GPCR Signaling: β-arrestins Kiss and Remember

Inverse Regulation of C-C Chemokine Receptor 3 Oligomerization by Downstream Proteins Indicates Biased Signal Transduction Pathways

Oligomerization is one of the important mechanisms for G protein-coupled receptors (GPCRs) to modulate their activity in signal transduction. However, details of how and why the oligomerization of GPCRs regulates their functions under physiological conditions remain largely unknown. Here, using single-molecule photobleaching technology, we show that chemokine ligand 5 (CCL5) and chemokine ligand 8 (CCL8) are similar to the previously reported chemokine ligand 11 (CCL11) and chemokine ligand 24 (CCL24), which can regulate the oligomerization of chemokine receptor 3 (CCR3). Our results further demonstrate that downstream proteins, β-arrestin 2 and Gi protein complex, on the CCR3 signal transduction pathway, can inversely regulate the oligomeric states of CCR3 induced by its binding ligands. This unexpected discovery suggests complex relationships between the oligomeric behaviors of CCR3 and the components of ligands-CCR3-downstream proteins, reflecting the potentially functional impact of the oligomerization on the multiple activation pathways of GPCR, such as biased activation.

Information Transmission in G Protein-Coupled Receptors

G protein-coupled receptors (GPCRs) are the largest class of receptors in the human genome and constitute about 30% of all drug targets. In this article, intended for a non-mathematical audience, both experimental observations and new theoretical results are compared in the context of information transmission across the cell membrane. The amount of information actually currently used or projected to be used in clinical settings is a small fraction of the information transmission capacity of the GPCR. This indicates that the number of yet undiscovered drug targets within GPCRs is much larger than what is currently known. Theoretical studies with some experimental validation indicate that localized heat deposition and dissipation are key to the identification of sites and mechanisms for drug action.

Molecular insights into atypical modes of β-arrestin interaction with seven transmembrane receptors

β-arrestins (βarrs) are multifunctional proteins involved in signaling and regulation of seven transmembrane receptors (7TMRs), and their interaction is driven primarily by agonist-induced receptor activation and phosphorylation. Here, we present seven cryo-electron microscopy structures of βarrs either in the basal state, activated by the muscarinic receptor subtype 2 (M2R) through its third intracellular loop, or activated by the βarr-biased decoy D6 receptor (D6R). Combined with biochemical, cellular, and biophysical experiments, these structural snapshots allow the visualization of atypical engagement of βarrs with 7TMRs and also reveal a structural transition in the carboxyl terminus of βarr2 from a β strand to an α helix upon activation by D6R. Our study provides previously unanticipated molecular insights into the structural and functional diversity encoded in 7TMR-βarr complexes with direct implications for exploring novel therapeutic avenues.

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 β-arrestin (βarr) recruitment and trafficking. For several GPCRs such as the vasopressin receptor subtype 2 (V₂R), agonist-stimulation first drives the translocation of βarrs to the plasma membrane, followed by endosomal trafficking, which is generally considered to be orchestrated by multiple phosphorylation sites. We have previously shown that mutation of a single phosphorylation site in the V₂R (i.e., V₂R^T360A) results in near-complete loss of βarr translocation to endosomes despite robust recruitment to the plasma membrane, and compromised ERK1/2 activation. Here, we discover that a synthetic intrabody (Ib30), which selectively recognizes activated βarr1, efficiently rescues the endosomal trafficking of βarr1 and ERK1/2 activation for V₂R^T360A. Molecular dynamics simulations reveal that Ib30 enriches active-like βarr1 conformation with respect to the inter-domain rotation, and cellular assays demonstrate that it also enhances βarr1-β₂-adaptin interaction. Our data provide an experimental framework to positively modulate the receptor-transducer-effector axis for GPCRs using intrabodies, which can be potentially integrated in the paradigm of GPCR-targeted drug discovery.

G protein-coupled receptors (GPCRs) are integral membrane proteins and the largest class of drug targets in the human genome. Here, Baidya et al. show that a synthetic antibody can be used to modulate GPCR trafficking and signaling in live cells.

