Biomedical subjects

Hiroyasu Furukawa

Publications and source records attributed to Hiroyasu Furukawa.

7 recordsLinked to original sources

PubMed2007

Hypoxia enhances S-nitrosylation-mediated NMDA receptor inhibition via a thiol oxygen sensor motif.

Under ambient air conditions, NO inhibits NMDAR activity by reacting with the NR2A subunit C399 along with two additional cysteine pairs if their disulfide bonds are reduced to free thiol groups [NR1(C744,C798); NR2(C87,C320)]. Here we demonstrate that relative hypoxia enhances S-nitrosylation of NMDARs by a unique mechanism involving an "NO-reactive oxygen sensor motif" whose determinants include C744 and C798 of the NR1 subunit. Redox reactions involving these two thiol groups sensitize other NMDAR sites to S-nitrosylation and consequent receptor inhibition, while their own nitrosylation has little effect on NMDAR activity. The crystal structure of the ligand-binding domain of NR1 reveals a flexible disulfide bond (C744-C798), which may account for its susceptibility to reduction and subsequent reaction with NO that is observed with biochemical techniques. These thiols may be nitrosylated preferentially during increasing hypoxia or stroke conditions, thus preventing excessive activity associated with cytotoxicity while avoiding blockade of physiologically active NMDARs.

Amino Acid Motifs↗

PubMed2006

Crystal structure, dissolution, and deposition of a 5 nm functionalized metal-organic great rhombicuboctahedron.

A metal-organic great rhombicuboctahedron (termed MOP-18) was functionalized with extended alkyl chains and crystallized. It has 12 rigid square-shaped Cu2(CO2)4 paddle-wheel building units and 24 5-dodecoxybenzene-1,3-dicarboxylate links. MOP-18 is soluble in a variety of organic solvents, such as tetrahydrofuran, chloroform, and toluene, which enabled its assembly on graphite substrate and its observation by scanning tunneling microscopy.

Crystallography, X-Ray↗

PubMed2005

Subunit arrangement and function in NMDA receptors.

Excitatory neurotransmission mediated by NMDA (N-methyl-D-aspartate) receptors is fundamental to the physiology of the mammalian central nervous system. These receptors are heteromeric ion channels that for activation require binding of glycine and glutamate to the NR1 and NR2 subunits, respectively. NMDA receptor function is characterized by slow channel opening and deactivation, and the resulting influx of cations initiates signal transduction cascades that are crucial to higher functions including learning and memory. Here we report crystal structures of the ligand-binding core of NR2A with glutamate and that of the NR1-NR2A heterodimer with glutamate and glycine. The NR2A-glutamate complex defines the determinants of glutamate and NMDA recognition, and the NR1-NR2A heterodimer suggests a mechanism for ligand-induced ion channel opening. Analysis of the heterodimer interface, together with biochemical and electrophysiological experiments, confirms that the NR1-NR2A heterodimer is the functional unit in tetrameric NMDA receptors and that tyrosine 535 of NR1, located in the subunit interface, modulates the rate of ion channel deactivation.

Animals↗

PubMed2005

Mechanism of partial agonist action at the NR1 subunit of NMDA receptors.

Partial agonists produce submaximal activation of ligand-gated ion channels. To address the question of partial agonist action at the NR1 subunit of the NMDA receptor, we performed crystallographic and electrophysiological studies with 1-aminocyclopropane-1-carboxylic acid (ACPC), 1-aminocyclobutane-1-carboxylic acid (ACBC), and 1-aminocyclopentane-1-carboxylic acid (cycloleucine), three compounds with incrementally larger carbocyclic rings. Whereas ACPC and ACBC partially activate the NMDA receptor by 80% and 42%, respectively, their cocrystal structures of the NR1 ligand binding core show the same degree of domain closure as found in the complex with glycine, a full agonist, illustrating that the NR1 subunit provides a new paradigm for partial agonist action that is distinct from that of the evolutionarily related GluR2, AMPA-sensitive receptor. Cycloleucine behaves as an antagonist and stabilizes an open-cleft conformation. The NR1-cycloleucine complex forms a dimer that is similar to the GluR2 dimer, thereby suggesting a conserved mode of subunit-subunit interaction in AMPA and NMDA receptors.

