Browsing by Author "Klumperman, Bert"

Now showing 1 - 7 of 7
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    Advancing membrane biology with poly(styrene-co-maleic acid)-based native nanodiscs
    (Elsevier, 2019) Overduin, Michael; Klumperman, Bert
    ENGLISH ABSTRACT: The elucidation of the structures and interactions of proteins and lipids in intact biological membranes remains largely uncharted territory. However, this information is crucial for understanding how organelles are assembled and how transmembrane machines transduce signals. The challenge of seeing how lipids and proteins engage each other in vivo remains difficult but is being aided by a group of amphipathic copolymers that spontaneously fragment native membranes into native nanodiscs. Poly(styrene-co-maleic acid) (SMA) copolymers have proven adept at converting membranes, cells and tissues directly into SMA lipid particles (SMALPs), allowing endogenous lipid: protein complexes to be prepared and analyzed. Unlike other amphipathic polymers such as amphipols, SMALP formation requires no conventional detergents, which typically strip lipid molecules from proteins and can destabilize multimers. A collaborative community of hundreds of investigators known as the SMALP network has emerged to develop and apply new technologies and identify new challenges and design potential solutions. In this contribution, we review recent practices and progress, focusing on novel SMA copolymers, modifications, alternatives and mechanisms. In addition, a brief overview will be provided, with reference to the further contributions to this special issue on the SMALP technology.
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    Coordinated autophagy modulation overcomes glioblastoma chemoresistance through disruption of mitochondrial bioenergetics
    (Nature Research, 2018-07-09) Kriel, Jurgen; Muller-Nedebock, Kristian; Maarman, Gerald; Mbizana, Siyasanga; Ojuka, Edward; Klumperman, Bert; Loos, Ben
    Glioblastoma Multiforme (GBM) is known to be one of the most malignant and aggressive forms of brain cancer due to its resistance to chemotherapy. Recently, GBM was found to not only utilise both oxidative phosphorylation (OXPHOS) and aerobic glycolysis, but also depend on the bulk protein degradation system known as macroautophagy to uphold proliferation. Although autophagy modulators hold great potential as adjuvants to chemotherapy, the degree of upregulation or inhibition necessary to achieve cell death sensitisation remains unknown. Therefore, this study aimed to determine the degree of autophagy modulation necessary to impair mitochondrial bioenergetics to the extent of promoting cell death onset. It was shown that coordinated upregulation of autophagy followed by its inhibition prior to chemotherapy decreased electron transfer system (ETS) and oxidative phosphorylation (OXPHOS) capacity, impaired mitochondrial fission and fusion dynamics and enhanced apoptotic cell death onset in terms of cleaved caspase 3 and cleaved PARP expression. Therefore, coordinated autophagy modulation may present a favourable avenue for improved chemotherapeutic intervention in the future.
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    Degradation of proteins and starch by combined immobilization of protease, α-amylase and β-galactosidase on a single electrospun nanofibrous membrane
    (MDPI, 2019-01-31) Cloete, William J.; Hayward, Stefan; Swart, Pieter; Klumperman, Bert
    Two commercially available enzymes, Dextrozyme (α-amylase) and Esperase (protease), were covalently immobilized on non-woven electrospun poly(styrene-co-maleic anhydride) nanofiber mats with partial retention of their catalytic activity. Immobilization was achieved for the enzymes on their own as well as in different combinations with an additional enzyme, β-galactosidase, on the same non-woven nanofiber mat. This experiment yielded a universal method for immobilizing different combinations of enzymes with nanofibrous mats containing maleic anhydride (MAnh) residues in the polymer backbone.
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    Facile route to targeted, biodegradable polymeric prodrugs for the delivery of combination therapy for Malaria
    (American Chemical Society, 2020-06) Fortuin, Lisa; Leshabane, Meta; Pfukwa, Rueben; Coertzen, Dina; Birkholtz, Lyn-Marie; Klumperman, Bert
    A facile synthetic methodology has been developed to prepare multifaceted polymeric prodrugs that are targeted, biodegradable, and nontoxic, and used for the delivery of combination therapy. This is the first instance of the delivery of the WHO recommended antimalarial combination of lumefantrine (LUM, drug 1) and artemether (AM, drug 2) via a polymeric prodrug. To achieve this, reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization of N-vinylpyrrolidone (NVP) was conducted using a hydroxy-functional RAFT agent, and the resulting polymer was used as the macroinitiator in the ring-opening polymerization (ROP) of α-allylvalerolactone (AVL) to synthesize the biodegradable block copolymer of poly(N-vinylpyrrolidone) and poly(α-allylvalerolactone) (PVP-b-PAVL). The ω-end thiol group of PVP was protected using 2,2′-pyridyldisulfide prior to the ROP, and was conveniently used to bioconjugate a peptidic targeting ligand. To attach LUM, the allyl groups of PVP-b-PAVL underwent oxidation to introduce carboxylic acid groups, which were then esterified with ethylene glycol vinyl ether. Finally, LUM was conjugated to the block copolymer via an acid-labile acetal linkage in a “click”-type reaction, and AM was entrapped within the hydrophobic core of the self-assembled aggregates to render biodegradable multidrug-loaded micelles with targeting ability for combination therapy.
