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  • 1.
    Assarsson, A.
    et al.
    Lund University.
    Nasir, I.
    Lund University.
    Lundqvist, M.
    Lund University.
    Cabaleiro-Lago, Celia
    Lund Univeristy.
    Kinetic and thermodynamic study of the interactions between human carbonic anhydrase variants and polystyrene nanoparticles of different size2016In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 42, p. 35868-35874Article in journal (Refereed)
    Abstract [en]

    The activity and adsorption of three variants of human carbonic anhydrase (HCA) with similar topology but variation in charge and stability were studied in the presence of carboxyl-modified polystyrene nanoparticles of different sizes ranging from 25 nm to 114 nm. The balance of forces driving the adsorption of carbonic anhydrase variants is affected by the physicochemical properties of the protein and the nanoparticle size. All enzymes are totally inhibited upon adsorption due to the transition towards a molten globule like state that lacks enzymatic activity. The size of the particle affects the adsorption of human carbonic anhydrase I and N-terminal truncated human carbonic anhydrase II. Investigations on pH effects indicate that the size of the particle modulates the lateral interactions at the protein layer for these particular variants whose adsorption is mainly driven by electrostatic forces. A third variant, human carbonic anhydrase II, instead shows no strong influence of nanoparticle size which supports an adsorption process mainly driven by the hydrophobic effect.

  • 2.
    Assarsson, Anna
    et al.
    Lund University.
    Hellstrand, Erik
    Lund University.
    Cabaleiro-Lago, Celia
    Lund University.
    Linse, Sara
    Lund University.
    Charge dependent retardation of amyloid β aggregation by hydrophilic proteins2014In: ACS Chemical Neuroscience, ISSN 1948-7193, E-ISSN 1948-7193, Vol. 5, no 4, p. 266-74Article in journal (Refereed)
    Abstract [en]

    The aggregation of amyloid β peptides (Aβ) into amyloid fibrils is implicated in the pathology of Alzheimer's disease. In light of the increasing number of proteins reported to retard Aβ fibril formation, we investigated the influence of small hydrophilic model proteins of different charge on Aβ aggregation kinetics and their interaction with Aβ. We followed the amyloid fibril formation of Aβ40 and Aβ42 using thioflavin T fluorescence in the presence of six charge variants of calbindin D9k and single-chain monellin. The formation of fibrils was verified with transmission electron microscopy. We observe retardation of the aggregation process from proteins with net charge +8, +2, -2, and -4, whereas no effect is observed for proteins with net charge of -6 and -8. The single-chain monellin mutant with the highest net charge, scMN+8, has the largest retarding effect on the amyloid fibril formation process, which is noticeably delayed at as low as a 0.01:1 scMN+8 to Aβ40 molar ratio. scMN+8 is also the mutant with the fastest association to Aβ40 as detected by surface plasmon resonance, although all retarding variants of calbindin D9k and single-chain monellin bind to Aβ40.

  • 3.
    Assarsson, Anna
    et al.
    Lund University.
    Linse, Sara
    Lund University.
    Cabaleiro-Lago, Celia
    Lund University.
    Effects of polyamino acids and polyelectrolytes on amyloid β fibril formation2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 29, p. 8812-8Article in journal (Refereed)
    Abstract [en]

    The fibril formation of the neurodegenerative peptide amyloid β (Aβ42) is sensitive to solution conditions, and several proteins and peptides have been found to retard the process. Aβ42 fibril formation was followed with ThT fluorescence in the presence of polyamino acids (poly-glutamic acid, poly-lysine, and poly-threonine) and other polymers (poly(acrylic acid), poly(ethylenimine), and poly(diallyldimethylammonium chloride). An accelerating effect on the Aβ42 aggregation process is observed from all positively charged polymers, while no effect is seen from the negative or neutral polymers. The accelerating effect is dependent on the concentration of positive polymer in a highly reproducible manner. Acceleration is observed from a 1:500 polymer to Aβ42 weight ratio and up. Polyamino acids and the other polymers exert quantitatively the same effect at the same concentrations based on weight. Fibrils are formed in all cases as verified by transmission electron microscopy. The concentrations of polymers required for acceleration are too low to affect the Aβ42 aggregation process through increased ionic strength or molecular crowding effects. Instead, the acceleration seems to arise from the locally increased Aβ42 concentration near the polymers, which favors association and affects the electrostatic environment of the peptide.