Amino Acids, Cyclic↗

PubMed2005

Energy transfer between chlorophyll derivatives in silica mesostructured films and photocurrent generation.

Layered silica/surfactant mesostructured thin films containing chlorophyllous pigments [C13(2)-demethoxycarbonyl-pheophytin b (pyroPheo b) or zinc C13(2)-demethoxycarbonyl-chlorophyll b (Zn-pyroChl b)] have been prepared on an indium tin oxide (ITO) electrode grafted with a chlorophyll derivative possessing a triethoxysilyl group (copper C13(2)-demethoxycarbonyl-chlorophyllide a 3-triethoxysilyl propylamide, Cu-APTES-Chl a) to achieve effective light harvesting and successive photocurrent generation by the mesostructured films. The incorporation of pyroPheo b and Zn-pyroChl b in the mesostructured film resulted in 1.2- and 1.6-fold increases of the photocurrent density, respectively, as compared to the case of an antenna pigment-free film also grafted to a surface-modified ITO electrode. The difference action spectra, between the electrodes with and without the antenna pigments, coincided well with the absorption spectra of the immobilized pigments. Because direct electron injection from the antenna pigments in the mesostructured films to the ITO electrode was scarcely observed, the energy transfer from the antenna pigments to Cu-APTES-Chl a plays an important role for the increase in photocurrent density. The usefulness of the mesostructured films as model systems is discussed in relation to the photosynthetic primary processes of higher plants.

Journal Article↗

PubMed2003

Mechanisms of activation, inhibition and specificity: crystal structures of the NMDA receptor NR1 ligand-binding core.

Excitatory neurotransmission mediated by the N-methyl-D-aspartate subtype of ionotropic glutamate receptors is fundamental to the development and function of the mammalian central nervous system. NMDA receptors require both glycine and glutamate for activation with NR1 and NR2 forming glycine and glutamate sites, respectively. Mechanisms to describe agonist and antagonist binding, and activation and desensitization of NMDA receptors have been hampered by the lack of high-resolution structures. Here, we describe the cocrystal structures of the NR1 S1S2 ligand-binding core with the agonists glycine and D-serine (DS), the partial agonist D-cycloserine (DCS) and the antagonist 5,7-dichlorokynurenic acid (DCKA). The cleft of the S1S2 'clamshell' is open in the presence of the antagonist DCKA and closed in the glycine, DS and DCS complexes. In addition, the NR1 S1S2 structure reveals the fold and interactions of loop 1, a cysteine-rich region implicated in intersubunit allostery.

Amino Acid Sequence↗

PubMed2002

Conformation of ligands bound to the muscarinic acetylcholine receptor.

Many biogenic amines evoke a variety of physiological responses by acting on G protein-coupled receptors. We have determined the conformation of two acetylcholine analogs, (S)-methacholine and (2S,4R,5S)-muscarine, bound to the M(2) muscarinic acetylcholine receptor (M(2) mAChR) by NMR spectroscopy. The analysis of the transferred nuclear Overhauser effect indicated that the receptor selectively recognized the conformers of (S)-methacholine and (2S,4R,5S)-muscarine with the gauche O-C2-C1-N dihedral angle at +60 degrees. This is distinct from the predominant conformations of these ligands in solution with O-C2-C1-N dihedral angle (+80 to approximately 85 degrees ) in the absence of the M(2) mAChR, as assessed by analyses of the coupling constants and nuclear Overhauser effect spectroscopy. We have also built a molecular model of the M(2) mAChR-(S)-methacholine complex, based on the X-ray crystallographic structure of rhodopsin. This model indicated that the conformation with the gauche O-C2-C1-N dihedral angle at +55.5 degrees, which is similar to the one determined by NMR measurement, is energetically favored in the binding of (S)-methacholine to the receptor. We suggest that this conformation represents the binding of the agonist to the M(2) mAChR in the absence of G protein.

Animals↗