viruses. Both precursor 3Cpro with RNA-dependent RNA polymerase and mature 3Cpro are present in DWV-infected cells, suggesting that they may have different enzymatic properties and functions. DWV 3Cpro is the first 3Cpro characterized among insect RNA viruses, and our study uncovered both the common and unique characteristics among 3Cpros of Picornavirales. Furthermore, it would be possible to use the specific inhibitors of DWV 3Cpro to control DWV infection in honey bees in future.IMPORTANCE The number of managed honey bee (Apis mellifera) colonies has considerably declined in many developed countries in the recent years. Deformed wing virus (DWV) vectored by the mites is the major threat to honey bee colonies and health. To give insight into the mechanism of DWV replication in the host cells, we studied the structure–function relationship of 3C protease (3Cpro), which is necessary to cleave a viral polyprotein at the specific sites to produce the mature proteins. We found that the overall structure, some inhibitors, and processing of 3Cpro are shared between Picornavirales; however, there is diversity in the catalytic triad. DWV 3Cpro is the first viral protease characterized among insect RNA viruses and reveals the evolutionary history of 3Cpro among Picornavirales. Furthermore, DWV 3Cpro inhibitors identified in our study could also be applied to control DWV in honey bees in future.

Comparing Influenza Virus Biology for Understanding Influenza D Virus.

The newest type of influenza virus, influenza D virus (IDV), was isolated in 2011. IDV circulates in several animal species worldwide, causing mild respiratory illness in its natural hosts. Importantly, IDV does not cause clinical disease in humans and does not spread easily from person to person. Here, we review what is known about the host–pathogen interactions that may limit IDV illness. We focus on early immune interactions between the virus and infected host cells in our summary of what is known about IDV pathogenesis. This work establishes a foundation for future research into IDV infection and immunity in mammalian hosts.

Non-canonical nematode endogenous retroviruses resulting from RNA virus glycoprotein gene capture by a metavirus.

Reverse-transcribing retroviruses exist as horizontally transmitted infectious agents or vertically transmitted endogenous retroviruses (ERVs) resident in eukaryotic genomes, and they are phylogenetically related to the long terminal repeat (LTR) class of retrotransposons. ERVs and retrotransposons are often distinguished only by the presence or absence of a gene encoding the envelope glycoprotein (env). Endogenous elements of the virus family Metaviridae include the insect-restricted Errantivirus genus of ERVs, for which some members possess env, and the pan-eukaryotic Metavirus genus that lacks an envelope glycoprotein gene. Here we report a novel Nematoda endogenous retrovirus (NERV) clade with core retroviral genes arranged uniquely as a continuous gag-env-pro-pol ORF. Reverse transcriptase sequences were phylogenetically related to metaviruses, but envelope glycoprotein sequences resembled those of the Nyamiviridae and Chrysoviridae RNA virus families, suggesting env gene capture during host cell infection by an RNA virus. NERVs were monophyletic, restricted to the nematode subclass Chromadoria, and included additional ORFs for a small hypothetical protein or a large Upf1-like RNA-dependent AAA-ATPase/helicase indicative of viral transduction of a host gene. Provirus LTR identity, low copy number, ORF integrity and segregation of three loci in Meloidogyne incognita, taken together with detection of NERV transcriptional activity, support potential infectivity of NERVs, along with their recent emergence and integration. Altogether, NERVs constitute a new and distinct Metaviridae lineage demonstrating retroviral evolution through sequential heterologous gene capture events.

Ampicillin Treatment of Intracellular Listeria monocytogenes Triggers Formation of Persistent, Drug-Resistant L-Form Cells.

