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Long-wavelength pulses from the Swiss X-ray free-electron laser (XFEL) have been used for de novo protein structure determination by native single-wavelength anomalous diffraction (native-SAD) phasing of serial femtosecond crystallography (SFX) data. In this work, sensitive anomalous data-quality indicators and model proteins were used to quantify improvements in native-SAD at XFELs such as utilization of longer wavelengths, careful experimental geometry optimization, and better post-refinement and partiality correction. Compared with studies using shorter wavelengths at other XFELs and older software versions, up to one order of magnitude reduction in the required number of indexed images for native-SAD was achieved, hence lowering sample consumption and beam-time requirements significantly. Improved data quality and higher anomalous signal facilitate so-far underutilized de novo structure determination of challenging proteins at XFELs. Improvements presented in this work can be used in other types of SFX experiments that require accurate measurements of weak signals, for example time-resolved studies., IUCrJ, 7 (6), ISSN:2052-2525

The in meso in situ serial X-ray crystallization method (Huang et al., (2015) Acta Crystallogr D Biol Crystallogr 71, 1238) combines lipid cubic phase crystallization, direct freezing of the crystallization droplet without handling of the crystals, and data collection in situ. Recently, this method was used to overcome the mechanical fragility of crystals which enabled the X-ray structure determination of chemokine receptor 2A (Apel et al., (2019) Structure 27, 427) at 2.7 Å resolution. The CCR2 structure provides the structural basis for ligand selectivity of CCR2 against chemokine receptor 5 and provides insights into the residence time of MK-0812 analogs based on molecular dynamics simulations. These findings offer new opportunities for drug discovery targeting chemokine receptors.

Kv3 ion-channels constitute a class of functionally distinct voltage gated ion channels characterized by their ability to fire at a high frequency. Several disease relevant mutants, together with biological data, suggest the importance of this class of ion channels as drug targets for CNS disorders, and several drug discovery efforts have been reported. Despite the increasing interest for this class of ion channels, no structure of a Kv3 channel has been reported yet. We have determined the cryo-EM structure of Kv3.1 at 2.6 Å resolution using full length wild type protein. When compared to known structures for potassium channels from other classes, a novel domain organization is observed with the cytoplasmic T1 domain, containing a well resolved Zinc site and displaying a rotation by 35°. This suggests a distinct cytoplasmic regulation mechanism for the Kv3.1 channel. A high resolution structure was obtained for Kv3.1 in complex with a novel positive modulator Lu AG00563. The structure reveals a novel ligand binding site for the Kv class of ion channels located between the voltage sensory domain and the channel pore, a region which constitutes a hotspot for disease causing mutations. The discovery of a novel binding site for a positive modulator of a voltage gated potassium channel could shed light on the mechanism of action for these small molecule potentiators. This finding could enable structure-based drug design on these targets with high therapeutic potential for the treatment of multiple CNS disorders.

In this study, we determined the crystal structure of an engineered human adenosine A2A receptor bound to a partial agonist and compared it to structures cocrystallized with either a full agonist or an antagonist/inverse agonist. The interaction between the partial agonist, belonging to a class of dicyanopyridines, and amino acids in the ligand binding pocket inspired us to develop a small library of derivatives and assess their affinity in radioligand binding studies and potency and intrinsic activity in a functional, label-free, intact cell assay. It appeared that some of the derivatives retained the partial agonist profile, whereas other ligands turned into inverse agonists. We rationalized this remarkable behavior with additional computational docking studies.

In this study, we determined the crystal structure of an engineered human adenosine A2A receptor bound to a partial agonist and compared it to structures cocrystallized with either a full agonist or an antagonist/inverse agonist. The interaction between the partial agonist, belonging to a class of dicyanopyridines, and amino acids in the ligand binding pocket inspired us to develop a small library of derivatives and assess their affinity in radioligand binding studies and potency and intrinsic activity in a functional, label-free, intact cell assay. It appeared that some of the derivatives retained the partial agonist profile, whereas other ligands turned into inverse agonists. We rationalized this remarkable behavior with additional computational docking studies.

