Browsing by Author "Jackson, Graham E"

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    Open Access
    A single AKH neuropeptide activating three different fly AKH-receptors: an insecticide study via computational methods
    (2021) Abdulganiyyu, Ibrahim A; Jackson, Graham E; Marco, Heather G
    Flies are a widely distributed pest insect that poses a significant threat to food security. Flight is essential for the dispersal of the adult flies to find new food sources and ideal breeding spots. The supply of metabolic fuel to power the flight muscles of insects is regulated by adipokinetic hormones (AKHs). The fruit fly, Drosophila melanogaster, the flesh fly, Sarcophaga crassipalpis, and the oriental fruit fly, Bactrocera dorsalis all have the same AKH that is present in the blowfly, Phormia terraenovae; this AKH has the code-name Phote-HrTH. Binding of the AKH to the extracellular binding site of a G protein-coupled receptor causes its activation. In this thesis, the structure of Phote-HrTH in SDS micelle solution was determined using NMR restrained molecular dynamics. The peptide was found to bind to the micelle and be reasonably rigid, with an S 2 order parameter of 0.96. The translated protein sequence of the AKH receptor from the fruit fly, Drosophila melanogaster, the flesh fly, Sarcophaga crassipalpis, and the oriental fruit fly, Bactrocera dorsalis were used to construct two models for each receptor: Drome-AKHR, Sarcr-AKHR, and Bacdo-AKHR. It is proposed that these two models represent the active and inactive state of the receptor. The models based on the crystal structure of the β-2 adrenergic receptor were found to bind Phote-HrTH with a predicted binding free energy of –107 kJ mol–1 for Drome-AKHR, –102 kJ mol–1 for Sarcr-AKHR and –102 kJ mol–1 for Bacdo-AKHR. Under molecular dynamics simulation, in a POPC membrane, the β-2AR receptor-like complexes transformed to rhodopsin-like. The identification and characterisation of the ligand-binding site of each receptor provide novel information on ligand-receptor interactions, which could lead to the development of species-specific control substances to use discriminately against these pest flies.
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    Aqueous Solution Equilibria and Spectral Features of Copper Complexes with Tripeptides Containing Glycine or Sarcosine and Leucine or Phenylalanine
    (Multidisciplinary Digital Publishing Institute, 2022-01-10) Vicatos, Giselle M; Hammouda, Ahmed N; Alnajjar, Radwan; Bonomo, Raffaele P; Valora, Gabriele; Bourne, Susan A; Jackson, Graham E
    Copper(II) complexes of glycyl-L-leucyl-L-histidine (GLH), sarcosyl-L-leucyl-L-histidine (Sar-LH), glycyl-L-phenylalanyl-L-histidine (GFH) and sarcosyl-L-phenylalanyl-L-histidine (Sar-FH) have potential anti-inflammatory activity, which can help to alleviate the symptoms associated with rheumatoid arthritis (RA). From pH 2–11, the MLH, ML, MLH-1 and MLH-2 species formed. The combination of species for each ligand was different, except at the physiological pH, where CuLH-2 predominated for all ligands. The prevalence of this species was supported by EPR, ultraviolet-visible spectrophotometry, and mass spectrometry, which suggested a square planar CuN4 coordination. All ligands have the same basicity for the amine and imidazole-N, but the methyl group of sarcosine decreased the stability of MLH and MLH-2 by 0.1–0.34 and 0.46–0.48 log units, respectively. Phenylalanine increased the stability of MLH and MLH-2 by 0.05–0.29 and 1.19–1.21 log units, respectively. For all ligands, 1H NMR identified two coordination modes for MLH, where copper(II) coordinates via the amine-N and neighboring carbonyl-O, as well as via the imidazole-N and carboxyl-O. EPR spectroscopy identified the MLH, ML and MLH-2 species for Cu-Sar-LH and suggested a CuN2O2 chromophore for ML. DFT calculations with water as a solvent confirmed the proposed coordination modes of each species at the B3LYP level combined with 6-31++G**.
