Biology subjects

Tall, G. G.

Publications and source records attributed to Tall, G. G..

4 recordsLinked to original sources

bioRxiv2025

β-arrestin recruitment facilitates a direct association with G proteins

G protein-coupled receptors (GPCRs) are targets for almost a third of all FDA-approved drugs. GPCRs are known to signal through both heterotrimeric G proteins and {beta}-arrestins. Traditionally these pathways were viewed as largely separable, with G proteins primarily initiating downstream signaling while {beta}-arrestins modulate receptor trafficking and desensitization in addition to regulating their own signaling events. Recent studies suggest an integrated role of G proteins and {beta}-arrestins in GPCR signaling, however the cellular and biochemical requirements for G protein: {beta}-arrestin interactions remain unclear. Here we show that G proteins and {beta}-arrestins can directly interact. Through utilization of {beta}-arrestin-biased receptors and artificially enforced {beta}-arrestin relocalization, we demonstrate that recruitment of {beta}-arrestin to the plasma membrane is sufficient to interact with the G protein Gi. Using purified proteins, we show that Gi directly interacts with {beta}-arrestin. In addition, we find that Gi family members differ in their degree of association with {beta}-arrestin, and that a large degree of this selectivity resides within the alpha helical domain of Gi. These findings delineate the cellular and biochemical conditions that drive direct interactions between G proteins and {beta}-arrestins and illuminate the molecular basis for how they work together to effect GPCR signaling.

biochemistry↗

bioRxiv2024

Structural basis for catalysis and selectivity of phospholipid synthesis by eukaryotic choline-phosphotransferase

Phospholipids are the most abundant component in lipid membranes and are essential for the structural and functional integrity of the cell. In eukaryotic cells, phospholipids are primarily synthesized de novo through the Kennedy pathway that involves multiple enzymatic processes. The terminal reaction is mediated by a group of cytidine-5-diphosphate (CDP)-choline /CDP-ethanolamine-phosphotransferases (CPT/EPT) that use 1,2-diacylglycerol (DAG) and CDP-choline or CDP-ethanolamine to produce phosphatidylcholine (PC) or phosphatidylethanolamine (PE) those are the main phospholipids in eukaryotic cells. Here we present the structure of the yeast CPT1 in multiple substrate-bound states. Structural and functional analysis of these binding-sites reveal the critical residues for the DAG acyl-chain preference and the choline/ethanolamine selectivity. Additionally, we present the structure in complex with a potent inhibitor characterized in this study. The ensemble of structures allows us to propose the reaction mechanism for phospholipid biosynthesis by the family of CDP-alcohol phosphatidyltransferases (CDP-APs).

biochemistry↗

bioRxiv2020

Crystal and cryo-EM structures of the cytosolic G protein alpha chaperone and guanine nucleotide exchange factor Ric-8A bound to Gαi1

Ric-8A is a cytosolic Guanine Nucleotide exchange Factor (GEF) that activates heterotrimeric G protein alpha subunits (G)1. Ric-8A is essential to life in multicellular eukaryotes by virtue of its chaperone activity that is required for G biogenesis and membrane localization2, 3. Ric-8A adopts an armadillo (ARM)/HEAT repeat domain architecture and is structurally unrelated to G Protein-Coupled Receptors (GPCR)4. Both GEF and chaperone activities are stimulated by Casein Kinase II phosphorylation5. The mechanisms by which Ric-8A catalyzes GDP release and GTP binding to G, or exerts chaperone activity are unknown. Here, we report the structure of the nanobody-stabilized complex of nucleotide-free Gi1 (isoform 1 of G family i) and phosphorylated Ric-8A at near atomic resolution by cryo-electron microscopy and X-ray crystallography. We find that Ric-8A envelops the GTPase domain of G, disrupting all three switch regions that convey G nucleotide-binding and signaling activity, and displaces the C-terminal helix and helical domain of G. These cooperative interactions dismantle the GDP binding site and promote GDP release, while protecting structural elements of G that are dynamic in the nucleotide-free state. The structures also show how in vivo phosphorylation stabilizes G-binding elements of Ric-8A, thereby enhancing its GEF and chaperone activities.

biochemistry↗

bioRxiv2019

Activation of phospholipase C β by Gβγ and Gαq involves C-terminal rearrangement to release auto-inhibition

Phospholipase C (PLC) enzymes hydrolyse phosphoinositide lipids to inositol phosphates and diacylglycerol. Direct activation of PLC{beta} by Gq and/or G{beta}{gamma} subunits mediates signalling by Gq and some Gi coupled G protein-coupled receptors (GPCRs), respectively. PLC{beta} isoforms contain a unique C-terminal extension, consisting of proximal and distal C-terminal domains (CTD) separated by a flexible linker. The structure of PLC{beta}3 bound to Gq is known, however, for both Gq and G{beta}{gamma}, the mechanism for PLC{beta} activation on membranes is unknown. We examined PLC{beta}2 dynamics on membranes using hydrogen deuterium exchange mass spectrometry (HDX-MS). G{beta}{gamma} caused a robust increase in dynamics of the distal C-terminal domain (CTD). Gq showed decreased deuterium incorporation at the Gq binding site on PLC{beta}. In vitro G{beta}{gamma}-dependent activation of PLC is inhibited by the distal CTD. The results suggest that disruption of auto-inhibitory interactions with the CTD, respectively, leads to increased PLC{beta} hydrolase activity.

biochemistry↗