  • 4.
    Assarsson, Anna
    et al.
    Lund University.
    Pastoriza-Santos, Isabel
    Spain.
    Cabaleiro-Lago, Celia
    Lund University.
    Inactivation and adsorption of human carbonic anhydrase II by nanoparticles2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 31, p. 9448-56Article in journal (Refereed)
    Abstract [en]

    The enzymatic activity of human carbonic anhydrase II (HCAII) was studied in the presence of nanoparticles of different nature and charge. Negatively charged nanoparticles inhibit HCAII whereas no effect is seen for positively charged particles. The kinetic effects were correlated with the strength of binding of the enzyme to the particle surface as measured by ITC and adsorption assays. Moreover, conformational changes upon adsorption were observed by circular dichroism. The main initial driving force for the adsorption of HCAII to nanoparticles is of electrostatic nature whereas the hydrophobic effect is not strong enough to drive the initial binding. This is corroborated by the fact that HCAII do not adsorb on positively charged hydrophobic polystyrene nanoparticles. Furthermore, the dehydration of the particle and protein surface seems to play an important role in the inactivation of HCAII by carboxyl-modified polystyrene nanoparticles. On the other hand, the inactivation by unmodified polystyrene nanoparticles is mainly driven by intramolecular interactions established between the protein and the nanoparticle surface upon conformational changes in the protein.

  • 5.
    Cabaleiro-Lago, Celia
    et al.
    Irland.
    Quinlan-Pluck, Fiona
    Irland.
    Lynch, Iseult
    Irland.
    Dawson, Kenneth A
    Irland.
    Linse, Sara
    Lund University.
    Dual effect of amino modified polystyrene nanoparticles on amyloid β protein fibrillation2010In: ACS Chemical Neuroscience, ISSN 1948-7193, E-ISSN 1948-7193, Vol. 1, no 4, p. 279-87Article in journal (Refereed)
    Abstract [en]

    The fibrillation kinetics of the amyloid β peptide is analyzed in presence of cationic polystyrene nanoparticles of different size. The results highlight the importance of the ratio between the peptide and particle concentration. Depending on the specific ratio, the kinetic effects vary from acceleration of the fibrillation process by reducing the lag phase at low particle surface area in solution to inhibition of the fibrillation process at high particle surface area. The kinetic behavior can be explained if we assume a balance between two different pathways: first fibrillation of free monomer in solution and second nucleation and fibrillation promoted at the particle surface. The overall rate of fibrillation will depend on the interplay between these two pathways, and the predominance of one mechanism over the other will be determined by the relative equilibrium and rate constants.

  • 6.
    Cabaleiro-Lago, Celia
    et al.
    Irland.
    Quinlan-Pluck, Fiona
    Irland.
    Lynch, Iseult
    Irland.
    Lindman, Stina
    Lund University.
    Minogue, Aedin M
    Irland.
    Thulin, Eva
    Lund University.
    Walsh, Dominic M
    Irland.
    Dawson, Kenneth A
    Irland.
    Linse, Sara
    Lund University.
    Inhibition of amyloid beta protein fibrillation by polymeric nanoparticles2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 46, p. 15437-43Article in journal (Refereed)
    Abstract [en]

    Copolymeric NiPAM:BAM nanoparticles of varying hydrophobicity were found to retard fibrillation of the Alzheimer's disease-associated amyloid beta protein (Abeta). We found that these nanoparticles affect mainly the nucleation step of Abeta fibrillation. The elongation step is largely unaffected by the particles, and once the Abeta is nucleated, the fibrillation process occurs with the same rate as in the absence of nanoparticles. The extension of the lag phase for fibrillation of Abeta is strongly dependent on both the amount and surface character of the nanoparticles. Surface plasmon resonance studies show that Abeta binds to the nanoparticles and provide rate and equilibrium constants for the interaction. Numerical analysis of the kinetic data for fibrillation suggests that binding of monomeric Abeta and prefibrillar oligomers to the nanoparticles prevents fibrillation. Moreover, we find that fibrillation of Abeta initiated in the absence of nanoparticles can be reversed by addition of nanoparticles up to a particular time point before mature fibrils appear.