Listeria monocytogenes is an opportunistic intracellular pathogen causing an infection termed listeriosis. Despite the low incidence of listeriosis, the high mortality rate in individuals at risk makes this bacterium one of the most dangerous foodborne pathogens. Reports about a relapse of infection after antibiotic treatment suggest that the bacteria may be able to evade antibiotic treatment and persist as a dormant, antibiotic-tolerant subpopulation. In this study, we observed intracellular generation of antibiotic-resistant L-forms of Listeria monocytogenes following Ampicillin treatment of Listeria monocytogenes infected cells. Detection and identification of intracellular Listeria L-forms was performed by a combination of fluorescence in-situ hybridization and confocal laser scanning microscopy. Using micromanipulation, it was possible to isolate single intracellular L-form cells that following transfer into fresh medium gave rise to pure cultures. In conclusion, the results obtained here provide strong evidence that antibiotic treatment of infected host cells can induce the formation of L-forms from intracellular Listeria monocytogenes. Furthermore, our results suggest that intracellular L-forms persist inside host cells and that they represent viable bacteria, which are still able to grow and proliferate.

The Evolutionary Dance between Innate Host Antiviral Pathways and SARS-CoV-2.

Compared to what we knew at the start of the SARS-CoV-2 global pandemic, our understanding of the interplay between the interferon signaling pathway and SARS-CoV-2 infection has dramatically increased. Innate antiviral strategies range from the direct inhibition of viral components to reprograming the host’s own metabolic pathways to block viral infection. SARS-CoV-2 has also evolved to exploit diverse tactics to overcome immune barriers and successfully infect host cells. Herein, we review the current knowledge of the innate immune signaling pathways triggered by SARS-CoV-2 with a focus on the type I interferon response, as well as the mechanisms by which SARS-CoV-2 impairs those defenses.

Development of humanized ACE2 mouse and rat models for COVID‐19 research

To date (17 November 2021), there has been more than 254 million confirmed cases of COVID‐19, and more than 5 million death globally (World Health Organization. https://covid19.who.int/). The virus causing COVID‐19 is called Severe Acute Respiratory Syndrome Coronavirus 2 (SARS‐CoV‐2). SARS‐CoV‐2 infects host cells by the binding of its spike protein to the cellular surface protein angiotensin‐converting enzyme 2 (ACE2). The predicted 29 amino acid residues of ACE2 that interact with SARS‐CoV‐2 spike protein receptor binding domain (RBD) vary between human ACE2 and mouse or rat ACE2. Therefore, wildtype mice and rats show lower SARS‐CoV‐2 infection rate and mild symptoms compared to what is seen in humans. Small animal models that recapitulate human COVID‐19 disease are urgently needed for better understanding the transmission and therapeutic measurement. Currently, scientists use either mouse‐adapted SAS‐CoV‐2 (SAS‐CoV‐2 MA) models or random transgenic mouse models that artificially express human ACE2 under the control of cytokeratin 18 promoter or a constitutive promoter. SAS‐CoV‐2 MA may not completely reflect all aspects of the original human‐tropic SAS‐CoV‐2 and the current transgenic human ACE2 mouse models typically have high mortality rate caused by neuroinvasion and encephalitis due to very high human ACE2 expression. To overcome these limitations, we have developed humanized ACE2 mouse and rat models using CRISPR‐Cas9. Specifically, we inserted a ~3kb human ACE2 cDNA cassette into the mouse and rat Ace2 gene loci to ensure that human ACE2 expression is under the control of rodent Ace2 promoter and regulatory elements, while simultaneously disabling the rodent Ace2 gene. To accomplish this, CRISPR gRNAs targeting close to the translation initiation site of Ace2 were screened in cultured mouse and rat cells. Then CRISPR/Cas9 complex and donor DNA were subsequently microinjected into one‐cell stage embryos which were subsequently implanted into pseudo pregnant females. Resulting pups were screened for correct knockin by junction PCR and insert PCR, and the PCR products were Sanger sequenced. Targeted Locus Amplification (TLA) further confirmed the integration sites and transgene sequence. RT‐qPCR and Western blot analysis data showed that, in our models, human ACE2 is expressed in tissues expressing endogenous Ace2 (such as lung, kidney, and GI tract), while rodent endogenous Ace2 is absent from these tissues. Further breeding data indicated that both hemizygous and homozygous humanized ACE2 animals appear to be normal and fertile. Most importantly, animals displayed symptoms after infection with SARS‐CoV‐2. In summary, these data suggest that our humanized ACE2 models can be valuable for COVID‐19 research.

