Biology subjects

Pandey, S.

Publications and source records attributed to Pandey, S..

At least 73 records · Page 4Linked to original sources

bioRxiv2023

Structural analyses of 'substrate-pH of activity' pairing observed in Polysaccharide lyases

Anionic polysaccharides found in nature are functionally and structurally diverse, and so are the polysaccharide lyases (PLs) which catalyse their degradation. Atomic superposition of various PL folds according to their cleavable substrate structure confirm the occurrence of structural convergence at PL active sites. This suggests that various PL folds have emerged to cleave a particular class of anionic polysaccharide during the course of evolution. While structural and mechanistic similarity of PLs active site have been highlighted in earlier studies, a detailed understanding regarding functional properties of this catalytic convergence remains an open question, especially the role of extrinsic factors such as pH in the context of substrate binding and catalysis. Our earlier structural and functional work on pH directed multi-substrate specificity of Smlt1473 inspired us to regroup PLs according to substrate type to analyse the pH dependence of their catalytic activity. Interestingly, we find that particular groups of substrates are cleaved in a particular pH range (acidic/neutral/basic) irrespective of PLs fold, boosting the idea of functional convergence as well. Based on this observation, we set out to define structurally and computationally the key constituents of an active site among PL families. This study delineates the structural determinants of conserved substrate-pH activity pairing within and between PL families.

biochemistry↗

bioRxiv2023

Organism-Wide Analysis of Sepsis Reveals Mechanisms of Systemic Inflammation

Sepsis is a systemic response to infection with life-threatening consequences. Our understanding of the impact of sepsis across organs of the body is rudimentary. Here, using mouse models of sepsis, we generate a dynamic, organism-wide map of the pathogenesis of the disease, revealing the spatiotemporal patterns of the effects of sepsis across tissues. These data revealed two interorgan mechanisms key in sepsis. First, we discover a simplifying principle in the systemic behavior of the cytokine network during sepsis, whereby a hierarchical cytokine circuit arising from the pairwise effects of TNF plus IL-18, IFN-{gamma}, or IL-1{beta} explains half of all the cellular effects of sepsis on 195 cell types across 9 organs. Second, we find that the secreted phospholipase PLA2G5 mediates hemolysis in blood, contributing to organ failure during sepsis. These results provide fundamental insights to help build a unifying mechanistic framework for the pathophysiological effects of sepsis on the body.

immunology↗

bioRxiv2022

Heterogeneity in the M. tuberculosis β-lactamase inhibition by Sulbactam

For decades, researchers have been determined to elucidate essential enzymatic functions on the atomic lengths scale by tracing atomic positions in real time. Our work builds on new possibilities unleashed by mix-and-inject serial crystallography (MISC)1-5 at X-ray free electron laser facilities. In this approach, enzymatic reactions are triggered by mixing substrate or ligand solutions with enzyme microcrystals6. Here, we report in atomic detail and with millisecond time-resolution how the Mycobacterium tuberculosis enzyme BlaC is inhibited by sulbactam (SUB). Our results reveal ligand binding heterogeneity, ligand gating7-9, cooperativity, induced fit10,11 and conformational selection11-13 all from the same set of MISC data, detailing how SUB approaches the catalytic clefts and binds to the enzyme non-covalently before reacting to a trans-enamine. This was made possible in part by the application of the singular value decomposition14 to the MISC data using a newly developed program that remains functional even if unit cell parameters change during the reaction.

molecular biology↗

bioRxiv2022

NRPreTo: A Machine Learning Based Nuclear Receptor and Subfamily Prediction Tool

The Nuclear Receptor (NR) superfamily includes phylogenetically related ligand-activated proteins, which play a key role in various cellular activities. NR proteins are subdivided into seven subfamilies based on their function, mechanism, and nature of the interacting ligand. Developing robust tools to identify NR could give insights into their functional relationships and involvement in disease pathways. Existing NR prediction tools only use a few types of sequence-based features and are tested on relatively similar independent datasets; thus, they may suffer from overfitting when extended to new genera of sequences. To address this problem, we developed Nuclear Receptor Prediction Tool (NRPreTo); a two-level NR prediction tool with a unique training approach where in addition to the sequence-based features used by existing NR prediction tools, six additional feature groups depicting various physiochemical, structural and evolutionary features of proteins were utilized. The first level of NRPreTo allows for the successful prediction of a query protein as NR or non-NR, and further subclassifies the protein into one of the seven NR subfamilies in the second level. We developed Random Forest classifiers to test on benchmark datasets, as well as the entire human protein datasets from RefSeq and Human Protein Reference Database (HPRD). We observed that using additional feature groups improved performance. We also observed that NRPreTo achieved high performance on the external datasets and predicted 59 novel NRs in the human proteome. The source code of NRPreTo is publicly available at https://github.com/bozdaglab/NRPreTo.

