Mechanistic insights into G-protein coupling with an agonist-bound G-protein-coupled receptor

G-protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by promoting guanine nucleotide exchange. Here, we investigate the coupling of G proteins with GPCRs and describe the events that ultimately lead to the ejection of GDP from its binding pocket in the Gα subunit, the rate-limiting step during G-protein activation. Using molecular dynamics simulations, we investigate the temporal progression of structural rearrangements of GDP-bound Gs protein (Gs·GDP; hereafter GsGDP) upon coupling to the β2-adrenergic receptor (β2AR) in atomic detail. The binding of GsGDP to the β2AR is followed by long-range allosteric effects that significantly reduce the energy needed for GDP release: the opening of α1-αF helices, the displacement of the αG helix and the opening of the α-helical domain. Signal propagation to the Gs occurs through an extended receptor interface, including a lysine-rich motif at the intracellular end of a kinked transmembrane helix 6, which was confirmed by site-directed mutagenesis and functional assays. From this β2AR-GsGDP intermediate, Gs undergoes an in-plane rotation along the receptor axis to approach the β2AR-Gsempty state. The simulations shed light on how the structural elements at the receptor-G-protein interface may interact to transmit the signal over 30 Å to the nucleotide-binding site. Our analysis extends the current limited view of nucleotide-free snapshots to include additional states and structural features responsible for signaling and G-protein coupling specificity.This work was funded by German Research Foundation (DFG) through CRC1423, project number 421152132, subproject C01 (to P.W.H.) and subprojects A01, A05 and Z03 (to P.S.), Stiftung Charité and the Einstein Center Digital for Future to P.W.H. P.S. is further supported through CRC 1078–Project ID 221545957–SFB 1078, subproject B06; through the cluster of excellence ‘UniSysCat‘ (under Germany’s Excellence Strategy-EXC2008/1-390540038 and through the European Union’s Horizon 2020 MSCA Program under grant agreement 956314 (ALLODD). This work was also funded by National Institutes of Health grant R01NS028471 (to B.K.K.), by National Natural Science Foundation of China (Grant 32122041 to X.L.) and by Tsinghua University Initiative Scientific Research Program (to X.L.). We are grateful to A. Inoue (Tohoku University, Japan) for providing the CRISPR–Cas9-edited triple knockout barr1/barr2/β2AR HEK293A cells and to H. Schihada (Philipps-Universität Marburg, Germany) for providing the Gs-CASE sensor DNA material and advice for the BRET dissociation assay. We thank B. Bauer (Charité–Universitätsmedizin Berlin, Germany) for assistance in molecular biology and purifying reagents. B.K.K. and P.W.H. acknowledge the Einstein Foundation and the Berlin Institute of Health for their support. We are grateful to M. Heck (Charité–Universitätsmedizin Berlin, Germany) for advice on the statistical analysis of the BRET 2 assay and M. Heck and K. P. Hofmann (Charité–Universitätsmedizin Berlin, Germany) for helpful discussions. P.F.S. also holds external affiliations with the Institute of Theoretical Chemistry, University of Vienna, Austria, the Universidad Nacional de Colombia, Bogotá, Colombia, the Center for noncoding RNA in Technology and Health at the University of Copenhagen and the Santa Fe Institute, Santa Fe, New Mexico, USA. We gratefully acknowledge the scientific support and HPC resources provided by the Erlangen National High Performance Computing Center (NHR@FAU) of the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) under the NHR project p101ae. NHR funding is provided by federal and Bavarian state authorities. NHR@FAU hardware is partially funded by DFG (440719683).Peer reviewe

G-protein activation by a metabotropic glutamate receptor

Family C G-protein-coupled receptors (GPCRs) operate as obligate dimers with extracellular domains that recognize small ligands, leading to G-protein activation on the transmembrane (TM) domains of these receptors by an unknown mechanism(1). Here we show structures of homodimers of the family C metabotropic glutamate receptor 2 (mGlu2) in distinct functional states and in complex with heterotrimeric G(i). Upon activation of the extracellular domain, the two transmembrane domains undergo extensive rearrangement in relative orientation to establish an asymmetric TM6–TM6 interface that promotes conformational changes in the cytoplasmic domain of one protomer. Nucleotide-bound G(i) can be observed pre-coupled to inactive mGlu2, but its transition to the nucleotide-free form seems to depend on establishing the active-state TM6–TM6 interface. In contrast to family A and B GPCRs, G-protein coupling does not involve the cytoplasmic opening of TM6 but is facilitated through the coordination of intracellular loops 2 and 3, as well as a critical contribution from the C terminus of the receptor. The findings highlight the synergy of global and local conformational transitions to facilitate a new mode of G-protein activation

Image_1_Protein phosphatase-1 inhibitor-2 promotes PP1γ positive regulation of synaptic transmission.tiff

Inhibitor-2 (I-2) is a prototypic inhibitor of protein phosphatase-1 (PP1), a major serine-threonine phosphatase that regulates synaptic plasticity and learning and memory. Although I-2 is a potent inhibitor of PP1 in vitro, our previous work has elucidated that, in vivo, I-2 may act as a positive regulator of PP1. Here we show that I-2 and PP1γ, but not PP1α, positively regulate synaptic transmission in hippocampal neurons. Moreover, we demonstrated that I-2 enhanced PP1γ interaction with its major synaptic scaffold, neurabin, by Förster resonance energy transfer (FRET)/Fluorescence lifetime imaging microscopy (FLIM) studies, while having a limited effect on PP1 auto-inhibitory phosphorylation. Furthermore, our study indicates that the effect of I-2 on PP1 activity in vivo is dictated by I-2 threonine-72 phosphorylation. Our work thus demonstrates a molecular mechanism by which I-2 positively regulates PP1 function in synaptic transmission.</p