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    NMR studies of radical polymerization processes
    (Stellenbosch : Stellenbosch University, 2012-12) Klumperman, Bert; Mallon, Peter E.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Examples of the use of NMR spectroscopy in the study of radical polymerization processes have been described. The studies presented have made a significant contribution to the understanding of the fundamental mechanistic processes in these polymerization systems. It is pointed out that NMR in conventional radical polymerization is of limited use due to the concurrent occurrence of all elementary reactions (initiation, propagation and termination). Conversely, for living radical polymerization, NMR has great value. In that case, the elementary reactions are somewhat more restricted to specific times of the polymerization process. This allows for example the detailed study of the early stages of chain growth in Reversible Addition-­‐Fragmentation Chain Transfer (RAFT) mediated polymerization. Two different studies are described. The first is related to the early stages of RAFT-­‐mediated polymerization. A process for which we coined the name initialization was studied via in situ 1H NMR spectroscopy. It is shown that in many cases, there is a selective reaction that converts the original RAFT agent into its single monomer adduct. A few different examples and their mechanistic interpretation are discussed. It is also shown that NMR spectroscopy can be a valuable tool for the assessment of a RAFT agent in conjunction with a specific monomer and polymerization conditions. In the second study, 15N NMR, 31P NMR and 1H NMR are used for two different types of experiments. The first is a conventional radical copolymerization in which the growing chains are trapped by a 15N labeled nitroxide to yield a stable product. In the second experiment, a similar copolymerization is conducted under nitroxide-­‐mediated conditions. The nitroxide of choice contains phosphorous, which enables the quantification of the terminal monomer in the dormant chains. Each of the experiments individually provides interesting information on conventional radical copolymerization and nitroxide-­‐mediated copolymerization, respectively. Combination of the experimental data reveals an interesting discrepancy in the ratio of terminal monomer units in active chains and dormant chains. Although not unexpected, this result is interesting and useful from a mechanistic as well as a synthetic point of view. In terms of future perspectives, it is expected that the advanced analytical techniques as described here will remain crucial in polymer science. Present developments in radical polymerization, such as investigations into monomer sequence control, rely on accurate knowledge of kinetic and mechanistic details of elementary reactions. It is expected that such detailed studies will be a main challenge for the next decade of polymer research.
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    Release of bacteriocins from nanofibers prepared with combinations of poly(D,L-lactide) (PDLLA) and poly(ethylene oxide) (PEO)
    (MDPI, 2011) Heunis, Tiaan; Bshena, Osama; Klumperman, Bert; Dicks, Leon Milner Theodore, 1961-
    Plantaricin 423, produced by Lactobacillus plantarum, and bacteriocin ST4SA produced by Enterococcus mundtii, were electrospun into nanofibers prepared from different combinations of poly(D,L-lactide) (PDLLA) and poly(ethylene oxide) (PEO) dissolved in N,N-dimethylformamide (DMF). Both peptides were released from the nanofibers with a high initial burst and retained 88% of their original antimicrobial activity at 37 °C. Nanofibers have the potential to serve as carrier matrix for bacteriocins and open a new field in developing controlled antimicrobial delivery systems for various applications.
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    Synthesis of novel glycopolymer brushes via a combination of RAFT-mediated polymerisation and ATRP
    (AOSIS Publishing, 2011-04) Fleet, Reda; Van Den Dungen, Eric T. A.; Klumperman, Bert
    ENGLISH ABSTRACT: Glycopolymers (synthetic sugar-containing polymers) have become increasingly attractive to polymer chemists because of their role as biomimetic analogues and their potential for commercial applications. Glycopolymers of different structures confer high hydrophilicity and water solubility and can therefore be used for specialised applications, such as artificial materials for a number of biological, pharmaceutical and biomedical uses. The synthesis and characterisation of a series of novel glycopolymer brushes, namely poly(2-(2- bromoisobutyryloxy) ethyl methacrylate)-g-poly(methyl 6-O-methacryloyl-α-D-glucoside) (P(BIEM)-g-P(6-O-MMAGIc)), poly(2-(2-bromoisobutyryloxy) ethyl methacrylate-co-methyl methacrylate)-g-poly(methyl 6-O-methacryloyl-α-D-glucoside) P(BIEM-co-MMA)-g-P(6- O-MMAGIc), poly(2-(2-bromoisobutyryloxy) ethyl methacrylate-b-methyl methacrylate)- g-poly(methyl 6-O-methacryloyl-α-D-glucoside) P(BIEM-b-MMA)-g-P(6-O-MMAGIc) and poly(4-vinylbenzyl chloride-alt-maleic anhydride)-g-poly(methyl 6-O-methacryloyl-α-Dglucoside) (P(Sd-alt-MAnh)-g-P(6-O-MMAGIc)) are described in this paper. Reversible addition-fragmentation chain transfer (RAFT)-mediated polymerisation was used to synthesise four well-defined atom transfer radical polymerisation (ATRP) macroinitiators (the backbone of the glycopolymer brushes). These ATRP macroinitiators were subsequently used in the ‘grafting from’ approach (in which side chains are grown from the backbone) to prepare high molar mass and low polydispersity index glycopolymer brushes with different grafting densities along the backbone. The number average molar mass of the glycopolymer brushes was determined using size exclusion chromatography with a multi-angle laser light scattering detector and further structural characterisation was conducted using 1H-nuclear magnetic resonance spectroscopy. The results confirmed that glycopolymer brushes were successfully synthesised via a combination of RAFT-mediated polymerisation and ATRP.