SARS-CoV-2 uses different entry routes to infect host cells

SARS-CoV-2 uses different entry routes to infect host cells

Channel catfish virus entry into host cells via clathrin-mediated endocytosis

Channel catfish virus (CCV), an important member of the family Alloherpesviridae, causes a lethal infection in channel catfish. As with most animal viruses, the initial step of infection by CCV is entry into host cells, which is also a promising antiviral target for CCV disease. This study investigated the mechanism of host cell invasion by CCV using a series of biochemical inhibitor assays in channel catfish cells. CCV infection in host cells was does-dependently inhibited when cells were treated with endosomal acidification inhibitors (5 μM chloroquine, 50 nM bafilomycin A1, and 1 mM ammonium chloride) and hypertonic medium (50 mM sucrose) , which suggests that CCV invades host cells in a manner dependent on low-pH and the endocytic pathway. Moreover, when the cells were pretreated with inhibitors of clathrin-mediated endocytosis, including chlorpromazine (2 μM) and dynasore (50 μM), the CCV infection in the host cells was strongly inhibited. In contrast, the destruction of cellular cholesterol by methyl-β-cyclodextrin and nystatin and inhibition of macropinocytosis had no effect on viral entry. Altogether, these findings indicate that CCV infects host cells via clathrin-mediated endocytosis in a low-pH-dependent manner, suggesting that this CCV entry pathway offers an antiviral target against CCV disease.

Covalent binding of human two-domain CD4 to an HIV-1 subtype C SOSIP.664 trimer modulates its structural dynamics

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) mediates host cell infection by binding to the cellular receptor CD4. Recombinant Env bound to CD4 has been explored for its potential as an HIV vaccine immunogen as receptor binding exposes otherwise shielded, conserved functional sites. Previous preclinical studies showed an interchain disulphide linkage facilitated between Env and 2dCD4S60C generates an immunogenic complex that elicits potent, broadly neutralizing antibodies (bNAbs) against clinically relevant HIV-1. This study investigated conformational dynamics of 2dCD4WT and 2dCD4S60C bound to an HIV–1C SOSIP.664 Env trimer using hydrogen-deuterium exchange mass spectrometry. The Env:2dCD4S60C complex maintains key contact residues required for MHCII and Env/gp120 binding and the residues encompassing Ibalizumab's epitope. Important residues remaining anchored, with an increased flexibility in surrounding regions, evidenced by the higher exchange seen in flanking residues compared to Env:2dCD4WT. While changes in Env:2dCD4S60C dynamics in domain 1 were moderate, domain 2 exhibited greater variation. Lack of stability-inducing H-bonds in these allosteric sites suggest the improved immunogenicity of Env:2dCD4S60C result from exposed CD4 residues providing diverse/novel antigenic targets for the development of potent, broadly neutralizing Ibalizumab-like antibodies.

