Structural basis of α1A-adrenergic receptor activation and recognition by an extracellular nanobody.

The α1A-adrenergic receptor (α1AAR) belongs to the family of G protein-coupled receptors that respond to adrenaline and noradrenaline. α1AAR is involved in smooth muscle contraction and cognitive function. Here, we present three cryo-electron microscopy structures of human α1AAR bound to the endogenous agonist noradrenaline, its selective agonist oxymetazoline, and the antagonist tamsulosin, with resolutions range from 2.9 Å to 3.5 Å. Our active and inactive α1AAR structures reveal the activation mechanism and distinct ligand binding modes for noradrenaline compared with other adrenergic receptor subtypes. In addition, we identified a nanobody that preferentially binds to the extracellular vestibule of α1AAR when bound to the selective agonist oxymetazoline. These results should facilitate the design of more selective therapeutic drugs targeting both orthosteric and allosteric sites in this receptor family.

Ligand binding to human prostaglandin E receptor EP4 at the lipid-bilayer interface.

Prostaglandin E receptor EP4, a G-protein-coupled receptor, is involved in disorders such as cancer and autoimmune disease. Here, we report the crystal structure of human EP4 in complex with its antagonist ONO-AE3-208 and an inhibitory antibody at 3.2 Å resolution. The structure reveals that the extracellular surface is occluded by the extracellular loops and that the antagonist lies at the interface with the lipid bilayer, proximal to the highly conserved Arg316 residue in the seventh transmembrane domain. Functional and docking studies demonstrate that the natural agonist PGE2 binds in a similar manner. This structural information also provides insight into the ligand entry pathway from the membrane bilayer to the EP4 binding pocket. Furthermore, the structure reveals that the antibody allosterically affects the ligand binding of EP4. These results should facilitate the design of new therapeutic drugs targeting both orthosteric and allosteric sites in this receptor family.

Hot-Spot Residues to be Mutated Common in G Protein-Coupled Receptors of Class A: Identification of Thermostabilizing Mutations Followed by Determination of Three-Dimensional Structures for Two Example Receptors.

G protein-coupled receptors (GPCRs), which are indispensable to life and also implicated in a number of diseases, construct important drug targets. For the efficient structure-guided drug design, however, their structural stabilities must be enhanced. An amino-acid mutation is known to possibly lead to the enhancement, but currently available experimental and theoretical methods for identifying stabilizing mutations suffer such drawbacks as the incapability of exploring the whole mutational space with minor effort and the unambiguous physical origin of the enhanced or lowered stability. In general, after the identification is successfully made for a GPCR, the whole procedure must be followed all over again for the identification for another GPCR. Here we report a theoretical strategy by which many different GPCRs can be considered at the same time. The strategy is illustrated for three GPCRs of Class A in the inactive state. We argue that a mutation of the residue at a position of NBW = 3.39 (NBW is the Ballesteros-Weinstein number), a hot-spot residue, leads to substantially higher stability for significantly many GPCRs of Class A in the inactive state. The most stabilizing mutations of the residues with NBW = 3.39 are then identified for two of the three GPCRs, using the improved version of our free-energy function. These identifications are experimentally corroborated, which is followed by the determination of new three-dimensional (3D) structures for the two GPCRs. We expect that on the basis of the strategy, the 3D structures of many GPCRs of Class A can be solved for the first time in succession.

EphA4-dependent axon retraction and midline localization of Ephrin-B3 are disrupted in the spinal cord of mice lacking mDia1 and mDia3 in combination.

mDia is an actin nucleator and polymerization factor regulated by the small GTPase Rho and consists of three isoforms. Here, we found that mice lacking mDia1 and mDia3, two isoforms expressed in the brain, in combination (mDia-DKO mice) show impaired left-right limb coordination during locomotion and aberrant midline crossing of axons of corticospinal neurons and spinal cord interneurons. Given that mice lacking Ephrin-B3-EphA4 signaling show a similar impairment in locomotion, we examined whether mDia is involved in Ephrin-B3-EphA4 signaling for axon repulsion. In primary cultured neurons, mDia deficiency impairs growth cone collapse and axon retraction induced by chemo-repellants including EphA ligands. In mDia-DKO mice, the Ephrin-B3-expressing midline structure in the spinal cord is disrupted, and axons aberrantly cross the spinal cord midline preferentially through the region devoid of Ephrin-B3. Therefore, mDia plays multiple roles in the proper formation of the neural network in vivo.