systems biology↗

bioRxiv2022

A conserved population of MHC II-restricted, innate-like, commensal-reactive T cells in the gut of humans and mice

Interactions with commensal microbes shape host immunity on multiple levels and are recognized to play a pivotal role in human health and disease. In this study, we show that MHC-II restricted, commensal-reactive T cells in the colon of both humans and mice acquire transcriptional and functional characteristics typically associated with innate-like T cells, including the expression of the key transcription factor PLZF and the ability to respond to cytokines including IL-12, IL-18 and IL-23 in a TCR-independent manner. These MHC-II restricted, innate-like, commensal-reactive T cells (TMIC) are endowed with a polyfunctional effector potential spanning classic Th1- and Th17-cytokines, cytotoxic molecules as well as regulators of epithelial homeostasis and represent an abundant and conserved cell population in the human and murine colon. T cells with the TMIC phenotype were increased in ulcerative colitis patients and their presence aggravated pathology in DSS-treated mice, pointing towards a pathogenic role in colitis. Our findings add TMIC cells to the expanding spectrum of innate-like immune cells positioned at the frontline of intestinal immune surveillance, capable of acting as sentinels of microbes and the local cytokine milieu.

immunology↗

bioRxiv2022

Niacinamide enhances cathelicidin mediated SARS-CoV-2 membrane disruption

The continual emergence of new SARS-CoV-2 variants threatens the effectiveness of worldwide vaccination programs and highlights the need for complementary strategies for a sustainable containment plan. A promising approach is to mobilize the bodys own antimicrobial peptides (AMPs), to combat SARS-CoV-2 infection and propagation. We have found that human cathelicidin (LL37), an AMP found at epithelial barriers as well as in various bodily fluids, has the capacity to neutralise multiple strains of SARS-CoV-2. Biophysical and computational studies indicate that LL37s mechanism of action is through the disruption of the viral membrane. This antiviral activity of LL37 is enhanced by the hydrotropic action of niacinamide, which may increase the bioavailability of the AMP. Interestingly, we observed inverse correlation between LL37 levels and disease severity of COVID-19 positive patients, suggesting enhancement of AMP response would be an effective therapeutic avenue to mitigate disease severity and overcome vaccine escape.

pathology↗

bioRxiv2022

CRISPR/Cas9 and FLP-FRT mediated multi-modular engineering of the cis-regulatory landscape of the bithorax complex of Drosophila melanogaster

The Homeotic genes or Hox define the anterior-posterior (AP) body axis formation in bilaterians and are often present on the chromosome in an order which is collinear to their function across the AP axis. The expression pattern of Hox genes is attributed to the cis-regulatory modules (CRMs) that regulate the genes in a segment-specific manner. In the bithorax complex (BX-C), one of the two Hox complexes in Drosophila melanogaster, even the CRMs consisting of enhancers, initiators, insulators, and Polycomb/trithorax response elements are organized in order that is collinear to their function in the thoracic and abdominal region. Much of these findings are based on the analysis of hundreds of mutations in the BX-C. However, targeted genomic rearrangements comprising of duplications, inversions, etc., that can reveal the basis of collinearity and the number of regulatory modules with respect to body segments have not been reported. In the present study, we generated a series of transgenic lines with the insertion of FRT near the regulatory domain boundaries, to shuffle the CRMs associated with the posterior Hox, Abd-B, of the BX-C. Using these FRT lines, we created several alterations such as deletion, duplication, or inversion of multiple CRMs to comprehend their peculiar genomic arrangement and numbers in the BX-C.

developmental biology↗

bioRxiv2022

Molecular insights into intrinsic transducer-coupling bias in the CXCR4-CXCR7 system