Lipopolysaccharides (LPS) are major constituents of the extracellular leaflet in the bacterial outer membrane and form an effective physical barrier for environmental threats and for antibiotics in Gram-negative bacteria 1. The last step of LPS insertion via the Lpt pathway is mediated by the LptD/E protein complex 2. Despite detailed insights from X-ray crystallography into the architecture of LptDE transporter complexes 3–5, no structure of a laterally open LptD transporter has been described, a transient state that occurs during LPS release 6. To facilitate the acquisition of hitherto unknown conformations we subjected LptDE of N. gonorrhoeae to cryo-EM analyses. In complex with newly designed rigid chaperones derived from nanobodies (Pro-Macrobodies, PMbs) we obtained a map of a partially opened LptDE transporter at 3.4 Å resolution and in addition we captured a laterally fully opened LptDE complex from a subset of particles. Our work offers new insights into the mechanism of LPS insertion, provides a structural framework for the development of antibiotics targeting LptD and describes a novel, highly rigid and widely applicable chaperone scaffold to enable structural biology of challenging protein targets.

Crystal structures of protease-activated receptor 2 (PAR2) in complex with two different antagonist ligands and with a blocking antibody reveal binding sites that are distinct from those found on PAR1, offering new leads for structure-based drug design. Protease-activated receptors (PARs) are a family of G-protein-coupled receptors (GPCRs) with roles in diverse diseases, such as neuroinflammation and cancer, and are considered important target for drug discovery. Here, Fiona Marshall and colleagues have determined three crystal structures of PAR2 in complex with two different antagonists and a blocking antibody, respectively. The antagonists bind to distinct allosteric sites on the receptor and these binding sites are different to the one previously found on PAR1. Therefore this family of GPCRs can be inhibited by a number of different allosteric mechanisms, offering new leads for structure-based drug design. Protease-activated receptors (PARs) are a family of G-protein-coupled receptors (GPCRs) that are irreversibly activated by proteolytic cleavage of the N terminus, which unmasks a tethered peptide ligand that binds and activates the transmembrane receptor domain, eliciting a cellular cascade in response to inflammatory signals and other stimuli. PARs are implicated in a wide range of diseases, such as cancer and inflammation1,2,3. PARs have been the subject of major pharmaceutical research efforts3 but the discovery of small-molecule antagonists that effectively bind them has proved challenging. The only marketed drug targeting a PAR is vorapaxar4, a selective antagonist of PAR1 used to prevent thrombosis. The structure of PAR1 in complex with vorapaxar has been reported previously5. Despite sequence homology across the PAR isoforms, discovery of PAR2 antagonists has been less successful, although GB88 has been described as a weak antagonist6. Here we report crystal structures of PAR2 in complex with two distinct antagonists and a blocking antibody. The antagonist AZ8838 binds in a fully occluded pocket near the extracellular surface. Functional and binding studies reveal that AZ8838 exhibits slow binding kinetics, which is an attractive feature for a PAR2 antagonist competing against a tethered ligand. Antagonist AZ3451 binds to a remote allosteric site outside the helical bundle. We propose that antagonist binding prevents structural rearrangements required for receptor activation and signalling. We also show that a blocking antibody antigen-binding fragment binds to the extracellular surface of PAR2, preventing access of the tethered ligand to the peptide-binding site. These structures provide a basis for the development of selective PAR2 antagonists for a range of therapeutic uses.