  • 7.
    Lundqvist, Martin
    et al.
    Lund University.
    Cabaleiro-Lago, Celia
    Lund University.
    Buffer formulation affects the interaction between lysozyme and polymeric nanoparticles2017In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 504, p. 78-85Article in journal (Refereed)
    Abstract [en]

    The effect of the buffer formulation in terms of buffer identity and ionic strength on the interaction between chicken egg lysozyme and carboxyl-modified polystyrene nanoparticles has been systematically studied. The time evolution of the fluorescence of a reporter molecule shows that lysozyme interacts with the nanoparticles in all the studied conditions. The interaction results in changes in protein conformation and decrease of the colloidal stability of nanoparticles. In absence of a background salt the rate of adsorption is affected mainly by the ionic strength of the buffer solution, although, specific buffer effects may contribute to a certain extent. The identity of the different buffer components does not significantly alter the dynamics of the process in presence of salt at constant ionic strength. However, an increase of ionic strength leads to slower processes indicating that the adsorption is affected by the presence of increasing number of ions in solution.

  • 8.
    Nasir, Irem
    et al.
    Lund University.
    Fatih, Warda
    Upper 2nd school, Klippan, Sweden.
    Svensson, Anja
    Upper 2nd school, Klippan, Sweden.
    Radu, Dennis
    Upper 2nd school, Klippan, Sweden.
    Linse, Sara
    Lund University.
    Cabaleiro-Lago, Celia
    Lund University.
    Lundqvist, Martin
    Lund University.
    High throughput screening method to explore protein interactions with nanoparticles2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 8Article in journal (Refereed)
    Abstract [en]

    The interactions of biological macromolecules with nanoparticles underlie a wide variety of current and future applications in the fields of biotechnology, medicine and bioremediation. The same interactions are also responsible for mediating potential biohazards of nanomaterials. Some applications require that proteins adsorb to the nanomaterial and that the protein resists or undergoes structural rearrangements. This article presents a screening method for detecting nanoparticle-protein partners and conformational changes on time scales ranging from milliseconds to days. Mobile fluorophores are used as reporters to study the interaction between proteins and nanoparticles in a high-throughput manner in multi-well format. Furthermore, the screening method may reveal changes in colloidal stability of nanomaterials depending on the physicochemical conditions.

  • 9.
    Nasir, Irem
    et al.
    Lund University.
    Linse, Sara
    Lund University.
    Cabaleiro-Lago, Celia
    Lund University.
    Fluorescent filter-trap assay for amyloid fibril formation kinetics in complex solutions2015In: ACS Chemical Neuroscience, ISSN 1948-7193, E-ISSN 1948-7193, Vol. 6, no 8, p. 1436-44Article in journal (Refereed)
    Abstract [en]

    Amyloid fibrils are the most distinct components of the plaques associated with various neurodegenerative diseases. Kinetic studies of amyloid fibril formation shed light on the microscopic mechanisms that underlie this process as well as the contributions of internal and external factors to the interplay between different mechanistic steps. Thioflavin T is a widely used noncovalent fluorescent probe for monitoring amyloid fibril formation; however, it may suffer from limitations due to the unspecific interactions between the dye and the additives. Here, we present the results of a filter-trap assay combined with the detection of fluorescently labeled amyloid β (Aβ) peptide. The filter-trap assay separates formed aggregates based on size, and the fluorescent label attached to Aβ allows for their detection. The times of half completion of the process (t1/2) obtained by the filter-trap assay are comparable to values from the ThT assay. High concentrations of human serum albumin (HSA) and carboxyl-modified polystyrene nanoparticles lead to an elevated ThT signal, masking a possible fibril formation event. The filter-trap assay allows fibril formation to be studied in the presence of those substances and shows that Aβ fibril formation is kinetically inhibited by HSA and that the amount of fibrils formed are reduced. In contrast, nanoparticles exhibit a dual-behavior governed by their concentration.