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    Capsular polysaccharide conformations in pneumococcal serotypes 19F and 19A
    (Elsevier, 2015) Kuttel, Michelle M; Jackson, Graham E; Mafata, Mpho; Ravenscroft, Neil
    Streptococcus pneumoniae is a significant pathogen in children. Although the PCV7 pneumococcal conjugate vaccine has reduced pneumococcal disease, non-vaccine serotype 19A infection has increased, despite expectations of cross-protection from vaccine serotype 19F. Serotype 19A is included in the new PCV13 vaccine, but not in PCV10. In the solution simulations of 19F and 19A oligosaccharide chains reported here, both polysaccharides form unstructured random coils, with inflexible repeat units linked by mobile phosphodiester linkages. However, there are clear conformational differences. In the 19F repeat unit, the rhamnose residue is nearly orthogonal to the other residues, whereas 19A has residues in similar orientations. This finding is corroborated by key inter-residue distances calculated from NMR NOESY experiments. Further, 19F is predominantly in extended conformations, whereas 19A exhibits a high prevalence of tight hairpin bends. These conformational differences may account for a lack of antibody cross-protection between serotypes 19F and 19A.
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    Open Access
    Computer simulation of nickel in blood-plasma following the in vitro investigations of complex formation chemistry with polyamine(amide) ligands
    (Royal Society of Chemistry, 2004) Nomkoko, Edmund T; Jackson, Graham E; Nakani, Bandile S; Bourne, Susan A
    In- and out-of-cell potentiometric techniques have been used to determine the formation constants for nickel(II) with 3,3,9,9-tetramethyl-4,8-diazaundecane-2,10-dione dioxime (L1), N,N′-bis(2-hydroxyiminopropionyl)propane-1,3-diamine (L2) and 1,15-bis(N,N-dimethyl)-5,11-dioxo-8-(N-benzyl)-1,4,8,12,15-pentaazapentadecane (L3) at 25 °C and an ionic strength of 0.15 mol dm−3. Nickel(II) forms stable complexes with L1 and L2 where square-planar [NiLH−1] and [NiLH−2] species predominate under alkaline conditions. The square-planar coordination of nickel by L1 has been confirmed by a single-crystal X-ray structure, UV/Vis spectrometry and molecular mechanics calculations of the [NiL1H−1] complex. The introduction of a third amine group into L3 dramatically decreases the ligand's ability to complex Ni(II). This results from a change in structure of the complex which decreases the ability of the metal ion to promote the dissociation of the amide protons. Using a model of blood plasma, the high binding ability of L1 towards Ni(II) is calculated to decrease the mobilisation of Cu(II) in plasma by approximately 65%. [CuL1H−1] is currently under investigation as an anti-inflammatory agent.
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    Open Access
    Development of copper peptide complexes as anti-Inflammatory drugs
    (2015) Hammouda, Ahmed N H; Jackson, Graham E
    Copper complexes have been reported to have anti-inflammatory activities for the alleviation of inflammation associated with rheumatoid arthritis (RA). The present study focuses on the design of new drugs that could be used to change the bioavailability of copper and hence alleviate inflammation. The ligands chosen were sarcosyl-L-histidyl-L-lysine, sarcosyl-Llysyl- L-histidine, sarcosyl-L-histidyl-L-histidine, sarcosyl-L-lysyl-L-lysine and sarcosyl-Lglycyl- L-histidine. Equilibrium constants of H+, Cu(II), Ni(II) and Zn(II) with the peptides were measured in aqueous solution at 25±0.01oC and an ionic strength of 0.15M (NaCl) using glass electrode potentiometry. The tripeptides species showed significantly different coordination behaviour. The results that Cu(II) coordinates to one amino group, two deprotonated peptides and one imidazole nitrogen atoms to give a neutral complex. The structures of the complex species were investigated using ultraviolet-visible (Uv-Vis), nuclear magnetic resonance (NMR), electrospray ionisation mass spectrometry (ESI-MS) spectroscopy as well as molecular mechanics (MM) calculations. The visible spectra obtained for the different species in solution were typical of Cu(II) and Ni(II) complexes. 1H NMR identified the active binding sites to be the imidazole nitrogen, the amide nitrogen and the terminal amino group. The imidazole nitrogen was involved in coordination first, followed by the amide and then the terminal amine groups. The ԑ-amino group of lysine did not coordinate to the Cu(II). Molecular mechanics was used to support the Cu(II) structures postulated from potentiometric and spectroscopic data. The prefered method of increasing the available pool of low molecular weight Cu(II) species in vivo is via dermal absorption. For this reason the drugs were designed so that they could be administered dermally and be selective for Cu(II) so that they do not affect the speciation of other metal ions in blood plasma. Speciation calculations of Cu(II) using a computer model of blood plasma indicated that Sar-Lys-His was the best at mobilising copper in vivo. This study also considered percutaneous skin absorption. Octanol/water partition coefficients and Franz cell permeation studies showed that the Cu(II) complexes are hydrophilic but that Sar-Gly-His caused a 2 fold increase in membrane permeability of Cu(II).
