Receptor-binding Features Research Articles

Variation and Molecular Basis for Enhancement of Receptor Binding of H9N2 Avian Influenza Viruses in China Isolates.

Currently, H9N2 avian influenza viruses (H9N2 AIVs) globally circulate in poultry and have acquired some adaptation to mammals. However, it is not clear what the molecular basis is for the variation in receptor-binding features of the H9N2 AIVs. The receptor-binding features of 92 H9N2 AIVs prevalent in China during 1994–2017 were characterized through solid-phase ELISA assay and reverse genetics. H9N2 AIVs that circulated in this period mostly belonged to clade h9.4.2. Two increasing incidents occurred in the ability of H9N2 AIVs to bind to avian-like receptors in 2002–2005 and 2011–2014. Two increasing incidents occurred in the strength of H9N2 AIVs to bind to human-like receptors in 2002–2005 and 2011–2017. We found that Q227M, D145G/N, S119R, and R246K mutations can significantly increase H9N2 AIVs to bind to both avian- and human-like receptors. A160D/N, Q156R, T205A, Q226L, V245I, V216L, D208E, T212I, R172Q, and S175N mutations can significantly enhance the strength of H9N2 AIVs to bind to human-like receptors. Our study also identified mutations T205A, D208E, V216L, Q226L, and V245I as the key sites leading to enhanced receptor binding of H9N2 AIVs during 2002–2005 and mutations S119R, D145G, Q156R, A160D, T212I, Q227M, and R246K as the key sites leading to enhanced receptor binding of H9N2 AIVs during 2011–2017. These findings further illustrate the receptor-binding characteristics of avian influenza viruses, which can be a potential threat to public health.

Insights into the antigenic advancement of influenza A(H3N2) viruses, 2011\u20132018

Influenza A(H3N2) viruses evade human immunity primarily by acquiring antigenic changes in the haemagglutinin (HA). HA receptor-binding features of contemporary A(H3N2) viruses hinder traditional antigenic characterization using haemagglutination inhibition and promote selection of HA mutants. Thus, alternative approaches are needed to reliably assess antigenic relatedness between circulating viruses and vaccines. We developed a high content imaging-based neutralization test (HINT) to reduce antigenic mischaracterization resulting from virus adaptation to cell culture. Ferret reference antisera were raised using clinical specimens containing viruses representing recent vaccine strains. Analysis of viruses circulating during 2011–2018 showed that gain of an N158-linked glycosylation in HA was a molecular determinant of antigenic distancing between A/Hong Kong/4801/2014-like (clade 3C.2a) and A/Texas/50/2012-like viruses (clade 3C.1), while multiple evolutionary HA F193S substitution were linked to antigenic distancing from A/Switzerland/97152963/2013-like (clade 3C.3a) and further antigenic distancing from A/Texas/50/2012-like viruses. Additionally, a few viruses carrying HA T135K and/or I192T showed reduced neutralization by A/Hong Kong/4801/2014-like antiserum. Notably, this technique elucidated the antigenic characteristics of clinical specimens, enabling direct characterization of viruses produced in vivo, and eliminating in vitro culture, which rapidly alters the genotype/phenotype. HINT is a valuable new antigenic analysis tool for vaccine strain selection.

Characteristics of influenza H13N8 subtype virus firstly isolated from Qinghai Lake Region, China

