Recognition of phytotropins by the receptor for 1-N-naphthylphthalamic acid

The structure requirements for phytotropin activity and receptor binding are expressed in terms of a recognition site on the receptor with which phytotropins, including 1-N-naphthylphthalamic acid, interact. It is postulated that the site can be represented by a large region which accepts planar molecules, and is possibly electrophilic in nature. A second area is also postulated which may be lipophilic or electrophilic, together with a carboxyl acceptor. It is suggested that if the requirements of the carboxyl acceptor and adjacent area are met, then phytotropin activity will result if the candidate molecule has a configuration, or can adopt a configuration, such that a conjugated portion of the molecule can interact with the larger area. It is argued that the close relationship observed between receptor binding and effect on the gravitropic response implies that the receptors may be directly involved in the gravitropic response mechanism.     

Phytotropins: III. NAPHTHYLPHTHALAMIC ACID BINDING SITES ON MAIZE COLEOPTILE MEMBRANES AS POSSIBLE RECEPTOR SITES FOR PHYTOTROPIN ACTION

Certain members of the phytotropin class of auxin transport inhibitors are shown to bind with high affinity to the known naphthylphthalamic acid binding sites in maize (Zea mays) coleoptiles. The binding site is, thus, a phytotropin binding site. In general, the degree of binding correlates with the phytotropin structure activity rules and with physiological activities of model compounds. It is argued that the binding site may be a receptor, and it also may be the receptor involved in the control of the auxin transport process. The possibility is raised that the binding sites may be intrinsic receptors for endoanalog(s) of the phytotropins.     

Interaction of phytotropins with the NPA receptor

The chemical and stereochemical properties of phytotropins are described in terms of a receptor model, based on their ability to bind to a receptor isolated from maize coleoptiles. Their root gravitropic properties are correlated with their ability to bind to the receptor. It is suggested that their ability to inhibit auxin transport, without more, may not be enough to explain their physiological effects.     

Further studies on the binding of N1-substituted tryptamines at h5-HT6 receptors

N(1)-Arylsulfonyl-substituted analogs of N,N-dimethyltryptamine bind at 5-HT(6) receptors. Replacement of the aryl moiety with similarly hydrophobic alkyl substituents results in decreased affinity, as does replacement of a benzenesulfonyl moiety with a benzyl group. Current findings indicate that an aryl (or substituted aryl) sulfonyl (rather than alkylsulfonyl or benzyl) moiety is optimal for high-affinity binding, and further suggest that the N(1)-benzenesulfonyl- and their corresponding N(1)-benzyltryptamine counterparts bind in a different fashion.     

Inhibitors of the aminoglycoside 6′-N-acetyltransferase type Ib [AAC(6′)-Ib] identified by in silico molecular docking

AAC(6′)-Ib is an important aminoglycoside resistance enzyme to target with enzymatic inhibitors. An in silico screening approach was used to identify potential inhibitors from the ChemBridge library. Several compounds were identified, of which two of them, 4-[(2-{[1-(3-methylphenyl)-4,6-dioxo-2-thioxotetrahydro-5(2H)-pyrimidinylidene]methyl}phenoxy)methyl]benzoic acid and 2-{5-[(4,6-dioxo-1,3-diphenyl-2-thioxotetrahydro-5(2H)-pyrimidinylidene)methyl]-2-furyl}benzoic acid, showed micromolar activity in inhibiting acetylation of kanamycin A. These compounds are predicted to bind the aminoglycoside binding site of AAC(6′)-Ib and exhibited competitive inhibition against kanamycin A.     

Phytotropin-induced root phototropism in maize

Phytotropins, even those not absorbing in the visible region of the spectrum, can induce a phototropic response in maize ( Zea mays L. cv. PX-75) roots when illuminated unilaterally with white light. The most active phytotropin, 2-(1-pyrenoyl) benzoic acid (PBA) can elicit a full response at 10 μ M , while the other active molecules, 2-carboxyphenyl-3-phenylpropane-1,3-dione (CPD), 2-carboxyphenyl-3-phenyl-1,2-pyrazole (CPP), 1-N-naphthylphthalamic acid (NPA) and erythrosin elicit a full response at 100 μ M . The less active phytotropins BBA and fluorescein give a reduced response. It is suggested that the observed effect cannot be explained solely on the basis of auxin transport inhibition. There is a photoreceptor in the extension zone of the root, which may be associated in some way with the receptor for NPA. The results are consistent with the proposal that the phototropic process may form part of the root gravitropic response mechanism.     

