scholarly journals Structural Insights into the Human Astrovirus Capsid

Viruses ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 821
Author(s):  
Matthew Ykema ◽  
Yizhi J. Tao
Keyword(s):  
Host Cell ◽  
Neutralizing Antibodies ◽  
Structural Changes ◽  
Inflammatory Diseases ◽  
Host Cells ◽  
Viral Capsid ◽  
Target Cells ◽  
New Host ◽  
Wide Range ◽  
Protease Cleavage Sites

Astroviruses (AstVs) are non-enveloped, positive single-stranded RNA viruses that cause a wide range of inflammatory diseases in mammalian and avian hosts. The T = 3 viral capsid is unique in its ability to infect host cells in a process driven by host proteases. Intercellular protease cleavages allow for viral egress from a cell, while extracellular cleavages allow for the virus to enter a new host cell to initiate infection. High-resolution models of the capsid core indicate a large, exposed region enriched with protease cleavage sites. The virus spike protein allows for binding to target cells and is the major target for naturally occurring and engineered neutralizing antibodies. During maturation, the capsid goes through significant structural changes including the loss of many surface spikes. The capsid interacts with host membranes during the virus life cycle at multiple stages such as assembly, host cell entry and exit. This review will cover recent findings and insights related to the structure of the capsid and its function. Further understanding of the viral capsid structure and maturation process can contribute to new vaccines, gastric therapeutics, and viral engineering applications.

scholarly journals A surrogate virus neutralization test to quantify antibody-mediated inhibition of SARS-CoV-2 in finger stick dried blood spot samples

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Amelia E. Sancilio ◽  
Richard T. D’Aquila ◽  
Elizabeth M. McNally ◽  
Matthew P. Velez ◽  
Michael G. Ison ◽  
...  
Keyword(s):  
Neutralizing Antibodies ◽  
Venous Blood ◽  
Host Cells ◽  
Dried Blood Spot ◽  
Blood Collection ◽  
Widespread Application ◽  
Live Virus ◽  
Dilution Series ◽  
Wide Range ◽  
Blood Spot

AbstractThe spike protein of SARS-CoV-2 engages the human angiotensin-converting enzyme 2 (ACE2) receptor to enter host cells, and neutralizing antibodies are effective at blocking this interaction to prevent infection. Widespread application of this important marker of protective immunity is limited by logistical and technical challenges associated with live virus methods and venous blood collection. To address this gap, we validated an immunoassay-based method for quantifying neutralization of the spike-ACE2 interaction in a single drop of capillary whole blood, collected on filter paper as a dried blood spot (DBS) sample. Samples are eluted overnight and incubated in the presence of spike antigen and ACE2 in a 96-well solid phase plate. Competitive immunoassay with electrochemiluminescent label is used to quantify neutralizing activity. The following measures of assay performance were evaluated: dilution series of confirmed positive and negative samples, agreement with results from matched DBS-serum samples, analysis of results from DBS samples with known COVID-19 status, and precision (intra-assay percent coefficient of variation; %CV) and reliability (inter-assay; %CV). Dilution series produced the expected pattern of dose–response. Agreement between results from serum and DBS samples was high, with concordance correlation = 0.991. Analysis of three control samples across the measurement range indicated acceptable levels of precision and reliability. Median % surrogate neutralization was 46.9 for PCR confirmed convalescent COVID-19 samples and 0.1 for negative samples. Large-scale testing is important for quantifying neutralizing antibodies that can provide protection against COVID-19 in order to estimate the level of immunity in the general population. DBS provides a minimally-invasive, low cost alternative to venous blood collection, and this scalable immunoassay-based method for quantifying inhibition of the spike-ACE2 interaction can be used as a surrogate for virus-based assays to expand testing across a wide range of settings and populations.

scholarly journals Mammalian cell invasion and intracellular trafficking by Trypanosoma cruzi infective forms

2005 ◽  
Vol 77 (1) ◽  
pp. 77-94 ◽  
Author(s):  
Renato A. Mortara ◽  
Walter K. Andreoli ◽  
Noemi N. Taniwaki ◽  
Adriana B. Fernandes ◽  
Claudio V. da Silva ◽  
...  
Keyword(s):  
Trypanosoma Cruzi ◽  
Host Cell ◽  
Mammalian Cells ◽  
Parasitophorous Vacuole ◽  
Host Cells ◽  
Mammalian Host ◽  
Target Cells ◽  
Sylvatic Cycle ◽  
Final Destination ◽  
Different Strains

