283 results for Brimble, Margaret, ResearchSpace@Auckland

  • MALDI-imaging enables direct observation of kinetic and thermodynamic products of mixed peptide fiber assembly

    Medini, Karima; West, Brandi; Williams, David; Brimble, Margaret; Gerrard, Juliet (2017-02)

    Journal article
    The University of Auckland Library

    Controlling the self-assembly of multicomponent systems provides a key to designing new materials and understanding the molecular complexity of biology. Here, we demonstrate the first use of MALDI-imaging to characterize a multicomponent self-assembling peptide fiber. Observations of mixed peptide systems over time demonstrate how simple sequence variation can change the balance between kinetic and thermodynamic products.

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  • Characterizing the mode of action of extracellular Connexin43 channel blocking mimetic peptides in an in vitro ischemia injury model.

    Kim, Y; Griffin, Jarred; Harris, PWR; Chan, SHC; Nicholson, Louise; Brimble, Margaret; OCarroll, Simon; Green, Colin (2017-02)

    Journal article
    The University of Auckland Library

    Non-selective Connexin43 hemichannels contribute to secondary lesion spread. The hemichannel blocking peptidomimetic Peptide5, derived from the second extracellular loop of the human Connexin43 protein, prevents lesion spread and reduces vascular permeability in preclinical models of central nervous system injury. The molecular mode of action of Peptide5, however, was unknown and is described here.Human cerebral microvascular endothelial cells and APRE-19 cells were used. Scrape loading was used to assess gap junction function and hypoxic, acidic ion-shifted Ringer solution induced ATP release used to assess hemichannel function. Peptide modifications, including amino acid substitutions and truncations, and competition assays were used to demonstrate Peptide5 functional specificity and site of action respectively.Peptide5 inhibits Connexin43 hemichannel-mediated ATP release by acting on extracellular loop two of Connexin43, adjacent to its matching sequence within the protein. Precise sequence specificity is important for hemichannel block, but less so for uncoupling of gap junction channels (seen only at high concentrations). The SRPTEKT motif is central to Peptide5 function but on its own is not sufficient to inhibit hemichannels. Both the SRPTEKT motif and Peptide5 reduce gap junction communication, but neither uncoupling below 50%.Reduced gap junction coupling at high peptide concentrations appears to be relatively non-specific. However, Peptide5 at low concentrations acts upon extracellular loop two of Connexin43 to block hemichannels in a precise, sequence specific manner.The concentration dependent and sequence specific action of Peptide5 supports its development for the treatment of retinal injury and chronic disease, as well as other central nervous system injury and disease conditions.

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  • An Efficient Chemical Synthesis of Lassomycin Enabled by an On-Resin Lactamisation?Off-Resin Methanolysis Strategy and Preparation of Chemical Variants

    Harris, Paul; Cook, GM; Leung, Ka Ho Ivanhoe; Brimble, Margaret (2017)

    Journal article
    The University of Auckland Library

    An efficient synthesis of the naturally occurring cyclic peptide lassomycin that bears a unique Asp???Gly isopeptide bond and a C-terminal methyl ester is described. On-resin cyclisation between 1Gly and side chain 8Asp and a subsequent solution-phase transesterification reaction afforded synthetic lassomycin in high yield. Several analogues were also prepared using the optimised methodology. None of the cyclised peptides, including the synthetic natural product, exhibited any significant activity against Mycobacterium tuberculosis. Comparison of the spectroscopic data for synthetic lassomycin with naturally occurring lassomycin concluded they were otherwise identical.

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  • Multifunctional thermoresponsive designer peptide hydrogels

    De Leon Rodriguez, Luis Manuel; Hemar, Yacine; Mo, G; Mitra, Alok; Cornish, Jillian; Brimble, Margaret (2017-01-01)

    Journal article
    The University of Auckland Library

    We report the synthesis and characterization of multifunctional peptides comprised of a hydrogel forming ??-sheet peptide segment and a matrix metalloproteinase 2 substrate containing a propargylglycinyl linker that is further derivatized with an RGD peptide sequence via ???click??? chemistry. In contrast to currently known systems, these multifunctional peptides formed gels that are stiffer than those formed by their respective precursors. All the peptides showed reversible thermoresponsive properties, which render them as suitable lead systems for a variety of possible biomedical applications. Statement of Significance In general, it has been frequently observed that chemical biofunctionalization of peptide hydrogels adversely affects peptide assembly, hydrogel formation or mechanical properties, which severely compromises their application. A functionalization protocol that allows to generate peptide hydrogels that display significantly improved mechanical properties over their unfunctionalized counterparts is reported in this work. These peptides also showed thermoresponsive viscoelastic characteristics, including an example of a peptide hydrogel that displays lower critical solution temperature behaviour.