Synthesis and hydrolytic evaluation of acid-labile imine-linked cytotoxic isatin model systems

In this study a series of isatin-based, pH-sensitive aryl imine derivatives with differing aromatic substituents and substitution patterns were synthesised and their acid-catalysed hydrolysis evaluated. These derivatives were functionalised at the C3 carbonyl group of a potent N-substituted isatin cytotoxin and were stable at physiological pH but readily cleaved at pH 4.5. Observed rates of hydrolysis for the embedded imine-acid moiety were in the order para-phenylpropionic acid>phenylacetic acid (para>meta)>benzoic acid (meta>para). The ability to fine-tune hydrolysis rates in this way has potential implications for optimising imine linked, tumour targeting cytotoxin-protein conjugates.     

Small molecules can selectively inhibit ephrin binding to the EphA4 and EphA2 receptors

The erythropoietin-producing hepatocellular (Eph) family of receptor tyrosine kinases regulates a multitude of physiological and pathological processes. Despite the numerous possible research and therapeutic applications of agents capable of modulating Eph receptor function, no small molecule inhibitors targeting the extracellular domain of these receptors have been identified. We have performed a high throughput screen to search for small molecules that inhibit ligand binding to the extracellular domain of the EphA4 receptor. This yielded a 2,5-dimethylpyrrolyl benzoic acid derivative able to inhibit the interaction of EphA4 with a peptide ligand as well as the natural ephrin ligands. Evaluation of a series of analogs identified an isomer with similar inhibitory properties and other less potent compounds. The two isomeric compounds act as competitive inhibitors, suggesting that they target the high affinity ligand-binding pocket of EphA4 and inhibit ephrin-A5 binding to EphA4 with K(i) values of 7 and 9 mum in enzyme-linked immunosorbent assays. Interestingly, despite the ability of each ephrin ligand to promiscuously bind many Eph receptors, the two compounds selectively target EphA4 and the closely related EphA2 receptor. The compounds also inhibit ephrin-induced phosphorylation of EphA4 and EphA2 in cells, without affecting cell viability or the phosphorylation of other receptor tyrosine kinases. Furthermore, the compounds inhibit EphA4-mediated growth cone collapse in retinal explants and EphA2-dependent retraction of the cell periphery in prostate cancer cells. These data demonstrate that the Eph receptor-ephrin interface can be targeted by inhibitory small molecules and suggest that the two compounds identified will be useful to discriminate the activities of EphA4 and EphA2 from those of other co-expressed Eph receptors that are activated by the same ephrin ligands. Furthermore, the newly identified inhibitors represent possible leads for the development of therapies to treat pathologies in which EphA4 and EphA2 are involved, including nerve injuries and cancer.     

Ade NovoDesign Probe of a Dopamine Receptor Ligand Based on a Theoretical Approach

A trial to designde novoa dopamine (DA) receptor ligand was made, taking as the base four structural and electrostatic requirements: (1) a group simulating the interaction of the DA amino group with the TM3 aspartic acid of the receptor, (2) a group that can simulate the interaction of the DAm-hydroxyl group with the TM5 serine of the receptor, (3) a distance between these groups similar to that of the DAanti-coplanar conformer, and (4) a rigid structure keeping the distance between the groups right. After the design “on paper” of the models of four structures, quantum chemistry calculations were performed to check the properties of the molecules, and then the most encouraging ones were synthesized. None of the compounds synthesized was able to bind D₁- and D₂-dopamine receptor subtypes; this shows that the structural and electrostatic requirements considered in this work are insufficient. In particular, the presence of an arylethylamine moiety seems to be essential for the interaction of a ligand with the DA receptor.     

In-vitro auxin transport in membrane vesicles from maize coleoptiles

When membrane vesicles from maize (Zea mays L.) coleoptiles are extracted at high buffer strength, a pH-driven, saturable association of [¹⁴C] indole-3-acetic acid is found, similar to the in-vitro auxin-transport system previously described for Cucurbita hypocotyls. The phytotropins naphthylphthalamic acid and pyrenoylbenzoic acid increase net uptake, pressumably by inhibiting the auxin-efflux carrier.Abbreviations IAA indole-3-acetic acid - ION3 ionophore mixture of carbonylcyanide-3-chlorophenylhydrazone, nigericin and valinomycin - 1-NAA, 2-NAA 1-, 2-naphthaleneacetic acid - NPA 1-N-naphthylphthalamic acid - PBA 2-(1-pyrenoyl)benzoic acid     