Trypanosoma cruzi, the etiological agent of Chagas’ disease, occurs as different strains or isolates that may be grouped in two major phylogenetic lineages: T. cruzi I, associated with the sylvatic cycle and T. cruzi II, linked to the human disease. In the mammalian host the parasite has to invade cells and many studies implicated the flagellated trypomastigotes in this process. Several parasite surface components and some of host cell receptors with which they interact have been identified. Our work focused on how amastigotes, usually found growing in the cytoplasm, can invade mammalian cells with infectivities comparable to that of trypomastigotes. We found differences in cellular responses induced by amastigotes and trypomastigotes regarding cytoskeletal components and actin-rich projections. Extracellularly generated amastigotes of T. cruzi I strains may display greater infectivity than metacyclic trypomastigotes towards cultured cell lines as well as target cells that have modified expression of different classes of cellular components. Cultured host cells harboring the bacterium Coxiella burnetii allowed us to gain new insights into the trafficking properties of the different infective forms of T. cruzi, disclosing unexpected requirements for the parasite to transit between the parasitophorous vacuole to its final destination in the host cell cytoplasm.

scholarly journals MicroRNA-Regulated Rickettsial Invasion into Host Endothelium via Fibroblast Growth Factor 2 and Its Receptor FGFR1

Cells ◽  
2018 ◽  
Vol 7 (12) ◽  
pp. 240 ◽  
Author(s):  
Abha Sahni ◽  
Hema Narra ◽  
Jignesh Patel ◽  
Sanjeev Sahni
Keyword(s):  
Gene Expression ◽  
Endothelial Cells ◽  
Growth Factor ◽  
Fibroblast Growth Factor ◽  
Host Cells ◽  
Microvascular Endothelial Cells ◽  
Target Cells ◽  
Fibroblast Growth ◽  
Wide Range ◽  
Microvascular Endothelial

Microvascular endothelial cells (ECs) represent the primary target cells during human rickettsioses and respond to infection via the activation of immediate–early signaling cascades and the resultant induction of gene expression. As small noncoding RNAs dispersed throughout the genome, microRNAs (miRNAs) regulate gene expression post-transcriptionally to govern a wide range of biological processes. Based on our recent findings demonstrating the involvement of fibroblast growth factor receptor 1 (FGFR1) in facilitating rickettsial invasion into host cells and published reports suggesting miR-424 and miR-503 as regulators of FGF2/FGFR1, we measured the expression of miR-424 and miR-503 during R. conorii infection of human dermal microvascular endothelial cells (HMECs). Our results revealed a significant decrease in miR-424 and miR-503 expression in apparent correlation with increased expression of FGF2 and FGFR1. Considering the established phenomenon of endothelial heterogeneity and pulmonary and cerebral edema as the prominent pathogenic features of rickettsial infections, and significant pathogen burden in the lungs and brain in established mouse models of disease, we next quantified miR-424 and miR-503 expression in pulmonary and cerebral microvascular ECs. Again, R. conorii infection dramatically downregulated both miRNAs in these tissue-specific ECs as early as 30 min post-infection in correlation with higher FGF2/FGFR1 expression. Changes in the expression of both miRNAs and FGF2/FGFR1 were next confirmed in a mouse model of R. conorii infection. Furthermore, miR-424 overexpression via transfection of a mimic into host ECs reduced the expression of FGF2/FGFR1 and gave a corresponding decrease in R. conorii invasion, while an inhibitor of miR-424 had the expected opposite effect. Together, these findings implicate the rickettsial manipulation of host gene expression via regulatory miRNAs to ensure efficient cellular entry as the critical requirement to establish intracellular infection.

scholarly journals Molecular Dissection of the Campylobacter jejuni CadF and FlpA Virulence Proteins in Binding to Host Cell Fibronectin

2020 ◽  
Vol 8 (3) ◽  
pp. 389 ◽  
Author(s):  
Prabhat K. Talukdar ◽  
Nicholas M. Negretti ◽  
Kyrah L. Turner ◽  
Michael E. Konkel
Keyword(s):  
Host Cell ◽  
Campylobacter Jejuni ◽  
Mapk Signaling ◽  
Effector Proteins ◽  
Host Cells ◽  
Target Cells ◽  
Cell Binding ◽  
Virulence Proteins ◽  
Host Target ◽  
Cell Signaling Pathways