BackgroundSince the highly pathogenic H5N1 influenza caused thousands of deaths of wild bird in this area in 2005, Qinghai Lake in China has become a hot spot for study of the influence of avian influenza to migratory wild birds. However, the ecology and evolution of low pathogenic avian influenza virus in this region are limited. This project-based avian influenza surveillance in Qinghai lake region was initiated in year 2012.MethodSamples of wild bird feces and lake surface water were collected in Qinghai Lake in year 2012.Virus isolation was conducted on embryonated chicken eggs. The influenza A virus was determined by rRT-PCR. Virus sequences were acquired by deep sequencing. The phylogenetic correlation and molecular characteristics of the viruses were analyzed. The virus growth and infection features, receptor binding preference were studied, and pathogenicity in vitro as well as.ResultsTwo H13N8 subtype influenza viruses were isolated. The viruses are phylogenetically belong to Eurasian lineage. Most of the genes are associated with gull origin influenza virus except PB1 gene, which is most probably derived from Anseriformes virus. The evidence of interspecies reassortment was presented. The two viruses have limited growth capacity on MDCK and A549 cells while grow well in embryonated eggs. The dual receptor binding features of the two viruses was shown up. The low pathogenic features were determined by trypsin dependence plaque formation assay.ConclusionsThe two H13N8 subtype influenza viruses are highly associated with gull origin. The interspecies reassortment of H13 subtype virus among Anseriforme sand Charadriiformes wild birds emphasizes the importance of strengthening avian influenza surveillance in this region. This study is helpful to understand the ecology, evolution and transmission pattern of H13 subtype influenza virus globally.

Avian-to-Human Receptor-Binding Adaptation by Influenza A Virus Hemagglutinin H4

Low-pathogenicity avian influenza viruses (LPAIVs) have caused a global concern to public health since the first novel LPAIV H7N9 outbreak occurred. The receptor-binding properties of the viral hemagglutinin are one key factor for efficient transmission and infection in humans. Recent evidence shows that H4 subtype viruses have been widely circulating in domestic poultry and human asymptomatic infections might have occurred. Here, we evaluated the receptor-binding properties of two representative isolates, avian H4N6 (containing Q226 and G228) and swine H4N6 (containing L226 and S228), and found that the avian isolate preferentially binds to avian receptors, whereas the swine isolate preferentially binds to human receptors. The Q226L and G228S substitutions are pivotal for the receptor-binding switch, which resulted in similar human receptor-binding features to the pandemic H2 and H3, implying that H4 has the potential to cause human infections. This early-warning study calls for future extensive surveillance.

Crystal Structure of the TSH Receptor in Complex with a Thyroid-Stimulating Autoantibody

To analyze interactions between the thyroid-stimulating hormone receptor (TSHR) and a thyroid-stimulating human monoclonal autoantibody (M22) at the molecular level. A complex of part of the TSHR extracellular domain (amino acids 1-260; TSHR260) bound to M22 Fab was prepared and purified. Crystals suitable for X-ray diffraction analysis were obtained and the structure solved at 2.55 A resolution. TSHR260 comprises of a curved helical tube and M22 Fab clasps its concave surface at 90 degrees to the tube length axis. The interface buried in the complex is large (2,500 A(2)) and an extensive network of ionic, polar, and hydrophobic bonding is involved in the interaction. There is virtually no movement in the atoms of M22 residues on the binding interface compared to unbound M22 consistent with "lock and key" binding. Mutation of residues showing strong interactions in the structure influenced M22 activity, indicating that the binding detail observed in the complex reflects interactions of M22 with intact, functionally active TSHR. The receptor-binding arrangements of the autoantibody are very similar to those reported for follicle-stimulating hormone (FSH) binding to the FSH receptor (amino acids 1-268) and consequently to those of TSH itself. It is remarkable that the thyroid-stimulating autoantibody shows almost identical receptor-binding features to TSH although the structures and origins of these two ligands are very different. Furthermore, our structure of the TSHR and its complex with M22 provide foundations for developing new strategies to understand and control both glycoprotein hormone receptor activation and the autoimmune response to the TSHR.

The binding of arylguanidines at 5-HT 3 serotonin receptors: a structure–affinity investigation

The 5-HT 3 receptor binding affinities of nine pairs of aryl-substituted arylguanidines and arylbiguanides were examined and the results suggest the likelihood that both classes of agents utilize common receptor binding features. The effects of structural modification were also examined using CoMFA. 1-(3,4,5-Trichlorophenyl)guanidine (5-HT 3 K i=0.7 nM) was identified as a very high-affinity arylguanidine. The structures of the high-affinity arylguanidines are inconsistent with current 5-HT 3 pharmacophore models.