Amphipathic benzoic acid derivatives: synthesis and binding in the hydrophobic tunnel of the zinc deacetylase LpxC

The first committed step in lipid A biosynthesis is catalyzed by uridine diphosphate-(3-O-(R-3-hydroxymyristoyl))-N-acetylglucosamine deacetylase (LpxC), a zinc-dependent deacetylase, and inhibitors of LpxC may be useful in the development of antibacterial agents targeting a broad spectrum of Gram-negative bacteria. Here, we report the design of amphipathic benzoic acid derivatives that bind in the hydrophobic tunnel in the active site of LpxC. The hydrophobic tunnel accounts for the specificity of LpxC toward substrates and substrate analogues bearing a 3-O-myristoyl substituent. Simple benzoic acid derivatives bearing an aliphatic 'tail' bind in the hydrophobic tunnel with micromolar affinity despite the lack of a glucosamine ring like that of the substrate. However, although these benzoic acid derivatives each contain a negatively charged carboxylate 'warhead' intended to coordinate to the active site zinc ion, the 2.25A resolution X-ray crystal structure of LpxC complexed with 3-(heptyloxy)benzoate reveals 'backward' binding in the hydrophobic tunnel, such that the benzoate moiety does not coordinate to zinc. Instead, it binds at the outer end of the hydrophobic tunnel. Interestingly, these ligands bind with affinities comparable to those measured for more complicated substrate analogue inhibitors containing glucosamine ring analogues and hydroxamate 'warheads' that coordinate to the active site zinc ion. We conclude that the intermolecular interactions in the hydrophobic tunnel dominate enzyme affinity in this series of benzoic acid derivatives.     

The molecular basis of the antidepressant action of the magic mushroom extract,psilocin

Magic mushrooms, and their extract psilocybin, are well-known for their psychedelic properties and recreational use. Psilocin, the bio-active form of psilocybin, can potentially treat various psychiatric diseases. Psilocin putatively exerts its psychedelic effect as an agonist to the serotonin 2A receptor (5-HT_2AR), which is also the receptor for the neurological hormone serotonin. The two key chemical differences between the two molecules are first, that the primary amine in serotonin is replaced with a tertiary amine in psilocin, and second, the hydroxyl group is substituted differently on the aromatic ring. Here, we find that psilocin can bind to 5-HT_2AR with an affinity higher than serotonin, and provide the molecular logic behind the higher binding affinity of psilocin using extensive molecular dynamics simulations and free energy calculations. The binding free energy of psilocin is dependent upon the protonation states of the ligands, as well as that of the key residue in the binding site: Aspartate 155. We find that the tertiary amine of psilocin, and not the altered substitution of the hydroxyl group in the ring is responsible for the increased affinity of psilocin. We propose design rules for effective antidepressants based on molecular insights from our simulations.     

Auxin structure/activity relationships: Benzoic acids and phenols

The results of self-consistent field molecular orbital calculations on auxins of the benzoic acid and phenolic types are not inconsistent with the view that a positively charged site at about 0.5 nm from an acidic group could contribute to the reversible binding of an auxin to its receptor molecule.     

A computergraphic investigation into the pharmacological role of the THC-cannabinoid phenolic moiety

There has been much debate as to the nature of the cannabinoid-receptor interaction, whether by traditional interpretation or by means of membrane perturbation. Whichever hypothesis is correct, the structural requirements for pharmacological action need determination. Here, we report a computergraphic investigation into the role of the phenolic hydroxyl moiety in such a receptor interaction. It has been determined by molecular mechanics energy calculations and volume map determinations that the proton of the hydroxyl group may be involved in hydrogen bonding at the putative receptor site.     

