Browsing by Author "Torres, AM"

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    Determination of Na+ binding parameters by relaxation analysis of selected 23Na NMR coherences: RNA, BSA and SDS
    (John Wiley & Sons, 2005-03) Torres, AM; Philp, DJ; Kemp-Harper, R; Garvey, CJ; Kuchel, PW
    Nuclear magnetic resonance provides several unique means of investigating the interactions between different inorganic ions and various macromolecules. 23Na is a quadrupolar nucleus, meaning that relaxation analysis of the various coherences allows the measurement of its binding to biological macromolecules. In this study, we analyzed the quadrupolar relaxation of 23Na+ longitudinal magnetization and single- and triple-quantum coherences in aqueous systems containing RNA, bovine serum albumin and sodium dodecyl sulfate micelles. The effectiveness of the James-Noggle method for determining binding constants was evaluated in these systems, and also the applicability of various 23Na coherences in providing information on the extent and affinity of binding to the three different classes of biomolecules. © 2004, John Wiley & Sons Ltd.
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    Photocatalytic properties of Ta-doped TiO2
    (Springer Nature, 2017-06-10) Alim, MA; Bak, T; Atanacio, AJ; Ionescu, M; Kennedy, BJ; Price, WS; Du Plessis, J; Pourmahdavi, M; Zhou, MF; Torres, AM; Nowotny, J
    This work reports the effect of tantalum (0.1–1 at.% Ta) on the photocatalytic performance of TiO2 annealed at 1373 and 1673 K in air. It was shown that addition of tantalum resulted in an increase of photocatalytic activity of TiO2 for the specimens annealed at 1373 K. However, the activity of the Ta-doped TiO2 specimens annealed at 1673 K was reduced. The effect of tantalum on the photocatalytic performance at 1373 K was rationalised in terms of an increased concentration of titanium vacancies acting as the active surface sites, and increased charge transport. In this work, it was also shown that the band gap reduction due to tantalum incorporation had little effect on photocatalytic performance. The effect of annealing at 1673 K on photocatalytic activity was explained in terms of reduced surface segregation of tantalum. © 2017 Springer Nature Switzerland AG.
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    Platypus venom: source of novel compounds
    (CSIRO Publishing, 2009-10) Koh, JMS; Bansal, PS; Torres, AM; Kuchel, PW
    An anatomical feature of the platypus (Ornithorhynchus anatinus) that is seen in only one other mammal, the echidna, is that the male has a crural glandular system that produces venom that is used for defence and territorial-breeding functions; whether the echidna is similarly venomous is not yet established. Platypus venom contains many novel proteins and peptides that are different from those in reptilian venom. It also causes pain and symptoms that are not experienced by any other kind of envenomation. Five types of proteins and peptides have been isolated and identified from platypus venom, namely: defensin-like peptides (DLPs); Ornithorhynchus venom C-type natriuretic peptides (OvCNPs); Ornithorhynchus nerve growth factor; hyaluronidase; and L-to-D-peptide isomerase. The structures of DLPs and OvCNPs have already been studied and they are very similar to b-defensin-12 and mammalian C-type natriuretic peptides, respectively. A special mammalian L-to-D-peptide isomerase that is responsible for interconverting the L-and D-peptide isomers is also found in platypus venom. Isomerase activity has recently been discovered in platypus tissues other than the venom gland. It is possible that similar kinds of enzymes might exist in other mammals and play important, as yet unknown, biological roles. Considering the fact that some animal venoms have already been widely used in pharmaceutical applications, research into platypus venom may lead to the discovery of new molecules and potent drugs that are useful biomedical tools. © 2009, CSIRO Publishing
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    Pore domain outer helix contributes to both activation and inactivation of the hERG K+ channel
    (American Society for Biochemistry and Molecular Biology, 2009-01-09) Ju, P; Pages, G; Riek, RP; Chen, PC; Torres, AM; Bansal, PS; Kuyucak, S; Kuchel, PW; Vandenberg, JI
    Ion flow in many voltage-gated K+ channels (VGK), including the (human ether-a-go-go-related gene) hERG channel, is regulated by reversible collapse of the selectivity filter. hERG channels, however, exhibit low sequence homology to other VGKs, particularly in the outer pore helix (S5) domain, and we hypothesize that this contributes to the unique activation and inactivation kinetics in hERG K+ channels that are so important for cardiac electrical activity. The S5 domain in hERG identified by NMR spectroscopy closely corresponded to the segment predicted by bioinformatics analysis of 676 members of the VGK superfamily. Mutations to approximately every third residue, from Phe(551) to Trp(563), affected steady state activation, whereas mutations to approximately every third residue on an adjacent face and spanning the entire S5 segment perturbed inactivation, suggesting that the whole span of S5 experiences a rearrangement associated with inactivation. We refined a homology model of the hERG pore domain using constraints from the mutagenesis data with residues affecting inactivation pointing in toward S6. In this model the three residues with maximum impact on activation (W563A, F559A, and F551A) face out toward the voltage sensor. In addition, the residues that when mutated to alanine, or from alanine to valine, that did not express (Ala(561), His(562), Ala(565), Trp(568), and Ile(571)), all point toward the pore helix and contribute to close hydrophobic packing in this region of the channel. © 2009, American Society for Biochemistry and Molecular Biology
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    Structure of the pore-helix of the hERG K+ channel
    (Springer, 2009-12) Pages, G; Torres, AM; Ju, P; Bansal, PS; Alewood, PF; Kuchel, PW; Vandenberg, JI
    The hERG K+ channel undergoes rapid inactivation that is mediated by 'collapse' of the selectivity filter, thereby preventing ion conduction. Previous studies have suggested that the pore-helix of hERG may be up to seven residues longer than that predicted by homology with channels with known crystal structures. In the present work, we determined structural features of a peptide from the pore loop region of hERG (residues 600-642) in both sodium dodecyl sulfate (SDS) and dodecyl phosphocholine (DPC) micelles using NMR spectroscopy. A complete structure calculation was done for the peptide in DPC, and the localization of residues inside the micelles were analysed by using a water-soluble paramagnetic reagent with both DPC and SDS micelles. The pore-helix in the hERG peptide was only two-four residues longer at the N-terminus, compared with the pore helices seen in the crystal structures of other K+ channels, rather than the seven residues suggested from previous NMR studies. The helix in the peptide spanned the same residues in both micellar environments despite a difference in the localization inside the respective micelles. To determine if the extension of the length of the helix was affected by the hydrophobic environment in the two types of micelles, we compared NMR and X-ray crystallography results from a homologous peptide from the voltage gated potassium channel, KcsA. © 2009, Springer.