  • 10.
    Nasir, Irem
    et al.
    Lund University.
    Lundqvist, Martin
    Lund University.
    Cabaleiro-Lago, Celia
    Lund University.
    Size and surface chemistry of nanoparticles lead to a variant behavior in the unfolding dynamics of human carbonic anhydrase2015In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 7, no 41, p. 17504-15Article in journal (Refereed)
    Abstract [en]

    The adsorption induced conformational changes of human carbonic anhydrase I (HCAi) and pseudo wild type human carbonic anhydrase II truncated at the 17th residue at the N-terminus (trHCAii) were studied in presence of nanoparticles of different sizes and polarities. Isothermal titration calorimetry (ITC) studies showed that the binding to apolar surfaces is affected by the nanoparticle size in combination with the inherent protein stability. 8-Anilino-1-naphthalenesulfonic acid (ANS) fluorescence revealed that HCAs adsorb to both hydrophilic and hydrophobic surfaces, however the dynamics of the unfolding at the nanoparticle surfaces drastically vary with the polarity. The size of the nanoparticles has opposite effects depending on the polarity of the nanoparticle surface. The apolar nanoparticles induce seconds timescale structural rearrangements whereas polar nanoparticles induce hours timescale structural rearrangements on the same charged HCA variant. Here, a simple model is proposed where the difference in the timescales of adsorption is correlated with the energy barriers for initial docking and structural rearrangements which are firmly regulated by the surface polarity. Near-UV circular dichorism (CD) further supports that both protein variants undergo structural rearrangements at the nanoparticle surfaces regardless of being "hard" or "soft". However, the conformational changes induced by the apolar surfaces differ for each HCA isoform and diverge from the previously reported effect of silica nanoparticles.

  • 11.
    Sanagavarapu, Kalyani
    et al.
    Lund University.
    Nüske, Elisabeth
    Germany.
    Nasir, Irem
    USA.
    Meisl, Georg
    England.
    Immink, Jasper N
    Lund University.
    Sormanni, Pietro
    England.
    Vendruscolo, Michele
    England.
    Knowles, Tuomas P J
    England.
    Malmendal, Anders
    Lund University.
    Cabaleiro-Lago, Celia
    Kristianstad University, Faculty of Natural Science, Avdelningen för miljö- och biovetenskap. Kristianstad University, Faculty of Natural Science, Research environment Man & Biosphere Health (MABH). Lund University.
    Linse, Sara
    Lund University.
    A method of predicting the in vitro fibril formation propensity of Aβ40 mutants based on their inclusion body levels in E. coli2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, no 1Article in journal (Refereed)
    Abstract [en]

    Overexpression of recombinant proteins in bacteria may lead to their aggregation and deposition in inclusion bodies. Since the conformational properties of proteins in inclusion bodies exhibit many of the characteristics typical of amyloid fibrils. Based on these findings, we hypothesize that the rate at which proteins form amyloid fibrils may be predicted from their propensity to form inclusion bodies. To establish a method based on this concept, we first measured by SDS-PAGE and confocal microscopy the level of inclusion bodies in E. coli cells overexpressing the 40-residue amyloid-beta peptide, Aβ40, wild-type and 24 charge mutants. We then compared these results with a number of existing computational aggregation propensity predictors as well as the rates of aggregation measured in vitro for selected mutants. Our results show a strong correlation between the level of inclusion body formation and aggregation propensity, thus demonstrating the power of this approach and its value in identifying factors modulating aggregation kinetics.

