G protein-coupled receptors (GPCRs), especially the class A, are the most heavily investigated drug targets in the pharmaceutical industry. Tremendous efforts have been made by both industry and ...academia to understand the molecular structure and function of this large family of transmembrane proteins. Our understanding in GPCR activation has evolved from the classical inactive-active two-state model to a complex view of GPCR conformational ensemble associated with multiple interacting partners such as ligands, allosteric modulators, ions and downstream signaling proteins. New drug targets and ligand design strategies are unveiled. Meanwhile, breakthroughs in X-ray crystallography have resulted in high-resolution structures of over 30 GPCRs, providing structural basis for drug design and functional studies. These enabled wide applications of computational approaches in GPCR research that have led to several groundbreaking studies in the last few years. While a large fraction of human GPCRs has yet to be crystallized, homology modeling plays a pivotal role in the simulation of these GPCRs. Here, we review the recent updates on class A GPCR structure and function, with a focus on the applications and perspectives of molecular modeling in GPCR ligand design.
Ceramide transfer protein (CERT) mediates non‐vesicular transfer of ceramide from endoplasmic reticulum to Golgi apparatus and thus catalyzes the rate‐limiting step of sphingomyelin biosynthesis. ...Usually, CERT ligands are evaluated in tedious binding assays or non‐homogenous transfer assays using radiolabeled ceramides. Herein, a facile and sensitive assay for CERT, based on Förster resonance energy transfer (FRET), is presented. To this end, we mixed donor and acceptor vesicles, each containing a different fluorescent ceramide species. By CERT‐mediated transfer of fluorescent ceramide, a FRET system was established, which allows readout in 96‐well plate format, despite the high hydrophobicity of the components. Screening of a 2 000 compound library resulted in two new potent CERT inhibitors. One is approved for use in humans and one is approved for use in animals. Evaluation of cellular activity by quantitative mass spectrometry and confocal microscopy showed inhibition of ceramide trafficking and sphingomyelin biosynthesis.
FRET indicates lipid transfer: A new FRET‐based lipid‐transfer assay was developed and used to screen a 2 000 member library for inhibitors of the sphingolipid transporter CERT. Hits were confirmed by different assays and used to induce sphingolipid trafficking phenotypes in living cells.
Mammals recognize chemicals in the air via G protein-coupled odorant receptors (ORs). In addition to their orthosteric binding site, other segments of these receptors modulate ligand recognition. ...Focusing on human hOR1A1, which is considered prototypical of class II ORs, we used a combination of molecular modeling, site-directed mutagenesis, and in vitro functional assays. We showed that the third extracellular loop of ORs (ECL3) contributes to ligand recognition and receptor activation. Indeed, site-directed mutations in ECL3 showed differential effects on the potency and efficacy of both carvones, citronellol, and 2-nonanone.
The fish olfactory receptor ORA family is orthologous to the mammalian vomeronasal receptors type 1. It consists of six highly conserved chemosensory receptors expected to be essential for survival ...and communication. We deorphanized the zebrafish ORA family in a heterologous cell system. The six receptors responded specifically to lithocholic acid (LCA) and closely related C24 5β-bile acids/salts. LCA attracted zebrafish as strongly as food in behavioral tests, whereas the less potent cholanic acid elicited weaker attraction, consistent with the in vitro results. The ORA-ligand recognition patterns were probed with site-directed mutagenesis guided by in silico modeling. We revealed the receptors’ structure–function relationship underlying their specificity and selectivity for these compounds. Bile acids/salts are putative fish semiochemicals or pheromones sensed by the olfactory system with high specificity. This work identified their receptors and provided the basis for probing the roles of ORAs and bile acids/salts in fish chemosensation.
(SA) leukocidin ED (LukED) belongs to a family of bicomponent pore forming toxins that play important roles in SA immune evasion and nutrient acquisition. LukED targets specific G protein-coupled ...chemokine receptors to lyse human erythrocytes (red blood cells) and leukocytes (white blood cells). The first recognition step of receptors is critical for specific cell targeting and lysis. The structural and molecular bases for this mechanism are not well understood but could constitute essential information to guide antibiotic development. Here, we characterized the interaction of LukE with chemokine receptors ACKR1, CCR2, and CCR5 using a combination of structural, pharmacological, and computational approaches. First, crystal structures of LukE in complex with a small molecule mimicking sulfotyrosine side chain (p-cresyl sulfate) and with peptides containing sulfotyrosines issued from receptor sequences revealed the location of receptor sulfotyrosine binding sites in the toxins. Then, by combining previous and novel experimental data with protein docking, classical and accelerated weight histogram (AWH) molecular dynamics we propose models of the ACKR1-LukE and CCR5-LukE complexes. This work provides novel insights into chemokine receptor recognition by leukotoxins and suggests that the conserved sulfotyrosine binding pocket could be a target of choice for future drug development.
Circular dichroism (CD) spectroscopy in the visible region (vis‐CD) is a powerful technique to study metal–protein interactions. It can resolve individual d–d electronic transitions as separate bands ...and is particularly sensitive to the chiral environment of the transition metals. Modern quantum chemical methods enable CD spectra calculations from which, along with direct comparison with the experimental CD data, the conformations and the stereochemistry of the metal–protein complexes can be assigned. However, a clear understanding of the observed spectra and the molecular configuration is largely lacking. In this study, we compare the experimental and computed vis‐CD spectra of Cu2+‐loaded model peptides in square‐planar complexes. We find that the spectra can readily discriminate the coordination pattern of Cu2+ bound exclusively to main‐chain amides from that involving both main‐chain amides and a side‐chain (i.e. histidine side‐chain). Based on the results, we develop a set of empirical rules that relates the appearance of particular vis‐CD spectral features to the conformation of the complex. These rules can be used to gain insight into coordination geometries of other Cu2+–or Ni2+–protein complexes.