Neuropsychiatric and behavioral disorders in patients with COVID-19

The article discusses the epidemiological, etiopathogenetic, clinical, and diagnostic aspects of central nervous system damage in COVID-19. The SARS-CoV-2 virus can pass through physiological barriers and reach the bloodstream or lymph, spreading in the central nervous system of an infected person, infect host cells through many metabolic pathways, which determines the features of the clinical picture of neuropsychiatric and behavioral disorders in the patient, represented by a spectrum of phenotypes (syndromes), one way or another associated with the main infectious process. As a rule, this is a clinical diagnosis based on the results of a comprehensive examination of a patient with COVID-19. Direct virus-induced damage, immune dysfunction, excessive inflammation, thrombophilia/hypercoagulation, cytokine and metabolic imbalance, and autoimmune changes that are pathogenetic mechanisms in developing neuropsychiatric diseases in patients with COVID-19 are described. The review substantiates the need for a comprehensive examination, an interdisciplinary approach, and multicomponent therapy of patients with a new coronavirus infection. Dynamic monitoring of COVID-19 convalescents will allow us to objectively talk about the risk of developing long-term consequences of SARS-CoV-2 infection, and maintaining clinical alertness regarding the possible development of neurological symptoms in most patients with the new COVID-19 coronavirus infection will help to provide effective assistance both in the acute period of the disease and during recovery, recovery and comprehensive rehabilitation: neurological, psychological, musculoskeletal.

PdpC, a Type Six Secretion System Substrate, is Required for Erythrocyte Invasion in Francisella tularensis LVS

Francisella tularensis is an intracellular pathogen and the causative agent of tularemia. The F. tularensis type six secretion system (T6SS) is required for phagolysosomal escape and invasion of erythrocytes. An effector of the T6SS, PdpC, is required for phagosomal escape and we wanted to test if PdpC was also required for erythrocyte invasion. We constructed a pdpC-null mutant in the live vaccine strain, F. tularensis LVS. The pdpC-null strain is required for invasion of both human and sheep erythrocytes and reintroduction of a copy of pdpC, in trans, rescues this phenotype. Differential Immuno-Fluorescence Microscopy (DIFM) showed that the pdpC-null strain is affected in attachment as well as invasion. Further, a fluorescently labelled pdpC-null strain of F. tularensis LVS was unable to proliferate in THP-1 human peripheral blood monocyte cells. Finally, we constructed a fluorescent fusion of pdpC to emgfp and the resulting PdpC-EmGFP fusion protein localizes as discrete foci in a subset of broth cultured F. tularensis LVS cells. Our results confirm previous observations that PdpC is required for infection and virulence in phagocytic host cells and are the first description of an effector of the Type Six Secretion System that is required for erythrocyte invasion. The pdpC-emgfp strain will be a useful tool to further characterize the role of PdpC in both macrophage infection and red blood cell invasion. (This research was made possible by NASA West Virginia Space Grant Consortium Training Grant #NNX15A101H and by NIH Grant P20GM103434 to the West Virginia IDeA Network for Biomedical Research Excellence).

Analysis of the Effectiveness of Masks at Blocking Bacterial Particulates.

In light of the recent pandemic, this study was conducted to determine the effectiveness of masks stopping bacterial particles. The Centers for Disease Control and Prevention (CDC) has recommended a multitude of varying face masks that are said to protect you and others from the spread of COVID-19 and other air-borne microbes. The main goal of this research was to test recommended masks and determine if they are as protective as everyone acknowledges them to be.&#x0D; To evaluate the masks, multiple mathematical formulas were used to accurately imitate the average human cough. These calculations were used to build a machine that would expel air and a microbial solution through a mask. A bacterial sample was used to determine the effectiveness of microbe containment by the various masks due to the ability to obtain penetration measurements without the need of host cell infection. The machine constructed to mimic a human cough consists of a pressure regulator, “cough chamber”, and a mouth nozzle. The concentration of bacterial solution was factored into the amount of particulate that is expelled after an average cough. The standardized bacteria-containing cough solution was then dispersed through the mouth nozzle and a mask. Any particulate that passed through the mask was collected on a nutrient agar plate, which was used to quantify the number of microbial particles that breached the mask.&#x0D; Preliminary data indicates that there is a difference in the effectiveness of the masks and some masks do not appear to be as effective as they are advertised to be. This calls into question the validity of the CDC’s recommendations for masks effective at preventing the transmission of air-borne microbes.

