| 1. |
- Guo, Boyang, et al.
(författare)
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Conformational Selection in Biocatalytic Plastic Degradation by PETase
- 2022
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 12:6, s. 3397-3409
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Tidskriftsartikel (refereegranskat)abstract
- Due to the steric effects imposed by bulky polymers, the formation of catalytically competent enzyme and substrate conformations is critical in the biodegradation of plastics. In poly(ethylene terephthalate) (PET), the backbone adopts different conformations, gauche and trans, coexisting to different extents in amorphous and crystalline regions. However, which conformation is susceptible to biodegradation and the extent of enzyme and substrate conformational changes required for expedient catalysis remain poorly understood. To overcome this obstacle, we utilized molecular dynamics simulations, docking, and enzyme engineering in concert with high-resolution microscopy imaging and solid-state nuclear magnetic resonance (NMR) to demonstrate the importance of conformational selection in biocatalytic plastic hydrolysis. Our results demonstrate how single-amino acid substitutions in Ideonella sakaiensis PETase can alter its conformational landscape, significantly affecting the relative abundance of productive ground-state structures ready to bind discrete substrate conformers. We experimentally show how an enzyme binds to plastic and provide a model for key residues involved in the recognition of gauche and trans conformations supported by in silico simulations. We demonstrate how enzyme engineering can be used to create a trans-selective variant, resulting in higher activity when combined with an all-trans PET-derived oligomeric substrate, stemming from both increased accessibility and conformational preference. Our work cements the importance of matching enzyme and substrate conformations in plastic hydrolysis, and we show that also the noncanonical trans conformation in PET is conducive for degradation. Understanding the contribution of enzyme and substrate conformations to biocatalytic plastic degradation could facilitate the generation of designer enzymes with increased performance.
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| 2. |
- Josefsson, Leila, et al.
(författare)
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Potato Protein Nanofibrils Produced from a Starch Industry Sidestream
- 2020
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Ingår i: ACS Sustainable Chemistry and Engineering. - : AMER CHEMICAL SOC. - 2168-0485. ; 8:2, s. 1058-1067
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Tidskriftsartikel (refereegranskat)abstract
- Protein nanofibrils have emerged as promising building blocks in functional bio/nanomaterials as well as in food products. We here demonstrate that nanofibrils with amyloid-like properties can be produced from potato protein isolate, a major sidestream from the starch industry. Methods for solubilization of potato proteins are evaluated, and a protocol for the assembly of protein nanofibrils is presented. Characterization of the nanofibrils shows that they are rich in beta-sheet structure and display the cross-beta X-ray fiber diffraction pattern, which is a hallmark of amyloid-like fibrils. Atomic force microscopy shows that the fibrils are ca. 4-5 nm in diameter with a nanoscale morphology that displays a high degree of curvature. Using mass spectrometry we identify four peptides that constitute the core building blocks of the nanofibrils and show that they originate from two different classes of proteins. The structural characteristics of these peptides are distinct from previously studied plant protein nanofibrils and thereby reveal new knowledge about the formation of protein nanostructures from agricultural resources.
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| 3. |
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| 4. |
- Proietti, Giampiero, et al.
(författare)
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Nickel Boride Catalyzed Reductions of Nitro Compounds and Azides : Nanocellulose-supported Catalysts in Tandem Reactions
- 2022
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Ingår i: Synthesis (Stuttgart). - : Georg Thieme Verlag KG. - 0039-7881 .- 1437-210X. ; 54:01, s. 133-146
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Tidskriftsartikel (refereegranskat)abstract
- Nickel boride catalyst prepared in situ from NiCl2 and sodium borohydride allowed, in the presence of an aqueous solution of TEMPO-oxidized nanocellulose (0.01 wt%), the reduction of a wide range of nitroarenes and aliphatic nitro compounds. Here we describe how the modified nanocellulose has a stabilizing effect on the catalyst that enables low loading of the nickel salt pre-catalyst. Ni-B prepared in situ from a methanolic solution was also used to develop a greener and facile reduction of azides, offering a substantially lowered catalyst loading with respect to reported methods in the literature. Both aromatic and aliphatic azides were reduced and the protocol is compatible with a one-pot Boc-protection of the obtained amine yielding the corresponding carbamates. Finally, bacterial crystalline nanocellulose was chosen as a support for the Ni-B catalyst to allow an easy recovery step of the catalyst and its recyclability for new reduction cycles.
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| 5. |
- Wei, Xin-Feng, et al.
