Biology subjects

Shen, D.-D.

Publications and source records attributed to Shen, D.-D..

7 recordsLinked to original sources

bioRxiv2024

Structural Basis of GPCR-G Protein Pre-coupling and Activation: Insights from CCR1-Gi Complex

GPCR-mediated G protein activation cycle contains obligated step of the receptor-G protein assembly before G protein activation (pre-coupling state). However, transient nature of this pre-coupling state has prevented structural and mechanistic understanding of this essential step of G protein activation cycle. In this study, we discover that CCR1 has high level of pre-coupling state, which allows its rapid response to chemokines. Taking advantage of this observation, we uncover molecular mechanism of the pre-coupling state by solving the cryo-electron microscopy structure of the chemokine receptor CCR1 in complex with its cognate G protein (Gi) in a pre-coupled, inactivated state. This structure reveals that CCR1 adopts a conformation distinct from both its fully active and inactive states, with the G proteins 5 helix partially inserted into the receptors intracellular cavity. Notably, the C-terminal four residues of the G subunit are disordered in this pre-coupled state, contrasting with their well-defined -helical structure in the fully active complex. Functional assays demonstrate that while deletion of these four C-terminal G residues does not affect pre-coupling, it abolishes G protein activation upon agonist binding. This finding highlights the critical role of these residues in GPCR-mediated G protein activation, but not in initial recruitment. Furthermore, our studies indicate that the ability to form pre-coupled complexes is conserved among chemokine receptors, suggesting a common mechanism for rapid signal transduction in this GPCR subfamily. These results provide the first structural evidence for GPCR-G protein pre-coupling and offer molecular insights into the transition from inactive to active states. Our findings fill the long-missing gap in understanding GPCR-mediated G protein activated cycle.

biophysics↗

bioRxiv2022

Molecular basis for allosteric agonism and G protein subtype selectivity of galanin receptors

Peptide hormones and neuropeptides are complex signaling molecules that predominately function through G protein-coupled receptors (GPCRs). Two fundamental questions remained in the field of peptide-GPCR signaling systems are the basis for the diverse binding mode of peptide ligands and the specificity of G protein coupling. Here we report the structures of a neuropeptide, galanin, bound to its receptors, GAL1R and GAL2R, in complex with their primary G protein subtypes Gi and Gq, respectively. The structures reveal a unique binding pose of galanin, which almost lay flat on the top of the receptor transmembrane domain pocket in an -helical conformation, and acts as an allosteric-like agonist via a distinct signal transduction cascade. The structures also uncover the important features of intracellular loop 2 (ICL2) that mediate specific interactions with Gq, thus determining the selective coupling of Gq to GAL2R. ICL2 replacement in Gi-coupled GAL1R, OR, 5-HT1AR, and Gs-coupled b2AR and D1R with that of GAL2R promotes Gq coupling of these receptors, highlighting the dominant roles of ICL2 in Gq selectivity. Together our results provide important insights into peptide ligand recognition and allosteric activation of galanin receptors and uncover a general structural element for Gq coupling selectivity.

molecular biology↗

bioRxiv2021

Structural insights into ligand recognition and activation of the melanocortin-4 receptor

Melanocortin-4 receptor (MC4R) plays a central role in the regulation of energy homeostasis. Its high sequence similarity to other MC receptor family members, low agonist selectivity and the lack of structural information concerning receptor activation have hampered the development of MC4R-seletive therapeutics to treat obesity. Here, we report four high-resolution structures of full-length MC4R in complex with the heterotrimeric Gs protein stimulated by the endogenous peptide -MSH, FDA-approved drugs afamelanotide (Scenesse) and bremelanotide (Vyleesi), and selective small-molecule ligand THIQ, respectively. Together with pharmacological studies, our results reveal the conserved binding mode of peptidic agonists, the distinctive molecular details of small-molecule agonist recognition underlying receptor subtype selectivity, and distinct activation mechanism for MC4R, thereby offering new insights into G protein coupling. Our work may facilitate the discovery of selective therapeutic agents targeting MC4R.

molecular biology↗

bioRxiv2021

Structural insights into hormone recognition by the human glucose-dependent insulinotropic polypeptide receptor