Campylobacter jejuni, a zoonotic pathogen that frequently colonizes poultry, possesses two Microbial Surface Components Recognizing Adhesive Matrix Molecule(s) (MSCRAMMs) termed CadF and FlpA that bind to the glycoprotein fibronectin (FN). Previous to this study, it was not known whether the CadF and FlpA proteins were functionally redundant or if both were required to potentiate host cell binding and signaling processes. We addressed these questions by generating a complete repertoire of cadF and flpA mutants and complemented isolates, and performing multiple phenotypic assays. Both CadF and FlpA were found to be necessary for the maximal binding of C. jejuni to FN and to host cells. In addition, both CadF and FlpA are required for the delivery of the C. jejuni Cia effector proteins into the cytosol of host target cells, which in turn activates the MAPK signaling pathway (Erk 1/2) that is required for the C. jejuni invasion of host cells. These data demonstrate the non-redundant and bi-functional nature of these two C. jejuni FN-binding proteins. Taken together, the C. jejuni CadF and FlpA adhesins facilitate the binding of C. jejuni to the host cells, permit delivery of effector proteins into the cytosol of a host target cell, and aid in the rewiring of host cell signaling pathways to alter host cell behavior.

scholarly journals Glycosylation of the Major Polar Tube Protein of Encephalitozoon hellem, a Microsporidian Parasite That Infects Humans

2004 ◽  
Vol 72 (11) ◽  
pp. 6341-6350 ◽  
Author(s):  
Yanji Xu ◽  
Peter M. Takvorian ◽  
Ann Cali ◽  
George Orr ◽  
Louis M. Weiss
Keyword(s):  
Host Cell ◽  
Host Cells ◽  
Polar Tube ◽  
Microsporidian Parasite ◽  
Obligate Intracellular ◽  
Species Analysis ◽  
Wide Range ◽  
Mannose Binding ◽  
Microsporidia Species ◽  
Increased Susceptibility

ABSTRACT The microsporidia are ubiquitous, obligate intracellular eukaryotic spore-forming parasites infecting a wide range of invertebrates and vertebrates, including humans. The defining structure of microsporidia is the polar tube, which forms a hollow tube through which the sporoplasm is transferred to the host cell. Research on the molecular and cellular biology of the polar tube has resulted in the identification of three polar tube proteins: PTP1, PTP2, and PTP3. The major polar tube protein, PTP1, accounts for at least 70% of the mass of the polar tube. In the present study, PTP1 was found to be posttranslationally modified. Concanavalin A (ConA) bound to PTP1 and to the polar tube of several different microsporidia species. Analysis of the glycosylation of Encephalitozoon hellem PTP1 suggested that it is modified by O-linked mannosylation, and ConA binds to these O-linked mannose residues. Mannose pretreatment of RK13 host cells decreased their infection by E. hellem, consistent with an interaction between the mannosylation of PTP1 and some unknown host cell mannose-binding molecule. A CHO cell line (Lec1) that is unable to synthesize complex-type N-linked oligosaccharides had an increased susceptibility to E. hellem infection compared to wild-type CHO cells. These data suggest that the O-mannosylation of PTP1 may have functional significance for the ability of microsporidia to invade their host cells.

scholarly journals RpoH Mediates the Expression of Some, but Not All, Genes Induced in Neisseria gonorrhoeae Adherent to Epithelial Cells

2006 ◽  
Vol 74 (5) ◽  
pp. 2767-2776 ◽  
Author(s):  
Ying Du ◽  
Cindy Grove Arvidson
Keyword(s):  
Epithelial Cells ◽  
Neisseria Gonorrhoeae ◽  
Host Cell ◽  
Infection Process ◽  
Host Cells ◽  
Cell Contact ◽  
Transmitted Infection ◽  
New Host ◽  
Sexually Transmitted ◽  
Cell Induction