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  • Controlling gelation with sequence: towards programmable peptide hydrogels

    Medini, Karima; Mansel, BW; Williams, MA; Brimble, Margaret; Williams, David; Gerrard, Juliet (2016-10-01)

    Journal article
    The University of Auckland Library

    The self-assembling peptide IKHLSVN, inspired by inspection of a protein-protein interface, has previously been reported as one of a new class of bio-inspired peptides. Here the peptide, dubbed littleSven, and modifications designed to probe the resilience of the sequence to self-assembly, is characterised. Although the parent peptide did not form a hydrogel, small modifications to the sequence (one side chain or an N-terminus modification) led to hydrogels with properties (eg. gelation time and rheology) that could be tuned by these small alterations. The results suggest that peptides derived from protein-protein interfaces are resilient to changes in sequence and can be harnessed to form hydrogels with controlled properties.Natural occurring self-assembly peptides are attractive building blocks for engineered bionanomaterials due to their biocompatibility and biodegradability. The bio-inspired self-assembly peptide, IKHLSVN, was used as a template to design peptides that readily formed hydrogels. The peptide sequence was specifically tuned to create a bionanomaterial with different properties that could be exploited downstream for a broad range of applications: nanowires, drug release, vaccine adjuvant, tissue engineering. We describe how small modifications to the parent peptide alter the amyloid-like characteristics and gel strength for each peptide.

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  • Pyranonaphthoquinones ??? isolation, biology and synthesis: an update

    Naysmith, BJ; Hume, Paul; Sperry, Jonathan; Brimble, Margaret (2017-01)

    Journal article
    The University of Auckland Library

    Covering: 2008 to 2015. A review on the isolation, biological activity and synthesis of pyranonaphthoquinone natural products from 2008-2015 is providedThis review discusses the isolation, biological activity and synthesis of pyranonaphthoquinone natural products, covering the years 2008-2015. The pyranonaphthoquinones are a group of metabolites sharing a common naphtho[2,3-c]pyran-5,10-dione ring system that have been isolated from a wide range of microorganisms, plants and insects. In addition to their synthetically challenging molecular structures, pyranonaphthoquinones exhibit a wide array of biological activity, including anti-bacterial, anti-fungal and anti-cancer properties. The therapeutic potential of these compounds has led to a dynamic interplay between total synthesis and biological evaluation.

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  • Isolation, Structural Elucidation, and Synthesis of Lepteridine From Manuka (Leptospermum scoparium) Honey

    Daniels, BJ; Prijic, G; Meidinger, Sarah; Loomes, Kerry; Stephens, JM; Schlothauer, RC; Furkert, Daniel; Brimble, Margaret (2016-06)

    Journal article
    The University of Auckland Library

    Ma??nuka honey, made from the nectar of Leptospermum scoparium, has garnered scientific and economical interest due to its nonperoxide antibacterial activity. Biomarkers for genuine ma??nuka honey are increasingly in demand due to the presence of counterfeit ma??nuka honey. This work reports the identification of a compound previously unreported in ma??nuka honey by HPLC, and determination of the structure of the as 3,6,7-trimethyllumazine using NMR, MS, IR, and UV/vis spectroscopy. This assignment was confirmed by total synthesis. The natural product, renamed lepteridine, was only observed in ma??nuka honeys and could potentially serve as a biomarker for genuine ma??nuka honey.

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  • Radiation Damage and Racemic Protein Crystallography Reveal the Unique Structure of the GASA/Snakin Protein Superfamily

    Yeung, Ho; Squire, Christopher; Yosaatmadja, Yuliana; Panjikar, S; L??pez, G; Molina, A; Baker, Edward; Harris, Paul; Brimble, Margaret (2016-07-04)

    Journal article
    The University of Auckland Library

    Proteins from the GASA/snakin superfamily are common in plant proteomes and have diverse functions, including hormonal crosstalk, development, and defense. One 63-residue member of this family, snakin-1, an antimicrobial protein from potatoes, has previously been chemically synthesized in a fully active form. Herein the 1.5 ?? structure of snakin-1, determined by a novel combination of racemic protein crystallization and radiation-damage-induced phasing (RIP), is reported. Racemic crystals of snakin-1 and quasi-racemic crystals incorporating an unnatural 4-iodophenylalanine residue were prepared from chemically synthesized d- and l-proteins. Breakage of the C???I bonds in the quasi-racemic crystals facilitated structure determination by RIP. The crystal structure reveals a unique protein fold with six disulfide crosslinks, presenting a distinct electrostatic surface that may target the protein to microbial cell surfaces.