FPR2 DNA Aptamers for Targeted Therapy of Wound Repair

Chronic wounds represent a major health problem worldwide. Some of the available therapies based on recombinant proteins usually fail owing to the hostile environment found at the wound bed. Aptamers appear as an attractive alternative to recombinant factors owing in part to their stability, sensitivity, specificity, and low-cost production. In this study, the Cell-Systematic Evolution of Ligands by EXponential Enrichment technology was employed to generate aptamers that specifically recognize and modulate the function of the FPR2, a receptor expressed in a variety of cells involved in wound repair. Three aptamers were obtained that specifically bound to FPR2 stable transfectants generated in HaCaT cells. The targeted aptamers were shown to act as FPR2 agonists in different in vitro functional assays, including wound healing assays, and elicited a similar pattern of response to that obtained with other known FPR2 peptide agonists, such as the human LL37 cathelicidin. We have also obtained in vivo evidence for the prohealing activities of one of these FPR2 aptamers in a skin-humanized mouse model developed by us, previously shown to accurately recreate the main phases of physiological human wound repair process. In conclusion, we provide evidence of the potential therapeutic value of FPR2 aptamers for cutaneous repair.

Emerging structural insights into GPCR-β-arrestin interaction and functional outcomes

Agonist-induced recruitment of β-arrestins (βarrs) to G protein-coupled receptors (GPCRs) plays a central role in regulating the spatio-temporal aspects of GPCR signaling. Several recent studies have provided novel structural and functional insights into our understanding of GPCR-βarr interaction, subsequent βarr activation and resulting functional outcomes. In this review, we discuss these recent advances with a particular emphasis on recognition of receptor-bound phosphates by βarrs, the emerging concept of spatial positioning of key phosphorylation sites, the conformational transition in βarrs during partial to full-engagement, and structural differences driving functional outcomes of βarr isoforms. We also highlight the key directions that require further investigation going forward to fully understand the structural mechanisms driving βarr activation and functional responses.

Suppression of tumor progression by thioredoxin-interacting protein-dependent adenosine 2B receptor degradation in a PLAG-treated Lewis lung carcinoma-1 model of non-small cell lung cancer

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PLAG effectively inhibited excessive growth of LLC1 cells in an NSCLC model.

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PLAG inhibited tumor growth by inducing adenosine 2B receptor (A2BR) degradation.

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Unlike antagonists, PLAG terminates rather than suppresses signaling pathways.

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A2BR degradation by PLAG occurs through expression and re-localization of TXNIP.

Extracellular adenosine in the tumor microenvironment plays a vital role in cancer development. Specifically, activation of adenosine receptors affects tumor cell growth and adenosine release.

We examined the anti-tumor efficacy of 1-palmitoyl-2-linoleoyl-3-acetyl-rac-glycerol (PLAG) in animal models, revealing the role of PLAG in inhibiting tumor progression by promoting the degradation of adenosine 2B receptors (A2BRs) in tumors. PLAG induced the expression of thioredoxin-interacting protein (TXNIP), a type of α-arrestin that accelerates A2BR internalization by interacting with A2BR complexes containing β-arrestin. Engulfed receptors bound to TXNIP were rapidly degraded after E3 ligase recruitment and ubiquitination, resulting in early termination of intracellular signals that promote tumor overgrowth. However, in control cancer cells, A2BRs bound to protein phosphatase 2A and were returned to the cell membrane instead of being degraded, resulting in continuous receptor-mediated signaling by pathways including the Raf-Erk axis, which promotes tumor proliferation. A TXNIP-silenced cell-implanted mouse model and TXNIP knockout (KO) mice were used to verify that PLAG-mediated suppression of tumor progression is dependent on TXNIP expression. Increased tumor growth was observed in TXNIP-silenced cell-implanted mice, and the anti-tumor effects of PLAG, including delayed tumor overgrowth, were greatly reduced. However, the anti-tumor effects of PLAG were observed in cancer cell-implanted TXNIP-KO mice, which indicates that PLAG produces anti-tumor effects by enhancing TXNIP expression in tumor cells.

These essential functions of PLAG, including delaying tumor growth via A2BR degradation, suggest innovative directions for anticancer drug development.

QR code model: a new possibility for GPCR phosphorylation recognition

G protein-coupled receptors (GPCRs) are the largest family of membrane proteins in the human body and are responsible for accurately transmitting extracellular information to cells. Arrestin is an important member of the GPCR signaling pathway. The main function of arrestin is to assist receptor desensitization, endocytosis and signal transduction. In these processes, the recognition and binding of arrestin to phosphorylated GPCRs is fundamental. However, the mechanism by which arrestin recognizes phosphorylated GPCRs is not fully understood. The GPCR phosphorylation recognition "bar code model" and "flute" model describe the basic process of receptor phosphorylation recognition in terms of receptor phosphorylation sites, arrestin structural changes and downstream signaling. These two models suggest that GPCR phosphorylation recognition is a process involving multiple factors. This process can be described by a "QR code" model in which ligands, GPCRs, G protein-coupled receptor kinase, arrestin, and phosphorylation sites work together to determine the biological functions of phosphorylated receptors. Video Abstract.