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    Development of dermally absorbed copper(ii) complexes as potential anti-inflammatory drugs
    (2021) Vicatos, Giselle Marianthi; Jackson, Graham E; Bourne, Susan A
    Rheumatoid arthritis (RA) is a debilitating disease affecting 5% of the world's population and there is no cure. Copper(II) complexes have been reported to have anti-inflammatory activity and alleviate the symptoms associated with the disease. The present study focuses on the design of new drugs that could be used to change the bioavailability of copper(II) and hence alleviate the inflammation. The tripeptides, glycyl-L-leucyl-L-histidine (GLH), sarcosyl-L-leucyl-Lhistidine (Sar-LH), glycyl-L-phenylalanyl-L-histidine (GFH) and sarcosyl-L-phenylalanyl-Lhistidine (Sar-FH) were designed to resemble the natural in vivo copper(II) transporter, human serum albumin, so that they could be selective for copper(II). The preferred route of administration is dermal absorption and so sarcosine was added to improve the lipophilicity of the drug. This administration method was chosen since it is both nonharmful and convenient for patients. The stability of the complexes was measured using glass electrode potentiometry and their solution structure studied using UV-Vis spectrophotometry, CW-EPR spectroscopy, 1H NMR, ESI-MS and molecular modelling calculations. The presence of sarcosine did not significantly affect the stability of the complexes. Several species were found to exist in solution depending on the pH, but at pH 7, the CuLH-2 species predominated for all four tripeptides. In this species, the ligand was found to coordinate to copper(II) via the terminal amine-N, the two amide-Ns and imidazole-N, in a square planar geometry. Using a computer model of blood plasma, all four ligands were found to mobilise copper(II), without disrupting the homeostasis of nickel(II), zinc(II) or calcium(II) in the order of GFH > Sar-FH > GLH > Sar-LH. GFH increased the low molecular mass copper(II) species by 40.7 times at 0.1 mM. The lipophilicity of the complexes was estimated by measuring their octanol/water partition coefficients. All the complexes were found to be hydrophilic with log Poct/aq ranging from -3 to -2. Dermal absorption was estimated using an artificial membrane and a Franz cell. Only a moderate increase in membrane permeability of copper(II) was found. The stability of the copper(II) complexes, their ability to mobilise copper(II) from endogenous sources and their improved dermal absorption, justifies further testing of this class of ligand as potential, dermally absorbable, anti-inflammatory drugs.