  • 12.
    Szczepankiewicz, Olga
    et al.
    Lund University.
    Cabaleiro-Lago, Celia
    Lund University.
    Tartaglia, Gian Gaetano
    England.
    Vendruscolo, Michele
    England.
    Hunter, Thérèse
    Malta.
    Hunter, Gary J
    Malta.
    Nilsson, Hanna
    Lund University.
    Thulin, Eva
    Lund University.
    Linse, Sara
    Lund University.
    Interactions in the native state of monellin, which play a protective role against aggregation2011In: Molecular Biosystems, ISSN 1742-206X, E-ISSN 1742-2051, Vol. 7, no 2, p. 521-32Article in journal (Refereed)
    Abstract [en]

    A series of recent studies have provided initial evidence about the role of specific intra-molecular interactions in maintaining proteins in their soluble state and in protecting them from aggregation. Here we show that the amino acid sequence of the protein monellin contains two aggregation-prone regions that are prevented from initiating aggregation by multiple non-covalent interactions that favor their burial within the folded state of the protein. By investigating the behavior of single-chain monellin and a series of five of its mutational variants using a variety of biochemical, biophysical and computational techniques, we found that weakening of the non-covalent interaction that stabilizes the native state of the protein leads to an enhanced aggregation propensity. The lag time for fibrillation was found to correlate with the apparent midpoint of thermal denaturation for the series of mutational variants, thus showing that a reduced thermal stability is associated with an increased aggregation tendency. We rationalize these findings by showing that the increase in the aggregation propensity upon mutation can be predicted in a quantitative manner through the increase in the exposure to solvent of the amyloidogenic regions of the sequence caused by the destabilization of the native state. Our findings, which are further discussed in terms of the structure of monellin and the perturbation by the amino acid substitutions of the contact surface between the two subdomains that compose the folded state of monellin, provide a detailed description of the specific intra-molecular interactions that prevent aggregation by stabilizing the native state of a protein.

  • 13.
    Tavahodi, Mojtaba
    et al.
    Iran.
    Schulz, Christopher
    Lund University.
    Assarsson, Anna
    Lund University.
    Ortiz, Roberto
    Lund University.
    Ludwig, Roland
    Austria.
    Cabaleiro-Lago, Celia
    Lund University.
    Haghighi, Behzad
    Iran.
    Gorton, Lo
    Lund University.
    Interaction of polymer-coated gold nanoparticles with cellobiose dehydrogenase: the role of surface charges2018In: Journal of Electroanalytical Chemistry, ISSN 1572-6657, Vol. 819, p. 226-233Article in journal (Refereed)
    Abstract [en]

    Studying the interaction of functional proteins such as enzymes and nanoparticles (NPs) includes the important topic of investigating any possible changes in stability and function of enzymes in nanostructured environments. The effects of NPs on the enzyme activity and stability are governed by their physical and chemical properties such as structure, shape, size, surface chemistry and their surface charges. In this study, the influence of negatively and positively charged AuNPs are investigated on the activity of immobilized Myriococcum thermophilum cellobiose dehydrogenase (MtCDH) and its electron transfer rate with graphite electrodes modified with positively and negatively AuNPs. The MtCDH modified graphite electrode premodified with positively charged AuNPs showed an alkaline shift in the pH of maximum activity from pH5.5 to 8. No change in the pH of maximum activity was observed when MtCDH graphite electrodes were premodified with negatively charged AuNPs. The results clearly demonstrated the effect of surface charge of AuNPs on the activity of the enzyme. The catalytic current density and the KMapp value for MtCDH graphite electrode premodified with positively charged AuNPs were enhanced with up to 66 and 8 times, respectively. Two spectroscopic assays were also performed in solution to investigate the influence of the presence of positively or negatively charged AuNPs on the activity of MtCDH in homogeneous solution. The results clearly demonstrated that not only the rate of the heterogeneous electron transfer between the immobilized MtCDH and the electrode but also the rate of the homogeneous electron transfer between soluble MtCDH and the acceptor was highly dependent on the type of surface charge of the AuNPs.

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