Nitric Oxide and S-Nitrosylation in Cardiac Regulation: G Protein-Coupled Receptor Kinase-2 and β-Arrestins as Targets

Cardiac diseases including heart failure (HF), are the leading cause of morbidity and mortality globally. Among the prominent characteristics of HF is the loss of β-adrenoceptor (AR)-mediated inotropic reserve. This is primarily due to the derangements in myocardial regulatory signaling proteins, G protein-coupled receptor (GPCR) kinases (GRKs) and β-arrestins (β-Arr) that modulate β-AR signal termination via receptor desensitization and downregulation. GRK2 and β-Arr2 activities are elevated in the heart after injury/stress and participate in HF through receptor inactivation. These GPCR regulators are modulated profoundly by nitric oxide (NO) produced by NO synthase (NOS) enzymes through S-nitrosylation due to receptor-coupled NO generation. S-nitrosylation, which is NO-mediated modification of protein cysteine residues to generate an S-nitrosothiol (SNO), mediates many effects of NO independently from its canonical guanylyl cyclase/cGMP/protein kinase G signaling. Herein, we review the knowledge on the NO system in the heart and S-nitrosylation-dependent modifications of myocardial GPCR signaling components GRKs and β-Arrs.

β-Arrestin-2 attenuates hepatic ischemia-reperfusion injury by activating PI3K/Akt signaling

Hepatic ischemia-reperfusion injury (IRI) remains a common complication during liver transplantation (LT), partial hepatectomy and hemorrhagic shock in patients. As a member of the G protein-coupled receptors adaptors, ARRB2 has been reported to be involved in a variety of physiological and pathological processes. However, whether β-arrestin-2 affects the pathogenesis of hepatic IRI remains unknown. The goal of the present study was to determine whether ARRB2 protects against hepatic IR injury and elucidate the underlying mechanisms. To this end, 70% hepatic IR models were established in ARRB2 knockdown mice and wild-type littermates, with blood and liver samples collected at 1, 6 and 12 h after reperfusion to evaluate liver injury. The effect of ARBB2 on PI3K/Akt signaling during IR injury was evaluated in vivo, and PI3K/Akt pathway regulation by ARRB2 was further assessed in vitro. Our results showed that ARRB2 knockdown aggravates hepatic IR injury by promoting the apoptosis of hepatocytes and inhibiting their proliferation. In addition, ARRB2 deficiency inhibited PI3K/Akt pathway activation, while the administration of the PI3K/Akt inhibitor PX866 resulted in severe IR injury in mice. Furthermore, the liver-protecting effect of ARRB2 was shown to depend on PI3K/Akt pathway activation. In summary, our results suggest that β-Arrestin-2 protects against hepatic IRI by activating PI3K/Akt signaling, which may provide a novel therapeutic strategy for treating liver ischemia-reperfusion injury.

G Protein-Coupled Receptor Kinase 2 (GRK2) as a Potential Therapeutic Target in Cardiovascular and Metabolic Diseases

G protein-coupled receptor kinase 2 (GRK2) is a central signaling node involved in the modulation of many G protein-coupled receptors (GPCRs) and also displaying regulatory functions in other cell signaling routes. GRK2 levels and activity have been reported to be enhanced in patients or in preclinical models of several relevant pathological situations, such as heart failure, cardiac hypertrophy, hypertension, obesity and insulin resistance conditions, or non-alcoholic fatty liver disease (NAFLD), and to contribute to disease progression by a variety of mechanisms related to its multifunctional roles. Therefore, targeting GRK2 by different strategies emerges as a potentially relevant approach to treat cardiovascular disease, obesity, type 2 diabetes, or NAFLD, pathological conditions which are frequently interconnected and present as co-morbidities.

Measuring agonist-induced ERK MAP kinase phosphorylation for G-protein-coupled receptors

Agonist stimulation of G-protein-coupled receptors (GPCRs) typically results in phosphorylation and activation of ERK (Extracellular-signal Regulated Kinase) which is a member of MAP kinase (Mitogen-Activated Protein kinase) family. Detection of phosphorylated ERK1/2 MAP kinase has been widely used as readout of GPCR signaling in heterologous cells, primary cells, tissues and even in animal studies. ERK1/2 phosphorylation downstream of GPCRs is now well established to arise from the activation of both, the heterotrimeric G-proteins and β-arrestins (βarrs) with distinct spatio-temporal components. Here, we present a step-by-step protocol for measuring agonist-induced ERK1/2 MAP kinase activation downstream of GPCRs using standard Western blotting assay. Note: ERK1/2 is also referred to as p44/42 MAP kinase. ERK1 and ERK2 are same as Mitogen-Activated Protein Kinase 3 (MAP3) and Mitogen-Activated Protein Kinase 1 (MAP1), respectively.