Chemokine receptors constitute an important subfamily of G protein-coupled receptors (GPCRs), and they are critically involved in a broad range of immune response mechanisms. Ligand promiscuity among these receptors makes them an interesting target to explore novel aspects of biased agonism. Here, we comprehensively characterize two chemokine receptors namely, CXCR4 and CXCR7, which share a common chemokine agonist (CXCL12), in terms of their G-protein coupling, {beta}-arrestin ({beta}arr) recruitment, contribution of GRKs, and ERK1/2 MAP kinase activation. We observe that CXCR7 lacks G-protein coupling while maintaining robust {beta}arr recruitment with a major contribution of GRK5/6. On the other hand, CXCR4 displays robust G-protein activation as expected, however, it exhibits significantly reduced {beta}arr-coupling compared to CXCR7 in response to their shared natural agonist, CXCL12. These two receptors induce distinct {beta}arr conformations even when activated by the same agonist, and CXCR7, unlike CXCR4, fails to activate ERK1/2 MAP kinase. We further determine the crystal structure of {beta}arr2 in complex with a carboxyl-terminal phosphopeptide derived from CXCR7, which reveals a smaller interdomain rotation than observed previously for activated {beta}arrs. Importantly, structure-guided cellular experiments reveal a key contribution of a single phosphorylation site in CXCR7 on {beta}arr recruitment and endosomal trafficking. Taken together, our study provides molecular insights into intrinsic bias encoded in the CXCR4-CXCR7 system, and it has broad implications for therapeutically important framework of biased agonism.

biochemistry↗

bioRxiv2022

NtcA, LexA and heptamer repeats involved in the multifaceted regulation of DNA repair genes recF, recO and recR in the cyanobacterium Nostoc PCC7120

Regulation of DNA repair genes in cyanobacteria is an unexplored field despite some of them exhibit high radio-resistance. With the RecF pathway speculated to be the major double strand break repair pathway in Nostoc sp. strain PCC7120, the regulation of recF, recO and recR genes was investigated. Bioinformatic approach-based identification of promoter and regulatory elements was validated using qRT-PCR analysis, reporter gene and DNA binding assays. Different deletion constructs of the upstream regulatory regions of these genes were analysed in host Nostoc as well as heterologous system Escherichia coli. Studies revealed: (1) Positive regulation of all three genes by NtcA, (2) Negative regulation by LexA, (3) Involvement of contiguous heptamer repeats with/without its yet to be identified interacting partner in regulating (i) binding of NtcA and LexA to recO promoter and its translation, (ii) transcription or translation of recF, (4) Translational regulation of recF and recO through non-canonical and distant S.D. sequence and of recR through a rare initiation codon. Presence of NtcA either precludes binding of LexA to AnLexA-Box or negates its repressive action resulting in higher expression of these genes under nitrogen-fixing conditions in Nostoc. Thus, in Nostoc, expression of recF, recO and recR genes is intricately regulated through multiple regulatory elements/proteins. Contiguous heptamer repeats present across the Nostoc genome in the vicinity of start codon or promoter is likely to have a global regulatory role. This is the first report on the involvement of NtcA and heptamer repeats in regulation of DNA repair genes in any organism.

molecular biology↗

bioRxiv2022

Activation of targetable inflammatory immune signaling is seen in Myelodysplastic Syndromes with SF3B1 mutations

BackgroundMutations in the SF3B1 splicing factor are commonly seen in Myelodysplastic syndromes (MDS) and Acute Myeloid Leukemia (AML), yet the specific oncogenic pathways activated by missplicing have not been fully elucidated. Inflammatory immune pathways have been shown to play roles in pathogenesis of MDS, though the exact mechanisms of their activation in splicing mutant cases are not well understood. MethodsRNA-seq data from SF3B1 mutant samples was analyzed and functional roles of IRAK4 isoforms were determined. Efficacy of IRAK4 inhibition was evaluated in pre-clinical models of MDS/AML ResultsRNA-seq splicing analysis of innate immune mediators in SF3B1 mutant MDS samples revealed retention of full-length exon 6 of interleukin-1 receptor-associated kinase 4 (IRAK4), a critical downstream mediator that links the Myddosome to inflammatory NF-kB activation. Exon 6 retention leads to a longer isoform, encoding a protein (IRAK4-Long) that contains the entire death domain and kinase domain, leading to maximal activation of NF-kB. Cells with wild-type SF3B1 contain smaller IRAK4 isoforms that are targeted for proteosomal degradation. Expression of IRAK4-Long in SF3B1 mutant cells induces TRAF6 activation leading to K63-linked ubiquitination of CDK2, associated with a block in hematopoietic differentiation. Inhibition of IRAK4 with CA-4948, leads to reduction in NF-kB activation, inflammatory cytokine production, enhanced myeloid differentiation in vitro and reduced leukemic growth in xenograft models. ConclusionsSF3B1 mutation leads to expression of a therapeutically targetable, longer, oncogenic IRAK4 isoform in AML/MDS models.