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  • Synthesis of Psychrophilin E

    Ngen, STY; Kaur, Harveen; Hume, Paul; Furkert, Daniel; Brimble, Margaret (2016)

    Journal article
    The University of Auckland Library

    The first total synthesis of psychrophilin E, a potent antiproliferative cyclic tripeptide isolated from Aspergillus versicolor ZLN-60, is reported herein. Key features of the synthesis include the installation of an amide bond between the indole-nitrogen of tryptophan and an anthranilic acid residue, and a high yielding macrolactamization of the linear tripeptide to the desired macrocycle.

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  • Structure-mechanical property correlations of hydrogel forming ??-sheet peptides

    De Leon Rodriguez, Luis Manuel; Hemar, Yacine; Cornish, Jillian; Brimble, Margaret (2016-09-07)

    Journal article
    The University of Auckland Library

    Peptide based hydrogels have received much attention due to their potential biomedical applications. The majority of the gel forming peptides present a ??-sheet motif that is composed of alternating hydrophobic/hydrophilic amino acids. Furthermore, structural characterization of the assembly of these ??-sheet peptides has been refined recently. However, the relationship between peptide residue composition, molecular structure and the mechanical properties of the resulting hydrogel is not entirely understood. In this review, an analysis of the structural features of different ??-sheet peptide hydrogels and their mechanical properties is discussed, in order to provide further insight on the molecular features that are relevant for the design of effective ??-peptide hydrogels.

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  • Synthesis and in vitro bone cell activity of analogues of the cyclohexapeptide dianthin G

    Amso, Zaid; Kowalczyk, Renata; Park, Young Eun; Watson, M; Lin, Jian; Musson, David; Cornish, Jillian; Brimble, Margaret (2016-07-14)

    Journal article
    The University of Auckland Library

    The cyclohexapeptide natural product dianthin G promotes osteoblast (bone-forming cell) proliferation in vitro at nanomolar concentrations, and is therefore considered a promising candidate for the treatment of osteoporosis. An N(??)-methyl amide bond scan of dianthin G was performed to probe the effect of modifying amide bonds on osteoblast proliferation. In addition, to provide greater structural diversity, a series of dicarba dianthin G analogues was synthesised using ring closing metathesis. Dianthin G and one novel dicarba analogue increased the number of human osteoblasts and importantly they did not increase osteoclast (bone-resorbing cell) differentiation in bone marrow cells.

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  • Synthesis and biological evaluation of the osteoblast proliferating cyclic peptides dianthins G and H

    Kaur, Harveen; Heapy, AM; Kowalczyk, Renata; Amso, Z; Watson, Maureen; Cornish, Jillian; Brimble, Margaret (2014-10-21)

    Journal article
    The University of Auckland Library

    The first synthesis and osteoblast proliferative activity of the naturally occurring cyclic peptides dianthins G and H is described. The greater potency of naturally occurring dianthin G over dianthin H at physiological concentrations mirrored the osteoblast proliferative activity observed for synthetic dianthins G and H. Six alanine-scan analogues of the more potent dianthin G were also synthesised and osteoblast assays revealed that four of the six residues can be further modified for improved activity. We also confirmed by variable temperature 1H NMR spectroscopic analysis that the sets of major and minor signals observed for dianthins G and H in DMSO-d6 are in fact due to cis???trans rotational isomers of the proline ring.

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  • Synthesis of truncated analogues of preptin-(1-16), and investigation of their ability to stimulate osteoblast proliferation

    Kowalczyk, Renata; Yang, Sung Hyun; Brimble, Margaret; Callon, Karen; Watson, Maureen; Park, Y-E; Cornish, Jillian (2014-07-15)

    Journal article
    The University of Auckland Library

    Preptin, a 34-amino acid residue peptide hormone is co-secreted with insulin from the ??-pancreatic cells and is active in fuel metabolism. We have previously established that a shorter fragment of preptin, namely preptin-(1???16), stimulates bone growth by proliferation and increasing the survival rate of osteoblasts. This was demonstrated in both in vitro and in vivo models. These findings suggest that preptin-(1???16) could play an important role in the anabolic therapy of osteoporosis. However, due to the large size of the peptide it is not an ideal therapeutic agent. The aim of this study was to identify the shortest preptin analogue that retains or even increases the bone anabolic activity as compared to the parent preptin-(1???16) peptide. Truncations were made in a methodical manner from both the N-terminus and the C-terminus of the peptide, and the effect of these deletions on the resulting biological activity was assessed. In order to improve the enzymatic stability of the shortest yet active analogue identified, ruthenium-catalysed ring closing metathesis was used to generate a macrocyclic peptide using allylglycine residues as handles for ring formation. We have successfully identified a short 8-amino acid preptin (1???8) fragment that retains an anabolic effect on the proliferation of primary rat osteoblasts and enhances bone nodule formation. Preptin (1???8) is a useful lead compound for the development of orally active therapeutics for the treatment of osteoporosis.