CAPA periviscerokinin-mediated activation of MAPK/ERK signaling through Gq-PLC-PKC-dependent cascade and reciprocal ERK activation-dependent internalized kinetics of Bom-CAPA-PVK receptor 2

Bombyx mori neuropeptide G protein-coupled receptor (BNGR)-A27 is a specific receptor for B. mori capability (CAPA) periviscerokinin (PVK), that is, Bom-CAPA-PVK receptor 2. Upon stimulation of Bom-CAPA-PVK-1 or -PVK-2, Bom-CAPA-PVK receptor 2 significantly increases cAMP-response element-controlled luciferase activity and Ca²⁺ mobilization in a Gq inhibitor-sensitive manner. However, the underlying mechanism(s) for CAPA/CAPA receptor system mediation of extracellular signal-regulated kinases1/2 (ERK1/2) activation remains to be explained further. Here, we discovered that Bom-CAPA-PVK receptor 2 stimulated ERK1/2 phosphorylation in a dose- and time-dependent manner in response to Bom-CAPA-PVK-1 or -PVK-2 with similar potencies. Furthermore, ERK1/2 phosphorylation can be inhibited by Gq inhibitor UBO-QIC, PLC inhibitor U73122, protein kinase C (PKC) inhibitor Go 6983, phospholipase D (PLD) inhibitor FIPI and Ca²⁺ chelators EGTA and BAPTA-AM. Moreover, Bom-CAPA-PVK-R2-induced activation of ERK1/2 was significantly attenuated by treatment with the Gβγ-specific inhibitors, phosphatidylinositol 3-kinase (PI3K)-specific inhibitor Wortmannin and Src-specific inhibitor PP2. Our data also demonstrate that receptor tyrosine kinase (RTK) transactivation pathways are involved in the mechanisms of Bom-CAPA-PVK receptor to ERK1/2 phosphorylation. In addition, β-arrestin1/2 is not involved in Bom-CAPA-PVK-R2-mediated ERK1/2 activation but required for the agonist-independent, ERK1/2 activation-dependent internalization of the G protein-coupled receptor (GPCR).

Optical approaches for visualization of arrestin binding to muscarinic receptor

G protein-coupled seven-transmembrane receptors (GPCRs) mediate responses to hormones, metabolites, lipids, and neurotransmitters at the cell membrane, and so they are prominent drug targets. Although many structural, biochemical, cell biological, and biophysical studies made remarkable progress to understand mechanisms of GPCR signaling, there still are many unanswered questions about arrestin-dependent GPCR signaling. In this chapter, we focus on optical assays to see muscarinic receptor-arrestin interactions with ensemble FRET and single-molecule TIRF imaging in live cells and finally to integrate the information to simulate hypothesized steps in Virtual Cell.

A synthetic intrabody-based selective and generic inhibitor of GPCR endocytosis

Beta-arrestins (βarrs) critically mediate desensitization, endocytosis and signalling of G protein-coupled receptors (GPCRs), and they scaffold a large number of interaction partners. However, allosteric modulation of their scaffolding abilities and direct targeting of their interaction interfaces to modulate GPCR functions selectively have not been fully explored yet. Here we identified a series of synthetic antibody fragments (Fabs) against different conformations of βarrs from phage display libraries. Several of these Fabs allosterically and selectively modulated the interaction of βarrs with clathrin and ERK MAP kinase. Interestingly, one of these Fabs selectively disrupted βarr-clathrin interaction, and when expressed as an intrabody, it robustly inhibited agonist-induced endocytosis of a broad set of GPCRs without affecting ERK MAP kinase activation. Our data therefore demonstrate the feasibility of selectively targeting βarr interactions using intrabodies and provide a novel framework for fine-tuning GPCR functions with potential therapeutic implications.