Glucose-dependent insulinotropic polypeptide (GIP) is a peptide hormone that exerts crucial metabolic functions by binding and activating its cognate receptor, GIPR. As an important therapeutic target, GIPR has been subjected to intensive structural studies without success. Here, we report the cryo-EM structure of the human GIPR in complex with GIP and a Gs heterotrimer at a global resolution of 2.9 [A]. GIP adopts a single straight helix with its N terminus dipped into the receptor transmembrane domain (TMD), while the C-terminus is closely associated with the extracellular domain and extracellular loop 1. GIPR employs conserved residues in the lower half of the TMD pocket to recognize the common segments shared by GIP homologous peptides, while uses non-conserved residues in the upper half of the TMD pocket to interact with residues specific for GIP. These results provide a structural framework of hormone recognition and GIPR activation.

molecular biology↗

bioRxiv2020

Structural basis of bile acid receptor activation and Gs coupling

G protein-coupled bile acid receptor (GPBAR) is a membrane receptor that senses bile acids to regulate diverse functions through Gs activation. Here, we report the cryo-EM structures of GPBAR-Gs complexes stabilized by either high-affinity P395 or the semisynthesized bile acid derivative INT-777 at 3-[A] resolution. These structures revealed a large oval-shaped ligand pocket with several sporadic polar groups to accommodate the amphipathic cholic core of bile acids. A fingerprint of key residues recognizing diverse bile acids in the orthosteric site, a putative second bile acid binding site with allosteric properties and structural features contributing to bias property were identified through structural analysis and mutagenesis studies. Moreover, structural comparison of GPBAR with other GPCRs uncovered an atypical mode of receptor activation and G-protein- coupling, featuring a different set of key residues connecting the ligand binding pocket to the Gs coupling site, and a specific interaction motif localized in intracellular loop 3. Overall, our study not only provides unique structural features of GPBAR in bile acid recognition, allosteric effects and biased signaling, but also suggests that distinct allosteric connecting mechanisms between the ligand binding pocket and the G protein binding site exist in the GPCR superfamily.

biochemistry↗

bioRxiv2020

Cryo-EM structures of inactive and Gi-coupled GABAB heterodimer

Metabotropic GABAB G protein-coupled receptor functions as a mandatory heterodimer of GB1 and GB2 subunits and mediates inhibitory neurotransmission in the central nervous system. Each subunit is composed of the extracellular Venus flytrap (VFT) domain and transmembrane (TM) domain. Here we present cryo-EM structures of human full-length heterodimeric GABAB receptor in the antagonist-bound inactive state and in the active state complexed with agonist and positive allosteric modulator in the presence of Gi1 protein at a resolution range of 2.8-3.0 [A]. Cryo-EM analysis of the activated-GABAB-Gi1 complex revealed that Gi1 couples to the activated receptor primarily in three major conformations, one via GB1 TM and two via GB2 TM, respectively. Our structures reveal that agonist binding stabilizes the closure of GB1 VFT, which in turn triggers a rearrangement of TM interfaces between two subunits from TM3-TM5/TM3-TM5 in the inactive state to TM6/TM6 in the active state and finally induces the opening of intracellular loop 3 and synergistically shifting of TM3, 4 and 5 helices in GB2 TM domain to accommodate the 5-helix of Gi1. These results provide a structural framework for understanding class C GPCR activation and a rational template for allosteric modulator design targeting dimeric interface of GABAB receptor.

molecular biology↗

bioRxiv2020

Structural Basis for the Inhibition of the RNA-Dependent RNA Polymerase from SARS-CoV-2 by Remdesivir

The pandemic of Corona Virus Disease 2019 (COVID-19) caused by SARS-CoV-2 has become a global crisis. The replication of SARS-CoV-2 requires the viral RNA-dependent RNA polymerase (RdRp), a direct target of the antiviral drug, Remdesivir. Here we report the structure of the SARS-CoV-2 RdRp either in the apo form or in complex with a 50-base template-primer RNA and Remdesivir at a resolution range of 2.5-2.8 [A]. The complex structure reveals that the partial double-stranded RNA template is inserted into the central channel of the RdRp where Remdesivir is incorporated into the first replicated base pair and terminates the chain elongation. Our structures provide critical insights into the working mechanism of viral RNA replication and a rational template for drug design to combat the viral infection.

molecular biology↗