cancer biology↗

bioRxiv2022

Highly Thermotolerant SARS-CoV-2 Vaccine Elicits Neutralising Antibodies Against Delta and Omicron in Mice

As existing vaccines fail to completely prevent COVID-19 infections or community transmission, there is an unmet need for vaccines that can better combat SARS-CoV-2 variants of concern (VOC). We have previously developed highly thermo-tolerant monomeric and trimeric receptor binding domain derivatives that can withstand 100{degrees}C for 90 minutes and 37{degrees}C for four weeks, and help eliminate cold chain requirements. We show that mice immunised with these vaccine formulations elicit high titres of antibodies that neutralise SARS-CoV-2 variants VIC31 (with Spike: D614G mutation), Delta and Omicron (BA.1.1) VOC. Compared to VIC31, there was an average 14.4-fold reduction in neutralisation against BA.1.1 for the three monomeric antigen-adjuvant combinations, and 16.5-fold reduction for the three trimeric antigen-adjuvant combinations; the corresponding values against Delta were 2.5 and 3.0. Our findings suggest that monomeric formulations are suitable for the upcoming Phase I human clinical trials, and that there is potential for increasing efficacy with vaccine matching to improve responses against emerging variants. These findings are consistent with in silico modelling and AlphaFold predictions which show that while oligomeric presentation can be generally beneficial, it can make important epitopes inaccessible, and also carries the risk of eliciting unwanted antibodies against the oligomerisation domain.

immunology↗

bioRxiv2022

Allosteric modulation of GPCR-induced β-arrestin trafficking and signaling by a synthetic intrabody

Agonist-induced phosphorylation of G protein-coupled receptors (GPCRs) is a primary determinant of {beta}-arrestin ({beta}arr) recruitment and trafficking. For several GPCRs, such as the vasopressin type II receptor (V2R), which exhibit high affinity for {beta}arrs, agonist-stimulation first drives the translocation of {beta}arrs to the plasma membrane, followed by endosomal trafficking. We previously found that mutation of a single phosphorylation site in V2R (i.e., V2RT360A) results in near-complete loss of {beta}arr translocation to endosomes although {beta}arrs are robustly recruited to the plasma membrane. Here, we show that a synthetic intrabody referred to as intrabody30 (Ib30), which selectively recognizes an active-like {beta}arr1 conformation, rescues endosomal translocation of {beta}arr1 for V2RT360A. In addition, Ib30 also rescues agonist-induced ERK1/2 MAP kinase activation for V2RT360A to levels similar to that of the wild-type V2R. Molecular dynamics simulations reveal that Ib30 binding promotes active-like conformation in {beta}arr1 with respect to the inter-domain rotation. Interestingly, we also observe that Ib30 enhances the interaction of {beta}arr1 with {beta}2-adaptin, which provides a mechanistic basis for the ability of Ib30 to promote endosomal trafficking of {beta}arr1. Taken together, our data provide a novel mechanism to positively modulate the receptor-transducer-effector axis for GPCRs using intrabodies, which can potentially be integrated in the current paradigm of GPCR-targeted drug discovery. SignificanceThe interaction of G protein-coupled receptors (GPCRs) with {beta}-arrestins ({beta}arrs) is a critical step in their regulatory and signaling paradigms. While intrabodies that bind to GPCRs, G proteins and {beta}arrs have been utilized as biosensors and regulators of functional outcomes, allosteric targeting of receptor-transducer complexes to encode gain of function has not been documented so far. Here, we discover that a conformation-specific synthetic intrabody recognizing GPCR-bound {beta}arr1 can allosterically enhance endosomal trafficking of {beta}arr1 and agonist-induced ERK1/2 MAP kinase activation. This intrabody promotes an active-like {beta}arr1 conformation and enhances the interaction of {beta}2-adaptin with {beta}arr1. Our findings establish a conceptual framework to allosterically modulate protein-protein interactions in GPCR signaling cascade to modulate their trafficking and signaling responses.

biochemistry↗

bioRxiv2021

Citrus Huanglongbing is an immune-mediated disease that can be treated by mitigating reactive oxygen species triggered cell death of the phloem tissues caused by Candidatus Liberibacter asiaticus