Controlling the Dissociation of Ligands from the Adenosine A2A Receptor through Modulation of Salt Bridge StrengthElena Segala, Dong Guo, Robert K. Y. Cheng, Andrea Bortolato, Francesca Deflorian, Andrew S. Doré, James C. Errey, Laura H. Heitman, Adriaan P. IJzerman, Fiona H. Marshall, and Robert M. CookeHeptares Therapeutics Ltd, Biopark Broadwater Road, Welwyn Garden City AL7 3AX, U.K.Division of Medicinal Chemistry, Leiden Academic Centre for Drug Research (LACDR), Leiden University P.O. Box 9502, 2300 RA Leiden, the NetherlandsAbstractThe association and dissociation kinetics of ligands binding to proteins vary considerably, but the mechanisms behind this variability are poorly understood, limiting their utilization for drug discovery. This is particularly so for G protein-coupled receptors (GPCRs) where high resolution structural information is only beginning to emerge. Engineering the human A2A adenosine receptor has allowed structures to be solved in complex with the reference compound ZM241385 and four related ligands at high resolution. Differences between the structures are limited, with the most pronounced being the interaction of each ligand with a salt bridge on the extracellular side of the receptor. Mutagenesis experiments confirm the role of this salt bridge in controlling the dissociation kinetics of the ligands from the receptor, while molecular dynamics simulations demonstrate the ability of ligands to modulate salt bridge stability. These results shed light on a structural determinant of ligand dissociation kinetics and identify a means by which this property may be optimized.

Accumulation of extracellular adenosine within the microenvironment is a strategy exploited by tumors to escape detection by the immune system. Adenosine signaling through the adenosine 2A receptor (A2AR) on immune cells elicits a range of immunosuppressive effects which promote tumor growth and limit the efficacy of immune checkpoint inhibitors. Preclinical data with A2AR inhibitors have demonstrated tumor regressions in mouse models by rescuing T cell function; however, the mechanism and role on other immune cells has not been fully elucidated.MethodsWe report here the development of a small molecule A2AR inhibitor including characterization of binding and inhibition of A2AR function with varying amounts of a stable version of adenosine. Functional activity was tested in both mouse and human T cells and dendritic cells (DCs) in in vitro assays to understand the intrinsic role on each cell type. The role of adenosine and A2AR inhibition was tested in DC differentiation assays as well as co-culture assays to access the cross-priming function of DCs. Syngeneic models were used to assess tumor growth alone and in combination with alphaprogrammed death-ligand 1 (αPD-L1). Immunophenotyping by flow cytometry was performed to examine global immune cell changes upon A2AR inhibition.ResultsWe provide the first report of AZD4635, a novel small molecule A2AR antagonist which inhibits downstream signaling and increases T cell function as well as a novel mechanism of enhancing antigen presentation by CD103+ DCs. The role of antigen presentation by DCs, particularly CD103+ DCs, is critical to drive antitumor immunity providing rational to combine a priming agent AZD4635 with check point blockade. We find adenosine impairs the maturation and antigen presentation function of CD103+ DCs. We show in multiple syngeneic mouse tumor models that treatment of AZD4635 alone and in combination with αPD-L1 led to decreased tumor volume correlating with enhanced CD103+ function and T cell response. We extend these studies into human DCs to show that adenosine promotes a tolerogenic phenotype that can be reversed with AZD4635 restoring antigen-specific T cell activation. Our results support the novel role of adenosine signaling as an intrinsic negative regulator of CD103+ DCs maturation and priming. We show that potent inhibition of A2AR with AZD4635 reduces tumor burden and enhances antitumor immunity. This unique mechanism of action in CD103+ DCs may contribute to clinical responses as AZD4635 is being evaluated in clinical trials with IMFINZI (durvalumab, αPD-L1) in patients with solid malignancies.ConclusionWe provide evidence implicating suppression of adaptive and innate immunity by adenosine as a mechanism for immune evasion by tumors. Inhibition of adenosine signaling through selective small molecule inhibition of A2AR using AZD4635 restores T cell function via an internal mechanism as well as tumor antigen cross-presentation by CD103+ DCs resulting in antitumor immunity.