ABSTRACT Neisseria gonorrhoeae (gonococcus [GC]), is highly adapted to the human host, the only known reservoir for gonococcal infection. However, since it is sexually transmitted, infection of a new host likely requires a regulatory response on the part of the gonococcus to respond to this significant change in environment. We previously showed that adherence of gonococci to epithelial cells results in changes of gene expression in the bacteria that presumably prepare them for subsequent steps in the infection process. Expression of the heat shock sigma factor gene, rpoH, was shown to be important for the invasion step, as gonococci depleted for rpoH were reduced in their ability to invade epithelial cells. Here, we show that of the genes induced in adherent gonococci, two are part of the gonococcal RpoH regulon. When RpoH is depleted, expression of these genes is no longer induced by host cell contact, indicating that RpoH is mediating the host cell induction response of these genes. One RpoH-dependent gene, NGO0376, is shown to be important for invasion of epithelial cells, consistent with earlier observations that RpoH is necessary for this step of infection. Two genes, NGO1684 and NGO0340, while greatly induced by host cell contact, were found to be RpoH independent, indicating that more than one regulator is involved in the response to host cell contact. Furthermore, NGO0340, but not NGO1684, was shown to be important for both adherence and invasion of epithelial cells, suggesting a complex regulatory network in the response of gonococci to contact with host cells.

scholarly journals Visualization of the type III secretion mediated Salmonella–host cell interface using cryo-electron tomography

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Donghyun Park ◽  
Maria Lara-Tejero ◽  
M Neal Waxham ◽  
Wenwei Li ◽  
Bo Hu ◽  
...  
Keyword(s):  
Cell Membrane ◽  
Host Cell ◽  
Protein Secretion ◽  
Electron Tomography ◽  
Host Cells ◽  
Target Cells ◽  
Secretion Systems ◽  
Type Iii ◽  
Cryo Electron Tomography ◽  
Cell Interface

Many important gram-negative bacterial pathogens use highly sophisticated type III protein secretion systems (T3SSs) to establish complex host-pathogen interactions. Bacterial-host cell contact triggers the activation of the T3SS and the subsequent insertion of a translocon pore into the target cell membrane, which serves as a conduit for the passage of effector proteins. Therefore the initial interaction between T3SS-bearing bacteria and host cells is the critical step in the deployment of the protein secretion machine, yet this process remains poorly understood. Here, we use high-throughput cryo-electron tomography (cryo-ET) to visualize the T3SS-mediated Salmonella-host cell interface. Our analysis reveals the intact translocon at an unprecedented level of resolution, its deployment in the host cell membrane, and the establishment of an intimate association between the bacteria and the target cells, which is essential for effector translocation. Our studies provide critical data supporting the long postulated direct injection model for effector translocation.

scholarly journals Visualization of the type III secretion mediated Salmonella -host cell interface using cryo-electron tomography

2018 ◽  
Author(s):  
Jun Liu ◽  
Donghyun Park ◽  
Maria Lara-Tejero ◽  
Jorge E Galan ◽  
Wenwei Li ◽  
...  
Keyword(s):  
Cell Membrane ◽  
Host Cell ◽  
Type Iii Secretion ◽  
Electron Tomography ◽  
Host Cells ◽  
Target Cells ◽  
Secretion Systems ◽  
Type Iii ◽  
Cryo Electron Tomography ◽  
Cell Interface

Many important gram-negative bacterial pathogens use highly sophisticated type III secretion systems (T3SSs) to establish complex host-pathogen interactions. Bacterial-host cell contact triggers the activation of the T3SS and the subsequent insertion of a translocon pore into the target cell membrane, which serves as a conduit for the passage of effector proteins. Therefore the initial interaction between T3SS-bearing bacteria and host cells is the critical step in the deployment of the protein secretion machine, yet this process remains poorly understood. Here, we use high-throughput cryo-electron tomography (cryo-ET) to visualize the T3SS-mediated Salmonella -host cell interface. Our analysis reveals the intact translocon at an unprecedented level of resolution, its deployment in the host cell membrane, and the establishment of an intimate association between the bacteria and the target cells, which is essential for effector translocation. Our studies provide critical data supporting the long postulated direct injection model for effector translocation.

scholarly journals EPEC Recruits a Cdc42-Specific GEF, Frabin, To Facilitate PAK Activation and Host Cell Colonization

mBio ◽  
2020 ◽  
Vol 11 (6) ◽  
Author(s):  
Vikash Singh ◽  
Peter J. Hume ◽  
Anthony Davidson ◽  
Vassilis Koronakis
Keyword(s):  
Escherichia Coli ◽  
Host Cell ◽  
Small Gtpases ◽  
Bacterial Attachment ◽  
Host Protein ◽  
Host Cells ◽  
Target Cells ◽  
Content Type ◽  
Activated State ◽  
Pedestal Formation