The Staudinger reaction with 2-imino-1,3-thiaselenanes toward the synthesis of C4 spiro-ß-lactams.

The Staudinger ketene-imine [2 + 2] cycloaddition reaction for conversion of α-heteroatom-substituted exocyclic imines to C4 heterocyclic spiro-ß-lactams has rarely been investigated due to their instability. Herein, we describe the Staudinger reaction between ketenes and α-selenium-substituted exocyclic imines to synthesize C4 spiro-ß-lactams.

Asymmetric dearomatizing spirolactonization of naphthols catalyzed by spirobiindane-based chiral hypervalent iodine species.

This report details the development of a spirobiindane-based chiral hypervalent iodine reagent, especially focusing on its structural elucidation for effective asymmetric induction of the chiral spiro center during the oxidative dearomatizing spirolactonization of naphthols. In this study we synthesized a new series of ortho-functionalized spirobiindane catalysts and demonstrated that the enantioselectivity can be dramatically improved by the presence of the substituents ortho to the iodine atom. The structural elucidation of a spirobiindane-based hypervalent iodine catalyst has led to further improvement in the stereoselective construction of the spiro center during the oxidative dearomatizing spirolactonization of naphthols. Thus, catalytic oxidation with the highest reported level of enantioselectivity in hypervalent iodine chemistry has been achieved with also an excellent level of asymmetric induction (92% ee for substrate 3a). As a result, this study, dealing with a series of modified iodine catalysts, can provide important clues about the transition state and reaction intermediate to help scientists understand the origin of the stereoselectivity. A plausible transition-state model and intermediate in the reaction for the stereoselective formation of spirolactone products are postulated by considering the ortho-substituent effect and the results of X-ray analysis. In this reaction model, the high enantiomeric excess obtained by using the spirobiindane catalysts could be well explained by the occupation of the equatorial site and extension of the surroundings around the hypervalent iodine bonds by the introduced ortho-substituent. Thus, this study would contribute to estimation of the chiral hypervalent iodine compounds in asymmetric reactions.

Synthesis of boron-substituted diaryliodonium salts and selective transformation into functionalized aryl boronates.

Dormant boron awaits its true destiny in diaryliodonium salts synthesized from aryl boronate derivatives according to two alternative general methods with hypervalent iodine(III) reagents and fluoroalcohol solvents: transformation of an aryl C-H bond and boron-iodine(III) exchange (see scheme; FG = functional group). The salts could be functionalized by both catalyst-free and metal-catalyzed reactions without loss of the boron functionality.

Deficiency of mDia, an actin nucleator, disrupts integrity of neuroepithelium and causes periventricular dysplasia.

During development of the central nervous system, the apical-basal polarity of neuroepithelial cells is critical for homeostasis of proliferation and differentiation of neural stem cells. While adherens junctions at the apical surface of neuroepithelial cells are important for maintaining the polarity, the molecular mechanism regulating integrity of these adherens junctions remains largely unknown. Given the importance of actin cytoskeleton in adherens junctions, we have analyzed the role of mDia, an actin nucleator and a Rho effector, in the integrity of the apical adherens junction. Here we show that mDia1 and mDia3 are expressed in the developing brain, and that mDia3 is concentrated in the apical surface of neuroepithelium. Mice deficient in both mDia1 and mDia3 develop periventricular dysplastic mass widespread throughout the developing brain, where neuroepithelial cell polarity is impaired with attenuated apical actin belts and loss of apical adherens junctions. In addition, electron microscopic analysis revealed abnormal shrinkage and apical membrane bulging of neuroepithelial cells in the remaining areas. Furthermore, perturbation of Rho, but not that of ROCK, causes loss of the apical actin belt and adherens junctions similarly to mDia-deficient mice. These results suggest that actin cytoskeleton regulated by Rho-mDia pathway is critical for the integrity of the adherens junctions and the polarity of neuroepithelial cells, and that loss of this signaling induces aberrant, ectopic proliferation and differentiation of neural stem cells.