The DRIP complex and SRC-1/p160 coactivators share similar nuclear receptor binding determinants but constitute functionally distinct complexes.

Transcriptional activation requires both access to DNA assembled as chromatin and functional contact with components of the basal transcription machinery. Using the hormone-bound vitamin D(3) receptor (VDR) ligand binding domain (LBD) as an affinity matrix, we previously identified a novel multisubunit coactivator complex, DRIP (VDR-interacting proteins), required for transcriptional activation by nuclear receptors and several other transcription factors. In this report, we characterize the nuclear receptor binding features of DRIP205, a key subunit of the DRIP complex, that interacts directly with VDR and thyroid hormone receptor in response to ligand and anchors the other DRIP subunits to the nuclear receptor LBD. In common with other nuclear receptor coactivators, DRIP205 interaction occurs through one of two LXXLL motifs and requires the receptor's AF-2 subdomain. Although the second motif of DRIP205 is required only for VDR binding in vitro, both motifs are used in the context of an retinoid X receptor-VDR heterodimer on DNA and in transactivation in vivo. We demonstrate that both endogenous p160 coactivators and DRIP complexes bind to the VDR LBD from nuclear extracts through similar sequence requirements, but they do so as distinct complexes. Moreover, in contrast to the p160 family of coactivators, the DRIP complex is devoid of any histone acetyltransferase activity. The results demonstrate that different coactivator complexes with distinct functions bind to the same transactivation region of nuclear receptors, suggesting that they are both required for transcription activation by nuclear receptors.

The large diverse gene family var encodes proteins involved in cytoadherence and antigenic variation of plasmodium falciparum-infected erythrocytes

The human malaria parasite Plasmodium falciparum evades host immunity by varying the antigenic and adhesive character of infected erythrocytes. We describe a large and extremely diverse family of P. falciparum genes ( var) that encode 200–350 kDa proteins having the expected properties of antigenically variant adhesion molecules. Predicted amino acid sequences of var genes show a variable extracellular segment with domains having receptor-binding features, a transmembrane sequence, and a terminal segment that is a probable submembrane anchor. There are 50–150 var genes on multiple parasite chromosomes, and some are in clustered arrangements. var probes detect two classes of transcripts in steady-state RNA: 7–9 kb var transcripts, and an unusual family of 1.8 – 2.4 kb transcripts that may be involved in expression or re-arrangements of var genes.

The iodination sites of bovine thyrotropin.

Iodination of bovine thyrotropin (TSH) using a lactoperoxidase-catalyzed labeling method at pH 5.6 results in modification of both the alpha- and beta-subunits. In particular, 3 of the 5 tyrosine residues of the alpha-subunit and 9 of the 11 tyrosine residues in the beta-subunit are accessible to surface iodination. However, the reactivity of these tyrosine residues in bovine TSH toward iodination under these enzyme-catalyzed conditions follows the order alpha-Tyr-21 much greater than alpha-Tyr-92, -93, approximately equal to beta-Tyr-45, -54 greater than beta-Tyr-74 greater than beta-Tyr-18 approximately equal to beta-Tyr-112 greater than beta-Tyr-104 approximately equal to beta-Tyr-92 greater than beta-Tyr-7 greater than beta-Tyr-77. From reversed-phase high-performance liquid chromatography tryptic mapping, leucyl aminopeptidase M digestion, and microsequence analysis, it is clear that diiodination of the tyrosine residues is not favored for the beta-subunit with the exception of beta-Tyr-7, whereas diiodination was observed with alpha-Tyr-21 and alpha-Tyr-92/93. These data on iodination sites are evaluated in terms of the known receptor binding features of iodinated bovine TSH preparations as well as in terms of the surface accessibility of these specific residues as predicted from topographical algorithms based on an analysis of hydrophilic and hydrophobic regions of the subunits. The results provide an explanation for the anomalously low bound/total tracer ratio frequently observed in radioreceptor assay procedures for TSH and suggest a basis for further evaluation of the determinant loops associated with the hormone specificity of the beta-subunit.