The Interplay Between COVID-19 and Cardiovascular Disease

Introduction: The emergence of the global COVID-19 pandemic caused by the severe acute respiratory syndrome coronavirus, SARS-CoV-2, has created a substantial burden on healthcare systems worldwide. The systemic impacts of COVID-19 infection are severe and broad in their implications, and the cardiovascular system is no exception. Discussion: Patients with a history of cardiovascular disease are at an increased risk for hospitalization and mortality, and COVID-19 infection has now been demonstrated to initiate acute, but serious, episodes of cardiovascular events such as stroke. Considering the rapid spread of COVID-19 across the globe and the inability of healthcare systems to address and adequately respond to the pandemic, therein lies an increased need for understanding the interplay between COVID-19 infection and cardiovascular disease. SARS-CoV-2 relies on binding the angiotensin-converting enzyme-2 (ACE2) receptor to infect host cells, with ACE2 representing a critical regulator of blood pressure homeostasis and proper cardiovascular functioning. Conclusion: Identifying the exact role of ACE2 in COVID-19 infection will have major implications for understanding the disease; therefore, here we have reviewed ACE2’s involvement in the pathogenesis of COVID-19 infection and the resulting end-organ damage. In addition, we have summarized how COVID-19 affects cardiovascular physiology, and how COVID-19 infection can manifest in acute cardiovascular events. Finally, we examine why patients with cardiovascular disease are at an increased risk of succumbing to COVID-19 and what the long-term cardiovascular implications of COVID-19 infection could mean. Relevance: This paper discusses the cardiovascular consequences of the global COVID-19 pandemic.

Synthetic carbohydrate-binding agents neutralize SARS-CoV-2 by inhibiting binding of the spike protein to ACE2

SummaryDeveloping strategies against the SARS-CoV-2 is currently a main research subject. SARS-CoV-2 infects host cells by binding to human ACE2 receptors. Both, virus and ACE2, are highly glycosylated, and exploiting glycans of the SARS-CoV-2 envelope as binding sites for ACE2 represents a virus strategy for attacking the human host. We report here that a family of mannose-binding synthetic carbohydrate-binding agents (CBAs) inhibits SARS-CoV-2 infection, showing broad neutralizing activity vs. several variants of the spike protein. Preliminary tests indicated that the investigated CBAs interact with the spike protein rather than with ACE2. For a lead compound (IDS060), which has been selected among others for its lack of cytotoxicity, evidence of binding to the RBD of the spike protein has been found by NMR experiments, while competitive binding assays in the presence of IDS060 showed inhibition of binding of RBD to hACE2, although neutralizing activity was also observed with variants showing reduced or depleted binding.

Heterologous expression of scFv fragment against Vairimorpha (Nosema) ceranae hexokinase in Sf9 cell culture inhibits microsporidia intracellular growth

Secretion of hexokinase (HK) by microsporidia into infected cells suggests an important role for this enzyme for the intracellular development of parasites. To verify whether the expression of HK-specific antibodies in the host cell cytoplasm can suppress the growth of microsporidia, we constructed an immune library of recombinant scFv fragments against the enzyme of the honey bee pathogen Vairimorpha (Nosema) ceranae (VcHK) with a representativeness of about 5 million bacterial transformants. Two variants of VcHK-specific recombinant antibodies were selected by library panning and expressed in lepidopteran Sf9 cell line. Infecting of cells expressing two selected and control scFv fragments with V. ceranae spores was followed by their cultivation for 4 days. Analysis of parasite β-tubulin as well as spore wall protein SWP32 transcripts in infected cultures by reverse transcription PCR and real-time qPCR showed (1) V. ceranae growth in cells heterologous to bee pathogens, (2) its inhibition by one of the selected VcHK-specific recombinant antibodies. The latter result once again emphasizes an important role of microsporidia hexokinases in their relationships with infected host cells and suggests further focusing on the mechanisms of such suppression, as well as on the search for new V. ceranae - inhibiting scFv fragments.