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Nucleotide analog inhibitors, including broad-spectrum remdesivir and favipiravir, have shown promise in in vitro assays and some clinical studies for COVID-19 treatment, this despite an incomplete mechanistic understanding of the viral RNA-dependent RNA polymerase nsp12 drug interactions. Here, we examine the molecular basis of SARS-CoV-2 RNA replication by determining the cryo-EM structures of the stalled pre- and post- translocated polymerase complexes. Compared with the apo complex, the structures show notable structural rearrangements happening to nsp12 and its co-factors nsp7 and nsp8 to accommodate the nucleic acid, whereas there are highly conserved residues in nsp12, positioning the template and primer for an in-line attack on the incoming nucleotide. Furthermore, we investigate the inhibition mechanism of the triphosphate metabolite of remdesivir through structural and kinetic analyses. A transition model from the nsp7-nsp8 hexadecameric primase complex to the nsp12-nsp7-nsp8 polymerase complex is also proposed to provide clues for the understanding of the coronavirus transcription and replication machinery. • Structures of SARS-CoV-2 RNA polymerase in complexes with RNA revealed • Conformational changes in nsp8 and its interaction with the exiting RNA are observed • Incorporation and delayed-chain-termination mechanism of remdesivir is elucidated • Transition model from primase complex to polymerase complex is proposed Cryo-EM structures of the SARS-CoV-2 RNA polymerase in complexes with RNA, before and after RNA translocation, reveals structural rearrangements that the RNA-dependent RNA polymerase (RdRp) nsp12 and its co-factors (nsp7 and nsp8) undergo to accommodate nucleic acid binding. Further insights into how the complex is inhibited by remdesivir, and into the primase to polymerase transition, are also presented. [ABSTRACT FROM AUTHOR]

Human endocannabinoid systems modulate multiple physiological processes mainly through the activation of cannabinoid receptors CB1 and CB2. Their high sequence similarity, low agonist selectivity, and lack of activation and G protein-coupling knowledge have hindered the development of therapeutic applications. Importantly, missing structural information has significantly held back the development of promising CB2-selective agonist drugs for treating inflammatory and neuropathic pain without the psychoactivity of CB1. Here, we report the cryoelectron microscopy structures of synthetic cannabinoid-bound CB2 and CB1 in complex with G i , as well as agonist-bound CB2 crystal structure. Of important scientific and therapeutic benefit, our results reveal a diverse activation and signaling mechanism, the structural basis of CB2-selective agonists design, and the unexpected interaction of cholesterol with CB1, suggestive of its endogenous allosteric modulating role. • 3D structures of CB2-AM12033-G i , CB1-AM841-G i , and CB2-AM12033 are determined • Structural evidence of G protein selectivity by CB1 and CB2 is identified • MD simulations reveal the distinct binding behavior of HU308 in CB2 and CB1 • Cholesterol molecule as an endogenous allosteric modulator of CB1 is uncovered Structure and simulations of cannabinoid receptors CB2 and CB1 in their inactive, active-like, and activated signaling states reveal residue differences that may provide G protein selectivity, the distinct binding behavior of CB2 agonists in CB2 and CB1, as well as evidence for modulation of CB1 by cholesterol binding. [ABSTRACT FROM AUTHOR]

Adrenergic G-protein-coupled receptors (GPCRs) mediate different cellular signaling pathways in the presence of endogenous catecholamines and play important roles in both physiological and pathological conditions. Extensive studies have been carried out to investigate the structure and function of β adrenergic receptors (βARs). However, the structure of α adrenergic receptors (αARs) remains to be determined. Here, we report the structure of the human α 2C adrenergic receptor (α 2C AR) with the non-selective antagonist, RS79948, at 2.8 Å. Our structure, mutations, modeling, and functional experiments indicate that a α 2C AR-specific D206 ECL2 -R409 ECL3 -Y405 6.58 network plays a role in determining α 2 adrenergic subtype selectivity. Furthermore, our results show that a specific loosened helix at the top of TM4 in α 2C AR is involved in receptor activation. Together, our structure of human α 2C AR-RS79948 provides key insight into the mechanism underlying the α 2 adrenergic receptor activation and subtype selectivity., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)