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    In Silico Screening for Pesticide Candidates against the Desert Locust Schistocerca gregaria
    (Multidisciplinary Digital Publishing Institute, 2022-03-07) Jackson, Graham E; Gäde, Gerd; Marco, Heather G
    Adipokinetic hormone (AKH) is one of the most important metabolic neuropeptides in insects, with actions similar to glucagon in vertebrates. AKH regulates carbohydrate and fat metabolism by mobilizing trehalose and diacylglycerol into circulation from glycogen and triacylglycerol stores, respectively, in the fat body. The short peptide (8 to 10 amino acids long) exerts its function by binding to a rhodopsin-like G protein-coupled receptor located in the cell membrane of the fat body. The AKH receptor (AKHR) is, thus, a potential target for the development of novel specific (peptide) mimetics to control pest insects, such as locusts, which are feared for their prolific breeding, swarm-forming behavior and voracious appetite. Previously, we proposed a model of the interaction between the three endogenous AKHs of the desert locust, Schistocerca gregaria, and the cognate AKHR (Jackson et al., Peer J. 7, e7514, 2019). In the current study we have performed in silico screening of two databases (NCI Open 2012 library and Zinc20) to identify compounds which may fit the endogenous Schgr-AKH-II binding site on the AKHR of S. gregaria. In all, 354 compounds were found to fit the binding site with glide scores < −8. Using the glide scores and binding energies, 7 docked compounds were selected for molecular dynamic simulation in a phosphatidylcholine membrane. Of these 7 compounds, 4 had binding energies which would allow them to compete with Schgr-AKH-II for the receptor binding site and so are proposed as agonistic ligand candidates. One of the ligands, ZINC000257251537, was tested in a homospecific in vivo biological assay and found to have significant antagonistic activity.
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    Metal complexes of anti-tubercular drugs
    (2018) Dauda, Khadijah Tolulope; Caira, Mino; Jackson, Graham E
    There is a continuing need to improve anti-tubercular drugs due to the development of resistance towards existing drugs. In some cases, metal complexes are known to improve the bioavailability of drugs. Hence the present study looks at the use of metal complexes of anti-tubercular drugs to improve the permeability and bioavailability of the drugs. The anti-tubercular drugs isoniazid (ISO), ethambutol (EMB), para-aminosalicylic acid (PAS), rifampicin (RFN) and pyrazinecarboxamide (PZA) were used in this study. Since the solubility and hence permeability and bioavailability of the drugs depend on their solution speciation, the equilibrium constants for the reaction of H+ , Cu(II), Ni(II) and Zn(II) with the ligands were measured, in aqueous solution, at 25  0.01C and an ionic strength of 0.15 M (NaCl) using glass electrode potentiometry. The structures of the complexes with EMB, ISO and PAS were investigated using ultravioletvisible spectroscopy. The visible spectra obtained for the different species of EMB in solution were typical of Cu(II) and Ni(II) complexes. The spectra found for the various species of ISO and PAS in solution were also characteristic of their Cu(II) complexes. The results from the visible spectra support the structures postulated from the potentiometric data. This study also considered membrane permeability and absorption using a Franz cell and octanol/water partition coefficients. Partition coefficient studies showed that ISO and PZA and their complexes are hydrophilic while RFN and PAS and their complexes are lipophilic. The incorporation of a metal-ion improves the lipophilicity/hydrophilicity properties of the ligand. The presence of metal greatly enhanced the permeation of ISO through an artificial membrane in the order Cu(II) > Zn(II) > Ni(II) > ISO. A significant improvement was also found when Cu(II) was incorporated into the RFN system with an enhancement factor of 20. Zn(II) was vii able to improve the permeation of PAS with an enhancement ratio of 2. The incorporation of Cu(II), Ni(II) and Zn(II) does not affect the flux and permeability coefficient of PZA. Since the drugs are administered in tablet form, attempts were made to synthesise the metal complexes of the drugs in solid form. X-ray crystallography could then be used to confirm the solution structures. Co-precipitation, refluxing and mechanochemical methods (neat and liquid-assisted co-grinding) were employed to synthesise Cu(II), Ni(II) and Zn(II) complexes of the series of anti-tubercular drugs. However, despite exhaustive efforts, all experiments resulted in the formation of only physical mixtures of the reactants, as revealed by chromatographic and X-ray diffraction methods. This impelled the use of the solvothermal method as an alternative technique. ISO and PZA metal complexes were synthesised via this method. Unexpected products were obtained, as indicated unambiguously by single crystal Xray diffraction, and a probable mechanism for their formation was postulated. The incorporation of metals into anti-tubercular drugs has a significant influence in improving the permeability of the parent drug. It was found that the presence of Cu(II), Ni(II) and Zn(II) improved the permeability coefficient of ISO, while Cu(II) improved RFN and Zn (II) enhanced that of PAS.