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  • Structure activity relationship study on the peptide hormone preptin, a novel bone-anabolic agent for the treatment of osteoporosis

    Amso, Z; Kowalczyk, Renata; Watson, M; Park, YE; Callon, Karen; Musson, David; Cornish, Jillian; Brimble, Margaret (2016-10-21)

    Journal article
    The University of Auckland Library

    Preptin is a 34-residue pancreatic hormone shown to be anabolic to bone in vitro and in vivo. The bone activity of preptin resides within the (1-16) N-terminal fragment. Due to its peptidic nature, the truncated fragment of preptin is enzymatically unstable; however it provides an attractive framework for the creation of stable analogues using various peptidomimetic techniques. An alanine scan of preptin (1-16) was undertaken which showed that substitution of Ser at position 3 or Pro at position 14 did not inhibit the proliferative activity of preptin in primary rat osteoblasts (bone-forming cells). Importantly, Ser-3 to Ala substitution also showed a significant activity on osteoblast differentiation in vitro and increased the formation of mineralised bone matrix. Additional modifications with non-proteinogenic amino acids at position 3 improved the stability in liver microsomes, but diminished the osteoblast proliferative activity. In addition, to provide greater structural diversity, a series of macrocyclic preptin (1-16) analogues was synthesised using head-to-tail and head-to-side chain macrolactamisation as well as ring-closing metathesis. However, a detrimental effect on osteoblast activity was observed upon macrocyclisation.

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  • Synthesis and evaluation of disulfide bond mimetics of amylin-(1-8) as agents to treat osteoporosis

    Kowalczyk, Renata; Harris, Paul; Brimble, Margaret; Callon, Karen; Watson, Maureen; Cornish, Jillian (2012-04-15)

    Journal article
    The University of Auckland Library

    Osteoporotic fracture is a significant public health problem, resulting in fractures in >50% of women and in almost one third of men age 65 and older. Most of the existing therapies act by slowing bone loss, through inhibiting the action of bone resorbing cells. However, more substantial reductions of fracture numbers will only result from treatments that can rebuild bone. Our own animal studies demonstrated the anabolic potential of the small but unstable octapeptide fragment of amylin-(1-37), namely amylin-(1-8) containing one disulfide bridge (Cys/2 and Cys/7) [Am. J. Physiol. Endocrinol. Metab. 2000, 279, E730]. Herein, we describe the synthesis of amylin-(1-8) octapeptide and seven analogues thereof wherein the disulfide bridge is modified either via insertion of different linkers or bridges of a different nature in order to improve the stability and/or bone anabolic activity of the parent peptide. The peptide analogues were screened for proliferative activity in primary foetal rat bone-forming cells or osteoblasts at physiological concentrations. One such analogue showed promising biological activity.

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  • Receptor Activity-modifying Proteins 2 and 3 Generate Adrenomedullin Receptor Subtypes with Distinct Molecular Properties

    Watkins, HA; Chakravarthy, M; Abhayawardana, RS; Gingell, Joseph; Garelja, Michael; Pardamwar, M; McElhinney, JMWR; Lathbridge, A; Constantine, A; Harris, Paul; Yuen, TY; Brimble, Margaret; Barwell, J; Poyner, DR; Woolley, MJ; Conner, AC; Pioszak, AA; Reynolds, Christopher; Hay, Deborah (2016-05-27)