Here we report an efficient method to generate multiple co-structures of the A2A G protein-coupled receptor (GPCR) with small-molecules from a single preparation of a thermostabilised receptor crystallised in Lipidic Cubic Phase (LCP). Receptor crystallisation is achieved following purification using a low affinity “carrier” ligand (theophylline) and crystals are then soaked in solutions containing the desired (higher affinity) compounds. Complete datasets to high resolution can then be collected from single crystals and seven structures are reported here of which three are novel. The method significantly improves structural throughput for ligand screening using stabilised GPCRs, thereby actively driving Structure-Based Drug Discovery (SBDD).

Here we report an efficient method to generate multiple co-structures of the A2A G protein-coupled receptor (GPCR) with small-molecules from a single preparation of a thermostabilised receptor crystallised in Lipidic Cubic Phase (LCP). Receptor crystallisation is achieved following purification using a low affinity “carrier” ligand (theophylline) and crystals are then soaked in solutions containing the desired (higher affinity) compounds. Complete datasets to high resolution can then be collected from single crystals and seven structures are reported here of which three are novel. The method significantly improves structural throughput for ligand screening using stabilised GPCRs, thereby actively driving Structure-Based Drug Discovery (SBDD).

The structural analysis of class B G protein-coupled receptors (GPCR), cell surface proteins responding to peptide hormones, has until recently been restricted to the extracellular domain (ECD). Cor-ticotropin-releasing factor receptor type 1 (CRF1R) is a class B receptor mediating stress response and also considered a drug target for depression and anxiety. Here we report the crystal structure of the trans-membrane domain of human CRF1R in complex with the small-molecule antagonist CP-376395 in a hex-agonal setting with translational non-crystallographic symmetry. Molecular dynamics and metadynamics simulations on this novel structure and the existing TMD structure for CRF1R provides insight as to how the small molecule ligand gains access to the induced-fit allosteric binding site with implications for the observed selectivity against CRF2R. Furthermore, molecular dynamics simulations performed using a full-length receptor model point to key interactions between the ECD and extracellular loop 3 of the TMD providing insight into the full inactive state of multidomain class B GPCRs.

Historically, room-temperature structure determination was succeeded by cryo-crystallography to mitigate radiation damage. Here, we demonstrate that serial millisecond crystallography at a synchrotron beamline equipped with high-viscosity injector and high frame-rate detector allows typical crystallographic experiments to be performed at room-temperature. Using a crystal scanning approach, we determine the high-resolution structure of the radiation sensitive molybdenum storage protein, demonstrate soaking of the drug colchicine into tubulin and native sulfur phasing of the human G protein-coupled adenosine receptor. Serial crystallographic data for molecular replacement already converges in 1,000–10,000 diffraction patterns, which we collected in 3 to maximally 82 minutes. Compared with serial data we collected at a free-electron laser, the synchrotron data are of slightly lower resolution, however fewer diffraction patterns are needed for de novo phasing. Overall, the data we collected by room-temperature serial crystallography are of comparable quality to cryo-crystallographic data and can be routinely collected at synchrotrons., Nature Communications, 8, ISSN:2041-1723

Past decades have shown the impact of structural information derived from complexes of drug candidates with their protein targets to facilitate the discovery of safe and effective medicines. Despite recent developments in single particle cryo-electron microscopy, X-ray crystallography has been the main method to derive structural information. The unique properties of X-ray free electron laser (XFEL) with unmet peak brilliance and beam focus allow X-ray diffraction data recording and successful structure determination from smaller and weaker diffracting crystals shortening timelines in crystal optimization. To further capitalize on the XFEL advantage, innovations in crystal sample delivery for the X-ray experiment, data collection and processing methods are required. This development was a key contributor to serial crystallography allowing structure determination at room temperature yielding physiologically more relevant structures. Adding the time resolution provided by the femtosecond X-ray pulse will enable monitoring and capturing of dynamic processes of ligand binding and associated conformational changes with great impact to the design of candidate drug compounds.