The role and mechanism of β‑arrestins in cancer invasion and metastasis (Review)

β-arrestins are a family of adaptor proteins that regulate the signaling and trafficking of various G protein-coupled receptors (GPCRs). They consist of β-arrestin1 and β-arrestin2 and are considered to be scaffolding proteins. β-arrestins regulate cell proliferation, promote cell invasion and migration, transmit anti-apoptotic survival signals and affect other characteristics of tumors, including tumor growth rate, angiogenesis, drug resistance, invasion and metastatic potential. It has been demonstrated that β-arrestins serve roles in various physiological and pathological processes and exhibit a similar function to GPCRs. β-arrestins serve primary roles in cancer invasion and metastasis via various signaling pathways. The present review assessed the function and mechanism of β-arrestins in cancer invasion and metastasis via multiple signaling pathways, including mitogen-activated protein kinase/extracellular signal regulated kinase, Wnt/β-catenin, nuclear factor-κB and phosphoinositide-3 kinase/Akt.

Systemic Sympathoexcitation Was Associated with Paraventricular Hypothalamic Phosphorylation of Synaptic CaMKIIα and MAPK/ErK

Systemic administration of adrenergic agonist (Isoproterenol; ISOP) is known to facilitate cardiovascular changes associated with heart failure through an upregulation of cardiac toll-like receptor 4 (TLR4). Furthermore, previous studies have shown that cardiac tissue-specific deletion of TLR4 protects the heart against such damage. Since the autonomic regulation of systemic cardiovascular function originates from pre-autonomic sympathetic centers in the brain, it is unclear how a systemically driven sympathetic change may affect the pre-autonomic paraventricular hypothalamic nuclei (PVN) TLR4 expression. Here, we examined how change in PVN TLR4 was associated with alterations in the neurochemical cytoarchitecture of the PVN in systemic adrenergic activation. After 48 h of intraperitoneal 150 mg/kg ISOP treatment, there was a change in PVN CaMKIIα and MAPK/ErK expression, and an increase in TLR4 in expression. This was seen as an increase in p-MAPK/ErK, and a decrease in synaptic CaMKIIα expression in the PVN (p < 0.01) of ISOP treated mice. Furthermore, there was an upregulation of vesicular glutamate transporter (VGLUT 2; p < 0.01) and a decreased expression of GABA in the PVN of Isoproterenol (ISOP) treated WT mice (p < 0.01). However, after a PVN-specific knockdown of TLR4, the effect of systemic administration of ISOP was attenuated, as indicated by a decrease in p-MAPK/ErK (p < 0.01) and upregulation of CaMKIIα (p < 0.05). Additionally, loss of inhibitory function was averted while VGLUT2 expression decreased when compared with the ISOP treated wild type mice and the control. Taken together, the outcome of this study showed that systemic adrenergic activation may alter the expression, and phosphorylation of preautonomic MAPK/ErK and CaMKIIα downstream of TLR4. As such, by outlining the roles of these kinases in synaptic function, we have identified the significance of neural TLR4 in the progression, and attenuation of synaptic changes in the pre-autonomic sympathetic centers.

Muscarinic receptor regulates extracellular signal regulated kinase by two modes of arrestin binding

Binding of agonists to G-protein-coupled receptors (GPCRs) activates heterotrimeric G proteins and downstream signaling. Agonist-bound GPCRs are then phosphorylated by protein kinases and bound by arrestin to trigger desensitization and endocytosis. Arrestin plays another important signaling function. It recruits and regulates activity of an extracellular signal-regulated kinase (ERK) cascade. However, molecular details and timing of ERK activation remain fundamental unanswered questions that limit understanding of how arrestin-dependent GPCR signaling controls cell functions. Here we validate and model a system that tracks the dynamics of interactions of arrestin with receptors and of ERK activation using optical reporters. Our intermolecular FRET measurements in living cells are consistent with β-arrestin binding to M₁ muscarinic acetylcholine receptors (M₁Rs) in two different binding modes, transient and stable. The stable mode persists for minutes after agonist removal. The choice of mode is governed by phosphorylation on key residues in the third intracellular loop of the receptor. We detect a similar intramolecular conformational change in arrestin in either binding mode. It develops within seconds of arrestin binding to the M₁ receptor, and it reverses within seconds of arrestin unbinding from the transient binding mode. Furthermore, we observed that, when stably bound to phosphorylated M₁R, β-arrestin scaffolds and activates MEK-dependent ERK. In contrast, when transiently bound, β-arrestin reduces ERK activity via recruitment of a protein phosphatase. All this ERK signaling develops at the plasma membrane. In this scaffolding hypothesis, a shifting balance between the two arrestin binding modes determines the degree of ERK activation at the membrane.