ABSTRACT Enteropathogenic Escherichia coli (EPEC) is an extracellular pathogen that tightly adheres to host cells by forming “actin pedestals” beneath the bacteria, a critical step in pathogenesis. EPEC injects effector proteins that manipulate host cell signaling cascades to trigger pedestal assembly. We have recently shown that one such effector, EspG, hijacks p21-activated kinase (PAK) and sustains its activated state to drive the cytoskeletal changes necessary for attachment of the pathogen to target cells. This EspG subversion of PAK required active Rho family small GTPases in the host cell. Here we show that EPEC itself promotes the activation of Rho GTPases by recruiting Frabin, a host guanine nucleotide exchange factor (GEF) for the Rho GTPase Cdc42. Cells devoid of Frabin showed significantly lower EPEC-induced PAK activation, pedestal formation, and bacterial attachment. Frabin recruitment to sites of EPEC attachment was driven by EspG and required localized enrichment of phosphatidylinositol 4,5-bisphosphate (PIP2) and host Arf6. Our findings identify Frabin as a key target for EPEC to ensure the activation status of cellular GTPases required for actin pedestal formation. IMPORTANCE Enteropathogenic Escherichia coli (EPEC) is a leading cause of diarrhea in children, especially in the developing world. EPEC initiates infection by attaching to cells in the host intestine, triggering the formation of actin-rich “pedestal” structures directly beneath the adherent pathogen. These bacteria inject their own receptor into host cells, which upon binding to a protein on the pathogen surface triggers pedestal formation. Multiple other proteins are also delivered into the cells of the host intestine, which work together to hijack host signaling pathways to drive pedestal production. Here we show how EPEC hijacks a host protein, Frabin, which creates the conditions in the cell necessary for the pathogen to manipulate a specific pathway that promotes pedestal formation. This provides new insights into this essential early stage in disease caused by EPEC.

scholarly journals Phospholipid Composition of PurifiedChlamydia trachomatis Mimics That of the Eucaryotic Host Cell

1998 ◽  
Vol 66 (8) ◽  
pp. 3727-3735 ◽  
Author(s):  
Grant M. Hatch ◽  
Grant McClarty
Keyword(s):  
Host Cell ◽  
Phospholipid Composition ◽  
Brefeldin A ◽  
Host Cells ◽  
Cho Cell ◽  
Experimental Conditions ◽  
Obligate Intracellular ◽  
Wide Range ◽  
Host Cell Surface ◽  
Cellular Phospholipid

ABSTRACT Chlamydia trachomatis is an obligate intracellular eubacterial parasite capable of infecting a wide range of eucaryotic host cells. Purified chlamydiae contain several lipids typically found in eucaryotes, and it has been established that eucaryotic lipids are transported from the host cell to the parasite. In this report, we examine the phospholipid composition of C. trachomatispurified from host cells grown under a variety of conditions in which the cellular phospholipid composition was altered. A mutant CHO cell line, with a thermolabile CDP-choline synthetase, was used to show that decreased host cell phosphatidylcholine levels had no significant effect on C. trachomatis growth. However, less phosphatidylcholine was transported to the parasite and purified elementary bodies contained decreased levels of phosphatidylcholine. Brefeldin A, fumonisin B1, and exogenous sphingomyelinase were used to alter levels of host cell sphingomyelin. None of the agents had a significant effect on C. trachomatisreplication. Treatment with fumonisin B1 and exogenous sphingomyelinase resulted in decreased levels of host cell sphingomyelin. This had no effect on glycerophospholipid trafficking to chlamydiae; however, sphingomyelin trafficking was reduced and elementary bodies purified from treated cells had reduced sphingomyelin content. Exposure to brefeldin A, which had no adverse effect on chlamydia growth, resulted in an increase in cellular levels of sphingomyelin and a concomitant increase in the amount of sphingomyelin in purified chlamydiae. Under the experimental conditions used, brefeldin A treatment had only a small effect on sphingomyelin trafficking to the host cell surface or to C. trachomatis. Thus, the final phospholipid composition of purified C. trachomatis mimics that of the host cell in which it is grown.

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