Structural analysis of class B G-protein-coupled receptors (GPCRs), cell-surface proteins that respond to peptide hormones, has been restricted to the amino-terminal extracellular domain, thus providing little understanding of the membrane-spanning signal transduction domain. The corticotropin-releasing factor receptor type 1 is a class B receptor which mediates the response to stress and has been considered a drug target for depression and anxiety. Here we report the crystal structure of the transmembrane domain of the human corticotropin-releasing factor receptor type 1 in complex with the small-molecule antagonist CP-376395. The structure provides detailed insight into the architecture of class B receptors. Atomic details of the interactions of the receptor with the non-peptide ligand that binds deep within the receptor are described. This structure provides a model for all class B GPCRs and may aid in the design of new small-molecule drugs for diseases of brain and metabolism.

The emergence and spread of multidrug-resistant (MDR) Gram negative bacteria presents a serious threat for public health. Novel antimicrobials that could overcome the resistance problems are urgently needed. UDP-3-O-(R-3-hydroxymyristol)-N-acetylglucosamine deacetylase (LpxC) is a cytosolic zinc-based deacetylase that catalyzes the first committed step in the biosynthesis of lipid A, which is essential for the survival of Gram-negative bacteria. Our efforts toward the discovery of novel LpxC inhibitors are presented herein.

The adenosine A

Tissue transglutaminase 2 (TG2) is a multifunctional protein primarily known for its calcium-dependent enzymatic protein cross-linking activity via isopeptide bond formation between glutamine and lysine residues. TG2 overexpression and activity have been found to be associated with Huntington's disease (HD); specifically, TG2 is up-regulated in the brains of HD patients and in animal models of the disease. Interestingly, genetic deletion of TG2 in two different HD mouse models, R6/1 and R6/2, results in improved phenotypes including a reduction in neuronal death and prolonged survival. Starting with phenylacrylamide screening hit 7d, we describe the SAR of this series leading to potent and selective TG2 inhibitors. The suitability of the compounds as in vitro tools to elucidate the biology of TG2 was demonstrated through mode of inhibition studies, characterization of druglike properties, and inhibition profiles in a cell lysate assay.

(1,1-Dioxo-2H-[1,2,4]benzothiadiazin-3-yl) azolo[1,5-a]pyridine and azolo[1,5-a]pyrimidine derivatives have been investigated as potential anti-HCV drugs. Their synthesis, HCV NS5B polymerase inhibition, and replicon activity are discussed.

Heat shock protein 90 (Hsp90) plays a key role in stress response and protection of the cell against the effects of mutation. Herein we report the identification of an Hsp90 inhibitor identified by fragment screening using a high-concentration biochemical assay, as well as its optimisation by in silico searching coupled with a structure-based drug design (SBDD) approach.

Inhibitors of the ATPase function of bacterial DNA gyrase, located in the GyrB subunit and its related ParE subunit in topoisomerase IV, have demonstrated antibacterial activity. In this study we describe an NMR fragment-based screening effort targeting Staphylococcus aureus GyrB that identified several attractive and novel starting points with good ligand efficiency. Fragment hits were further characterized using NMR binding studies against full-length S. aureus GyrB and Escherichia coli ParE. X-ray co-crystal structures of select fragment hits confirmed binding and suggested a path for medicinal chemistry optimization. The identification, characterization, and elaboration of one of these fragment series to a 0.265 μM inhibitor is described herein.

The Mapkap kinases 2 and 3 (MK2 and MK3) have been implicated in intracellular signaling pathways leading to the production of the pro-inflammatory cytokine tumor necrosis factor alpha. MK2 has been pursued by the biopharmaceutical industry for many years for the development of a small molecule anti-inflammatory treatment and drug-like inhibitors have been described. The development of some of these compounds, however, has been slowed by the absence of a high-resolution crystal structure of MK2. Herein we present a high-resolution (1.9 A) crystal structure of the highly homologous MK3 in complex with a pharmaceutical lead compound. While all of the canonical features of Ser/Thr kinases in general and MK2 in particular are recapitulated in MK3, the detailed analysis of the binding interaction of the drug-like ligand within the adenine binding pocket allows relevant conclusions to be drawn for the further design of potent and selective drug candidates.