The immune system is critical for keeping animals and plants healthy from pathogens. However, immune-mediated diseases are also common for human. Immune-mediated diseases have not been reported for plants. Here, we present evidence that citrus Huanglongbing (HLB), caused by phloem-colonizing Candidatus Liberibacter asiaticus (CLas), is an immune-mediated disease. CLas infection of Citrus sinensis stimulated systemic and chronic immune response in the phloem tissues including reactive oxygen species (ROS) production as indicated by H2O2, callose deposition, and induction of immune related genes. Systemic cell death of companion and sieve element cells, but not surrounding parenchyma cells, was observed following ROS production triggered by CLas. ROS production triggered by CLas localized in phloem tissues. The H2O2 concentration in exudates extracted from phloem enriched bark tissue of CLas infected plants reached a threshold of killing citrus protoplast cells, which was suppressed by uric acid (a ROS scavenger) and gibberellin. Foliar spray of HLB positive citrus with antioxidants (uric acid and rutin) and gibberellin significantly reduced both H2O2 concentrations and cell death in phloem tissues induced by CLas and reduced HLB symptoms. RNA-seq analyses of CLas infected and health C. sinensis support that CLas causes oxidative stress. In sum, HLB is an immune-mediated disease and both mitigating ROS via antioxidants and promoting plant growth can reduce cell death of the phloem tissues caused by CLas, thus controlling HLB.

plant biology↗

bioRxiv2021

A novel binary k-mer approach for classification of coding and non-coding RNAs across diverse species

Classification among coding (CDS) and non-coding RNA (ncRNA) sequences is a challenge and several machine learning models have been developed for the same. Since the frequency of curated coding sequences is many-folds as compared to that of the ncRNAs, we devised a novel approach to work with the complete datasets from fifteen diverse species. In our proposed novel binary approach, we replaced all the As and Ts with 0s and Gs and Cs with 1s to obtain a binary form of coding and ncRNAs. The k-mer analysis of these binary sequences revealed that the frequency of binary patterns among the coding and ncRNAs can be used as features to distinguish among them. Using insights from these distinguishing frequencies, we used k-nearest neighbour classifier to classify among them. Our strategy is not only time-efficient but leads to significantly increased performance metrics including Matthews correlation coefficient (MCC) for some species like P. paniscus, M. mulatta, M. lucifugus, G. gallus, C. japonica, C. abingdonii, A. carolinensis, D. melanogaster and C. elegans when compared with the conventional ATGC approach. Additionally, we also show that the values of MCC obtained for diverse species tested on the model based on H. sapiens correlated with the geological evolutionary timeline thereby further strengthening our approach. Therefore, we propose that CDS and ncRNAs can be efficiently classified using "2-character" frequency as compared to "4-character" frequency of ATGC approach. Thus, our highly efficient binary approach can replace the more complex ATGC approach successfully.

genomics↗

bioRxiv2021

Vitamin C inhibits SARS coronavirus-2 main protease essential for viral replication

There is an urgent need for anti-viral agents that treat and/or prevent Covid-19 caused by SARS-Coronavirus (CoV-2) infections. The replication of the SARS CoV-2 is dependent on the activity of two cysteine proteases, a papain-like protease, PL-pro, and the 3C-like protease known as main protease Mpro or 3CLpro. The shortest and the safest path to clinical use is the repurposing of drugs with binding affinity to PLpro or 3CLpro that have an established safety profile in humans. Several studies have reported crystal structures of SARS-CoV-2 main protease in complex with FDA approved drugs such as those used in treatment of hepatitis C. Here, we report the crystal structure of 3CLpro in complex Vitamin C (L-ascorbate) bound to the proteins active site at 2.5 [A]ngstrom resolution. The crystal structure of the Vitamin C 3CLpro complex may aid future studies on the effect of Vitamin C not only on the coronavirus main protease but on related proteases of other infectious viruses.

biophysics↗

bioRxiv2021

Design of bacterially expressed influenza stem immunogens displayed on Msdps2 protein nanoparticles

