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Structure of rat beta-arrestin 1 by fiducial-assisted cryo-EM
Structural highlights
FunctionARRB1_RAT Functions in regulating agonist-mediated G-protein coupled receptor (GPCR) signaling by mediating both receptor desensitization and resensitization processes. During homologous desensitization, beta-arrestins bind to the GPRK-phosphorylated receptor and sterically preclude its coupling to the cognate G-protein; the binding appears to require additional receptor determinants exposed only in the active receptor conformation. The beta-arrestins target many receptors for internalization by acting as endocytic adapters (CLASPs, clathrin-associated sorting proteins) and recruiting the GPRCs to the adapter protein 2 complex 2 (AP-2) in clathrin-coated pits (CCPs). However, the extent of beta-arrestin involvement appears to vary significantly depending on the receptor, agonist and cell type. Internalized arrestin-receptor complexes traffic to intracellular endosomes, where they remain uncoupled from G-proteins. Two different modes of arrestin-mediated internalization occur. Class A receptors, like ADRB2, OPRM1, ENDRA, D1AR and ADRA1B dissociate from beta-arrestin at or near the plasma membrane and undergo rapid recycling. Class B receptors, like AVPR2, AGTR1, NTSR1, TRHR and TACR1 internalize as a complex with arrestin and traffic with it to endosomal vesicles, presumably as desensitized receptors, for extended periods of time. Receptor resensitization then requires that receptor-bound arrestin is removed so that the receptor can be dephosphorylated and returned to the plasma membrane. Involved in internalization of P2RY4 and UTP-stimulated internalization of P2RY2. Involved in phosphorylation-dependent internalization of OPRD1 ands subsequent recycling. Involved in the degradation of cAMP by recruiting cAMP phosphodiesterases to ligand-activated receptors. Beta-arrestins function as multivalent adapter proteins that can switch the GPCR from a G-protein signaling mode that transmits short-lived signals from the plasma membrane via small molecule second messengers and ion channels to a beta-arrestin signaling mode that transmits a distinct set of signals that are initiated as the receptor internalizes and transits the intracellular compartment. Acts as signaling scaffold for MAPK pathways such as MAPK1/3 (ERK1/2). ERK1/2 activated by the beta-arrestin scaffold is largely excluded from the nucleus and confined to cytoplasmic locations such as endocytic vesicles, also called beta-arrestin signalosomes. Recruits c-Src/SRC to ADRB2 resulting in ERK activation. GPCRs for which the beta-arrestin-mediated signaling relies on both ARRB1 and ARRB2 (codependent regulation) include ADRB2, F2RL1 and PTH1R. For some GPCRs the beta-arrestin-mediated signaling relies on either ARRB1 or ARRB2 and is inhibited by the other respective beta-arrestin form (reciprocal regulation). Inhibits ERK1/2 signaling in AGTR1- and AVPR2-mediated activation (reciprocal regulation). Is required for SP-stimulated endocytosis of NK1R and recruits c-Src/SRC to internalized NK1R resulting in ERK1/2 activation, which is required for the antiapoptotic effects of SP. Is involved in proteinase-activated F2RL1-mediated ERK activity. Acts as signaling scaffold for the AKT1 pathway. Is involved in alpha-thrombin-stimulated AKT1 signaling. Is involved in IGF1-stimulated AKT1 signaling leading to increased protection from apoptosis. Involved in activation of the p38 MAPK signaling pathway and in actin bundle formation. Involved in F2RL1-mediated cytoskeletal rearrangement and chemotaxis. Involved in AGTR1-mediated stress fiber formation by acting together with GNAQ to activate RHOA. Appears to function as signaling scaffold involved in regulation of MIP-1-beta-stimulated CCR5-dependent chemotaxis. Involved in attenuation of NF-kappa-B-dependent transcription in response to GPCR or cytokine stimulation by interacting with and stabilizing CHUK. May serve as nuclear messenger for GPCRs. Involved in OPRD1-stimulated transcriptional regulation by translocating to CDKN1B and FOS promoter regions and recruiting EP300 resulting in acetylation of histone H4. Involved in regulation of LEF1 transcriptional activity via interaction with DVL1 and/or DVL2 Also involved in regulation of receptors other than GPCRs. Involved in Toll-like receptor and IL-1 receptor signaling through the interaction with TRAF6 which prevents TRAF6 autoubiquitination and oligomerization required for activation of NF-kappa-B and JUN. Binds phosphoinositides. Binds inositolhexakisphosphate (InsP6) (By similarity). Involved in IL8-mediated granule release in neutrophils.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] C562_ECOLX Electron-transport protein of unknown function. Publication Abstract from PubMedbeta-arrestins (betaarrs) are key regulators of G protein-coupled receptors (GPCRs), essential for modulating signaling pathways and physiological processes. While current pharmacological strategies target GPCR orthosteric and allosteric sites, as well as G protein transducers, comparable tools for studying betaarrs are lacking. Here, we present the discovery and characterization of novel small-molecule allosteric inhibitors of betaarrs through comprehensive biophysical, biochemical, pharmacological, and structural analyses. These inhibitors disrupt betaarr interactions with agonist-activated GPCRs, impairing receptor internalization, desensitization, and betaarr-mediated physiological functions. A cryo-EM structure of betaarr1 in complex with the allosteric inhibitor Cmpd-5, complemented by molecular dynamics simulations and mutagenesis studies, reveals that Cmpd-5 binds within a cryptic cleft formed by the middle, C-, and lariat loops-a critical site for betaarr activation and recruitment to GPCRs. Thus, Cmpd-5 acts as a molecular lock, hindering betaarr1 activation via an allosteric mechanism. These findings introduce novel strategies and tools for probing betaarr functions. HIGHLIGHTS: Small molecule strategies for modulating betaarr functions in both GPCR-dependent and independent contexts.Modulators disrupt betaarr interaction with GPCRs, impairing their critical functions.Cryo-EM structures reveal the allosteric inhibitor Cmpd-5 binding to a cryptic pocket between the N and C domains in the central crest of betaarr1, inhibiting its activation.Structural analyses, including cryo-EM, MD simulations, and mutagenesis, reveal a unique betaarr1 conformation induced by Cmpd-5, shedding light on its mechanism of allosteric inhibition. Small Molecule Modulators of beta-arrestins.,Kahsai AW, Pakharukova N, Kwon HY, Shah KS, Liang-Lin JG, Del Real CT, Shim PJ, Lee MA, Ngo VA, Shreiber BN, Liu S, Schwalb AM, Espinoza EF, Thomas BN, Kunzle CA, Smith JS, Wang J, Kim J, Zhang X, Rockman HA, Thomsen ARB, Rein LAM, Shi L, Ahn S, Masoudi A, Lefkowitz RJ bioRxiv [Preprint]. 2024 Dec 27:2024.12.27.630464. doi: , 10.1101/2024.12.27.630464. PMID:39763753[21] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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