Heterogeneity of auxin-accumulating membrane vesicles from Cucurbita and Zea: a possible reflection of cell polarity

When microsomes from hypocotyls of Cucurbita pepo L. or coleoptiles of Zea mays L. were centrifuged on dextran-sucrose gradients a heterogeneity of auxin-accumulating vesicles was observed. Vesicles from the top part of the gradient showed saturable, specific accumulation of indole-3-acetic acid with only a small stimulation by phytotropins, and with very few binding sites for 1-N-naphthylphthalamic acid. In the vesicles from the lower part of the gradient, net accumulation of indole-3-acetic acid could be strongly increased by addition of phytotropins; binding of 1-N-naphthylphthalamic acid was high in this region. After two-phase partitioning, both kinds of vesicles were found in the upper-phase membrane fraction considered to be purified plasma membrane. The hypothesis is discussed that vesicles can be separated from the apical and basal parts of the cell's plasmalemma.Abbreviations CCO cytochrome-c oxidase - CCR KCN-insensitive NADH-dependent cytochrome-c reductase - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid - IDPase inosine 5-diphosphatase - ION3 ionophore mixture of carbonylcyanide-3-chlorophenylhydrazone, nigericin and valinomycin - 1-NAA 1-naphthaleneacetic acid - NPA 1-N-naphthylphthalamic acid - PBA 2-(1-pyrenoyl)benzoic acid - UDPG uridine diphosphoglucose     

Molecular characteristics of carbaryl, a CYP1A1 gene inducer

Carbaryl belongs to a series of compounds that activate the CYP1A1 gene. This study demonstrates the inability of carbaryl to compete with 2,3,7,8-tetrachlorodibenzo-p-dioxin for binding to the rat aryl hydrocarbon (dioxin) receptor. Structural and physicochemical properties of this insecticide, in relation to the requirements for binding to the aryl hydrocarbon receptor, are described. The crystal structure was determined experimentally using X-ray diffraction. A conformational search using molecular mechanics was performed by means of a Monte-Carlo-type method and a stochastic dynamics simulation. Lipophilicity calculations, log P, and molecular lipophilicity potential are also presented. Common and discriminating properties of carbaryl and aryl hydrocarbon receptor ligands are discussed.     

Effect of ATP analogues on the gorging response of Aedes aegypti

ABSTRACT. The ATP analogues adenylylimidodiphosphate and adenylylmethylenediphosphate are 3–5-fold more effective than ATP as gorging stimulants for Aedes aegypti. This increased potency is not due to the fact that the two analogues are not hydrolysed by the mosquito salivary apyrase, but most likely to their greater affinity to the mosquito gustatory receptor protein. The analogues 2'd ATP and 3'd ATP are about half as potent as ATP, while 2',3'-dideoxyadenosine triphosphate is 10-fold more potent than ATP in evoking the gorging response. It is proposed that removal of both hydroxyl groups eliminates binding of the stimulant at the ribose moiety, thus allowing the molecule greater freedom to rotate and bind more effectively to its two other binding sites at the amino group on the purine and at the terminal phosphate. Our data demonstrate that ATP activates the gorging response of Ae.aegypti merely by binding to its receptor protein and is not required as an exogenous source of energy. Gorging response to ATP is competitively inhibited by novobiocin.     

Sulfoglucuronyl Glycolipids Bind Laminin

Previous studies have shown that HNK-1 antibody reactive glycoconjugates, including the glycolipids 3-sulfoglucuronylneolactotetraosylceramide (SGGL-1) and 3-sulfoglucuronylneolactohexaosylceramide (SGGL-2), are temporally and spatially regulated antigens in the developing mammalian cortex. Extracellular matrix glycoprotein laminin is involved in cell adhesion by interacting with cell surface components and also promotes neurite outgrowth. Laminin has been shown to bind sulfatide. The interaction of sulfated glycolipids SGGL-1 and SGGL-2 with laminin was studied by employing a solid-phase radioimmunoassay and by HPTLC-immunoblotting. Laminin binding was detected with anti-laminin antibodies followed by 125I-labelled Protein A and autoradiography. Laminin binds SGGL-1 and SGGL-2, besides sulfatide, but does not bind significantly gangliosides and neutral glycolipids. The binding of SGGLs to laminin was two to three times less compared to sulfatide when compared on a molar basis. Desulfation of SGGLs and sulfatide by mild acid treatment resulted in abolition of laminin binding. On the other hand, chemical modification of glucuronic acid moiety by either esterification or reduction of the carboxyl group had no effect. This showed that the sulfate group was essential for laminin binding. Of the various glycosaminoglycans tested, only heparin inhibited the binding of laminin to SGGLs and sulfatide in a dose-dependent manner. This indicated that SGGLs and sulfatide bind to the heparin binding site present in the laminin molecule. The availability of HNK-1 reactive glycolipids and glycoproteins such as SGGLs and several neural cell adhesion molecules to bind laminin at critical stages of neural development may serve as important physiological signals.