Novel Structural Insights into GPCR-β-Arrestin Interaction and Signaling

G protein-coupled receptors (GPCRs) are major signal recognition and transmission units in the plasma membrane. The interaction of activated and phosphorylated GPCRs with the multifunctional adaptor proteins β-arrestins (βarrs) is crucial for regulation of their signaling and functional outcomes. Over the past few years, a range of structural, biochemical, and cellular studies have revealed novel insights into GPCR-βarr interaction and signaling. Some of these findings have come as a surprise and therefore have the potential to significantly refine the conceptual framework of the GPCR-βarr system. Here we discuss these recent advances with particular emphasis on biphasic GPCR-βarr interaction, the formation of GPCR-G-protein-βarr supercomplexes, and receptor-specific conformational signatures in βarrs. We also underline the emerging research areas that are likely to be at the center stage of investigations in the coming years.

Scavenger Receptor C Mediates Phagocytosis of White Spot Syndrome Virus and Restricts Virus Proliferation in Shrimp

Scavenger receptors are an important class of pattern recognition receptors that play several important roles in host defense against pathogens. The class C scavenger receptors (SRCs) have only been identified in a few invertebrates, and their role in the immune response against viruses is seldom studied. In this study, we firstly identified an SRC from kuruma shrimp, Marsupenaeus japonicus, designated MjSRC, which was significantly upregulated after white spot syndrome virus (WSSV) challenge at the mRNA and protein levels in hemocytes. The quantity of WSSV increased in shrimp after knockdown of MjSRC, compared with the controls. Furthermore, overexpression of MjSRC led to enhanced WSSV elimination via phagocytosis by hemocytes. Pull-down and co-immunoprecipitation assays demonstrated the interaction between MjSRC and the WSSV envelope protein. Electron microscopy observation indicated that the colloidal gold-labeled extracellular domain of MjSRC was located on the outer surface of WSSV. MjSRC formed a trimer and was internalized into the cytoplasm after WSSV challenge, and the internalization was strongly inhibited after knockdown of Mjβ-arrestin2. Further studies found that Mjβ-arrestin2 interacted with the intracellular domain of MjSRC and induced the internalization of WSSV in a clathrin-dependent manner. WSSV were co-localized with lysosomes in hemocytes and the WSSV quantity in shrimp increased after injection of lysosome inhibitor, chloroquine. Collectively, this study demonstrated that MjSRC recognized WSSV via its extracellular domain and invoked hemocyte phagocytosis to restrict WSSV systemic infection. This is the first study to report an SRC as a pattern recognition receptor promoting phagocytosis of a virus.

Shrimp aquaculture is a major industry in many coastal countries, where it contributes significantly to socio-economic development. However, during the rapid expansion of shrimp industry, a succession of previously unknown diseases, especially viral diseases, have emerged in farmed shrimp and spread rapidly across international boundaries, which have significant effects on shrimp production. Since 1994, it has been estimated that annual losses globally caused by viral diseases have been as high as $US3 billion. White spot syndrome, caused by white spot syndrome virus (WSSV), is the most serious disease in shrimp aquaculture. Here, we reveal that a scavenger receptor in kuruma shrimp, Marsupenaeus japonicus (MjSRC) functions as the pattern recognition receptor for WSSV. MjSRC binds to WSSV and initiates phagocytosis of the virus, ultimately leading to degradation of WSSV in the lysosomes of hemocytes. This is the first report of the MjSRC antiviral mechanism, which may be used as a control strategy to prevent WSSV infection in shrimp.

Functional competence of a partially engaged GPCR-β-arrestin complex

G Protein-coupled receptors (GPCRs) constitute the largest family of cell surface receptors and drug targets. GPCR signalling and desensitization is critically regulated by β-arrestins (βarr). GPCR-βarr interaction is biphasic where the phosphorylated carboxyl terminus of GPCRs docks to the N-domain of βarr first and then seven transmembrane core of the receptor engages with βarr. It is currently unknown whether fully engaged GPCR-βarr complex is essential for functional outcomes or partially engaged complex can also be functionally competent. Here we assemble partially and fully engaged complexes of a chimeric β2V2R with βarr1, and discover that the core interaction is dispensable for receptor endocytosis, ERK MAP kinase binding and activation. Furthermore, we observe that carvedilol, a βarr biased ligand, does not promote detectable engagement between βarr1 and the receptor core. These findings uncover a previously unknown aspect of GPCR-βarr interaction and provide novel insights into GPCR signalling and regulatory paradigms.