Current influenza vaccines need to be updated annually due to mutations in the globular head of the viral surface protein, hemagglutinin (HA). To address this, vaccine candidates have been designed based on the relatively conserved HA stem domain and have shown protective efficacy in animal models. Oligomerization of the antigens either by fusion to oligomerization motifs or display on self-assembling nanoparticle scaffolds, can induce more potent immune responses compared to the corresponding monomeric antigen due to multivalent engagement of B-cells. Since nanoparticle display can increase manufacturing complexity, and often involves one or more mammalian cell expressed components, it is important to characterize and compare various display and oligomerization scaffolds. Using a structure guided approach, we successfully displayed multiple copies of a previously designed soluble, trimeric influenza stem domain immunogen, pH1HA10, on the ferritin like protein, MsDps2 (12 copies), Ferritin (24 copies) and Encapsulin (180 copies). All proteins were expressed in Escherichia coli. The nanoparticle fusion immunogens were found to be well folded and bound to the influenza stem directed broadly neutralizing antibodies with high affinity. An 8.5 [A] Cryo-EM map of Msdps2-pH1HA10 confirmed the successful design of the nanoparticle fusion immunogen. Mice immunization studies with the soluble trimeric stem and nanoparticle fusion constructs revealed that all of them were immunogenic, and protected mice against homologous (A/Belgium/145-MA/2009) and heterologous (A/Puerto Rico/8/1934) challenge with 10MLD50 mouse adapted virus. Although nanoparticle display conferred a small but statistically significant improvement in protection relative to the soluble trimer in a homologous challenge, heterologous protection was similar in both nanoparticle-stem immunized and trimeric stem immunized groups. Such rapidly producible, bacterially expressed antigens and nanoparticle scaffolds are useful modalities to tackle future influenza pandemics.

immunology↗

bioRxiv2021

Invariant Differential Expression Analysis Reveals Mechanism of Cancer Resistance to Cell Cycle Inhibitors

Retinoblastoma (RB) is a good model to study drug resistance to cell-cycle inhibitors because it is driven by mutations in the core components of cell-cycle, i.e, Rb gene. However, there is limited gene expression dataset in RB which has major reproducibility issues. We have developed invariant differential expression analysis (iDEA) that improves the state of the art in differential expression analysis (DEA). iDEA uses strong Boolean implication relationships in a large diverse human dataset GSE119087 (n = 25,955) to filter the noisy differentially expressed genes (DEGs). iDEA was applied to RB datasets and a gene signature was computed that led to prediction and mechanism of drug sensitivity. The prediction was confirmed using drugs-sensitive/resistant RB cell-lines and mouse xenograft models using CDC25 inhibitor NSC663284. iDEA improved reproducibility of differential expression across diverse retina/RB cohorts and RB cell-lines with different drug sensitivity (Y79/Weri vs NCC). Pathway analysis revealed WNT/{beta}-catenin involved in distinguishing drug sensitivity to CDC25 inhibitor NSC663284. NSC663284 inhibited tumour cell proliferation in mouse xenograft model containing Y79 cells indicating novel therapeutic option in RB. Invariant differentially expressed genes (iDEGs) are robustly associated with outcome in diverse cancer datasets and supports for a fundamental mechanism of drug resistance.

systems biology↗

bioRxiv2021

Intrinsic bias at non-canonical, β-arrestin-coupled seven transmembrane receptors

G protein-coupled receptors (GPCRs) are typically characterized by their seven transmembrane (7TM) architecture, and interaction with two universal signal-transducers namely, the heterotrimeric G-proteins and {beta}-arrestins ({beta}arrs). Synthetic ligands and receptor mutants have been designed to elicit transducer-coupling preferences and distinct downstream signaling outcomes for many GPCRs. This raises the question if some naturally-occurring 7TMRs may selectively engage one of these two signal-transducers, even in response to their endogenous agonists. Although there are scattered hints in the literature that some 7TMRs lack G-protein coupling but interact with {beta}arrs, an in-depth understanding of their transducer-coupling preference, GRK-engagement, downstream signaling and structural mechanism remains elusive. Here, we use an array of cellular, biochemical and structural approaches to comprehensively characterize two non-canonical 7TMRs namely, the human decoy D6 receptor (D6R) and the human complement C5a receptor (C5aR2), in parallel with their canonical GPCR counterparts, CCR2 and C5aR1, respectively. We discover that D6R and C5aR2 couple exclusively to {beta}arrs, exhibit distinct GRK-preference, and activate non-canonical downstream signaling partners. We also observe that {beta}arrs, in complex with these receptors, adopt distinct conformations compared to their canonical GPCR counterparts despite being activated by a common natural agonist. Our study therefore establishes D6R and C5aR2 as bona-fide arrestin-coupled receptors (ACRs), and provides important insights into their regulation by GRKs and downstream signaling with direct implications for biased agonism.

biochemistry↗