Circular dichroism spectroscopy in the visible region (vis‐CD) is a powerful technique to study metal‐protein interactions. Here, we compare experimental and computed vis‐CD spectra for groups of Cu2+ and Ni2+ loaded model peptides, in square‐planar complexes. From this we develop a set of predictive empirical rules that relates the vis‐CD spectral features to coordination geometries of Cu2+ or Ni2+‐protein complexes.
G protein-coupled receptors (GPCRs) conserve common structural folds and activation mechanisms, yet their ligand spectra and functions are highly diverse. This work investigated how the amino-acid ...sequences of olfactory receptors (ORs)the largest GPCR familyencode diversified responses to various ligands. We established a proteochemometric (PCM) model based on OR sequence similarities and ligand physicochemical features to predict OR responses to odorants using supervised machine learning. The PCM model was constructed with the aid of site-directed mutagenesis, in vitro functional assays, and molecular simulations. We found that the ligand selectivity of the ORs is mostly encoded in the residues up to 8 Å around the orthosteric pocket. Subsequent predictions using Random Forest (RF) showed a hit rate of up to 58%, as assessed by in vitro functional assays of 111 ORs and 7 odorants of distinct scaffolds. Sixty-four new OR–odorant pairs were discovered, and 25 ORs were deorphanized here. The best model demonstrated a 56% deorphanization rate. The PCM-RF approach will accelerate OR–odorant mapping and OR deorphanization.
Atomistic descriptions of the μ-opioid receptor (μOR) noncovalently binding with two of its prototypical morphinan agonists, morphine (MOP) and hydromorphone (HMP), are investigated using molecular ...dynamics (MD) simulations. Subtle differences between the binding modes and hydration properties of MOP and HMP emerge from the calculations. Alchemical free energy perturbation calculations show qualitative agreement with in vitro experiments performed in this work: indeed, the binding free energy difference between MOP and HMP computed by forward and backward alchemical transformation is 1.2±1.1 and 0.8±0.8 kcal/mol, respectively, to be compared with 0.4±0.3 kcal/mol from experiment. Comparison with an MD simulation of μOR covalently bound with the antagonist β-funaltrexamine hints to agonist-induced conformational changes associated with an early event of the receptor's activation: a shift of the transmembrane helix 6 relative to the transmembrane helix 3 and a consequent loss of the key R165-T279 interhelical hydrogen bond. This finding is consistent with a previous proposal suggesting that the R165-T279 hydrogen bond between these two helices indicates an inactive receptor conformation.
Membrane proteins are central to many pathophysiological processes, yet remain very difficult to analyze structurally. Moreover, high-throughput structure-based drug discovery has not yet been ...exploited for membrane proteins because of lack of automation. Here, we present a facile and versatile platform for in meso membrane protein crystallization, enabling rapid atomic structure determination at both cryogenic and room temperatures. We apply this approach to human integral membrane proteins, which allowed us to identify different conformational states of intramembrane enzyme-product complexes and analyze by molecular dynamics simulations the structural dynamics of the ADIPOR2 integral membrane protein. Finally, we demonstrate an automated pipeline combining high-throughput microcrystal soaking, automated laser-based harvesting, and serial crystallography, enabling screening of small-molecule libraries with membrane protein crystals grown in meso. This approach brings needed automation to this important class of drug targets and enables high-throughput structure-based ligand discovery with membrane proteins.
Display omitted
•A platform for rapid in meso structures by serial crystallography (SSX)•Insights into ADIPOR2 receptor-ligand dynamic interactions•A web-based application for remote user-guided experimental design and execution•An automated SSX-based ligand discovery pipeline for membrane proteins is introduced
Membrane proteins are key regulators of most physiological processes and represent attractive targets for drug discovery programs. One of the most successful methods to obtain high-resolution structures of membrane proteins relies on in meso crystallization in combination with serial synchrotron crystallography. However, this remains a difficult process, with challenges at every step, including complex manual sample recovery protocols leading to limited throughput and sample loss and the difficulty in carrying out high-throughput ligand screening experiments. We have developed a new approach enabling rapid, automated structural analysis of membrane proteins in meso based on the CrystalDirect technology that addresses these issues, enabling high-throughput drug discovery with membrane proteins.
Membrane proteins control many biological processes and represent attractive targets for drug discovery, but are difficult to study structurally. Healey et al. present an automated approach, combining the CrystalDirect technology and serial crystallography, for rapid structural analysis of membrane proteins and opening new opportunities for high-throughput drug discovery.
G protein-coupled receptors (GPCRs) control most cellular communications with the environment and are the largest protein family of drug targets. As strictly regulated molecular machines, profound ...comprehension of their activation mechanism is expected to significantly facilitate structure-based drug design. This study provides atomistic-level description of the activation dynamics of the C-X-C chemokine receptor type 4 (CXCR4), a class A GPCR and important drug target. Using molecular dynamics and enhanced sampling, we demonstrate how mutations and protonation of conserved residues trigger activation through microswitches at the receptor core, while sodium ion - a known allosteric modulator - inhibits it. The findings point to a conserved mechanism of activation and the allosteric modulation by sodium in the chemokine receptor family. From the technical aspect, the enhanced sampling protocol effectively samples receptor conformational changes toward activation, and differentiates three variants of the receptor by their basal activity. This work provides structural basis and a powerful in silico tool for CXCR4 agonist design.
PDF