    Journal article
    The University of Auckland Library

    Adrenomedullin (AM) is a peptide hormone with numerous effects in the vascular systems. AM signals through the AM1 and AM2 receptors formed by the obligate heterodimerization of a G protein-coupled receptor, the calcitonin receptor-like receptor (CLR), and receptor activity-modifying proteins 2 and 3 (RAMP2 and RAMP3), respectively. These different CLR-RAMP interactions yield discrete receptor pharmacology and physiological effects. The effective design of therapeutics that target the individual AM receptors is dependent on understanding the molecular details of the effects of RAMPs on CLR. To understand the role of RAMP2 and -3 on the activation and conformation of the CLR subunit of AM receptors, we mutated 68 individual amino acids in the juxtamembrane region of CLR, a key region for activation of AM receptors, and determined the effects on cAMP signaling. Sixteen CLR mutations had differential effects between the AM1 and AM2 receptors. Accompanying this, independent molecular modeling of the full-length AM-bound AM1 and AM2 receptors predicted differences in the binding pocket and differences in the electrostatic potential of the two AM receptors. Druggability analysis indicated unique features that could be used to develop selective small molecule ligands for each receptor. The interaction of RAMP2 or RAMP3 with CLR induces conformational variation in the juxtamembrane region, yielding distinct binding pockets, probably via an allosteric mechanism. These subtype-specific differences have implications for the design of therapeutics aimed at specific AM receptors and for understanding the mechanisms by which accessory proteins affect G protein-coupled receptor function.

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  • Enantioselective Synthesis of BE Ring Analogues of Methyllycaconitine

    Dickson, E; Pilkington, L; Brimble, Margaret; Barker, David (2016-01-21)

    Journal article
    The University of Auckland Library

    The enantioselective synthesis of decahydroquinolines mimicking the BE rings of methyllycaconitine (MLA) is reported. The analogues were synthesised via a one-pot cyclisation using ethyl alpha-(bromomethyl) acrylate, (R)-1-phenylethanamine and cyclohexanone to form chiral octahydroquinolines which can be selectively hydrogenated to form the 3-substituted-decahydroquinolines with the same stereochemistry found in MLA. The amine and ketone components in the one-pot reaction can also be altered to provide access to structurally related heterocycles.

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  • Synthesis and structural insight into ESX-1 Substrate Protein C, an immunodominant Mycobacterium tuberculosis-secreted antigen

    Son, Soo; Harris, Paul; Squire, Christopher; Baker, Edward; Brimble, Margaret (2016-05)

    Journal article
    The University of Auckland Library

    Tuberculosis, the second leading cause of death from a single infectious agent, is recognized as a major threat to human health due to a lack of practicable vaccines against the disease and the widespread occurrence of drug resistance. With a pressing need for a novel protein target as a platform for new vaccine development, ESX-1 Substrate Protein C (EspC) was recently identified as a novel Mycobacterium tuberculosis-secreted antigen that is as immunodominant as the two specific immunodiagnostic T-cell antigens, CFP-10 and ESAT-6. Here, we present the first chemical total synthesis, folding conditions, and circular dichroism data of EspC.

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  • Chemical synthesis of ??-secretase activating protein using pseudoglutamines as ligation sites

    Harris, Paul; Squire, Christopher; Young, PG; Brimble, Margaret (2015-01)

    Journal article
    The University of Auckland Library

    The chemical synthesis of analogue of a novel ??-secretase activating protein, which may play a pivotal role in the formation of amyloid peptides, the precursor to Alzheimer's disease, is described. The linear polypeptide sequence, consisting of 121 amino acids was assembled from four unprotected peptide building blocks using a convergent ligation-based synthesis. A strategic mutation of three glutamine residues to cysteine enabled the ligations, and the cysteines were subsequently converted to pseudoglutamines, to mimic the native glutamine. The full length unfolded protein was obtained in milligram amounts and was demonstrated to be homogeneous by liquid chromatography and mass spectrometry.

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  • Total chemical synthesis of an Orf virus protein, ORFV002, an inhibitor of the master gene regulator NF-??B

    Son, Soo; Harris, Paul; Squire, Christopher; Baker, Edward; Kent, SBH; Brimble, Margaret (2014-03)

    Journal article
    The University of Auckland Library

    ORFV002 is a novel orf viral protein (117 Aa) that inhibits nuclear events through the regulation of the transcriptional activity of NF-??B, a master regulator of human gene expression (Diel et al., J Virol 2011, 85, 264???275). It is identified as the first nuclear inhibitor of NF-??B produced by orf virus (ORFV) and no homologues in other genera of the Chordopoxvirinae subfamily have been reported to date (Diel et al., J Virol 2011, 85, 264???275). Our molecular structure predictions suggest that ORFV002 may mimic part of I??B, an inhibitor and natural human partner of NF-??B. Recent advances in total chemical synthesis of proteins have provided solutions in overcoming challenges of current recombinant methods of protein isolation for structure elucidation. Aided by Boc solid phase peptide synthesis and native chemical ligation, ORFV002 was successfully synthesized in multimilligram amounts in good yield and high purity.

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