(författare)
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Water-assisted extrusion of carbon fiber-reinforced wheat gluten for balanced mechanical properties
- 2022
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Ingår i: Industrial crops and products (Print). - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 180
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Tidskriftsartikel (refereegranskat)abstract
- Plasticizers turn brittle bio-based and biodegradable highly hydrophilic polymers into tough materials. Unfortunately, it also means that the material becomes softer and weaker. The concept of combining a plasticizer and reinforcing fibers was investigated here on a protein material (wheat gluten) plasticized with glycerol and reinforced with chopped carbon fibers. The carbon fibers showed good interfacial bonding with the gluten matrix and improved both tensile strength and Young's modulus of the material. The resulting composites also showed reduced elongation at break but still underwent ductile fracture under tension. Water-assisted extrusion, where water was used as a processing aid, was used to manufacture the composites and boost the reinforcement. Water addition significantly reduced the viscosity of the gluten dough and thus decreased fiber breakage during extrusion/compounding. The composites prepared with water-assisted extrusion had much longer fibers and consequently higher stiffness than those prepared without water. Apart from the balanced mechanical properties, the resulting composites showed reduced uptake of moisture (reduced moisture sensitivity) due to the waterimpermeable carbon fibers. Hence, a new extrusion method was presented for fiber-reinforced inherently viscous plant-based polymer composites, which enabled good mixing without critical fiber damage and thus improved fiber reinforcement.
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| 6. |
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| 7. |
- Ye, Xinchen, et al.
(författare)
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High-Temperature and Chemically Resistant Foams from Sustainable Nanostructured Protein
- 2021
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Ingår i: Advanced sustainable systems. - : Wiley. - 2366-7486. ; , s. 2100063-
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Tidskriftsartikel (refereegranskat)abstract
- Covalently crosslinked protein networks produced from whey protein nanofibrils (PNFs) are demonstrated to be sustainable high-performance foams that show chemical resistance and mechanical strength, stiffness, and toughness on harsh aging at 150 °C. The aged foams are able to retain their properties at 180 °C for as long as 24 h, far exceeding the properties of most classical petroleum-based thermoplastics. The foams are further developed into soft foams by the addition of glycerol as a plasticizer. The improvement in the mechanical performance of the foams with aging, which is equivalent to an increase by one order of magnitude in modulus and yield strength, is confirmed to be associated with (iso)peptide crosslinks. The results open the way for using protein-based foam materials in severe/corrosive environments such as filtration, thermal insulation, and fluid absorption. The protein foams produced are suggested as suitable alternatives to petroleum-based porous polymers.
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| 8. |
- Ye, Xinchen
(författare)
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Materials Based on Protein Nanofibrils
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Protein nanofibrils (PNFs) prepared from whey protein isolate (WPI) at low pH and elevated temperature were processed into materials, i.e. hydrogels, films, foams, and fibres, for different applications where they could potentially be sustainable alternatives to petroleum-based polymers. WPI was chosen as the starting material due to the high accessibility of whey as an industrial side-stream product from cheese manufacturing, and its ability to easily grow PNFs.PNFs grown in the presence of different metal ions were generally curved and short, and they formed hydrogels, in contrast to the straight ones fibrillated without metal ions. The effect of metal ions with different acidity was systematically studied with respect to fibrillation kinetics and gelation behaviour. The protein fibrillation was accelerated by the addition of metal ions. The strength of the hydrogel increased with increasing acidity of the metal ion at the same ion concentration, as long as the ion did not precipitate as hydroxide/oxide. Protein nanocomposite films were prepared by adding separately grown PNFs into a non-fibrillar protein matrix from the same WPI starting material. The glycerol-plasticized composite films obtained an increased elastic modulus and decreased strain at break with increasing content of PNFs. The produced PNF foams showed high-temperature resistance during aging at 150 °C for as long as one month (maximum testing time), far exceeding the properties of many petroleum-based thermoplastics. The aged foams were also able to retain their properties in different solutions that normally degrade/dissolve protein materials.PNFs were also organized into microfibres using a flow-focusing method. Genipin was added as a natural crosslinker to improve the mechanical properties of the obtained fibre. The crosslinked fibre (using only 2% genipin) obtained a significantly higher stiffness and strength at break as compared to the fibre assembled without genipin.
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| 9. |
- Ye, Xinchen, et al.
(författare)
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On the role of peptide hydrolysis for fibrillation kinetics and amyloid fibril morphology
- 2018
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Ingår i: RSC Advances. - : ROYAL SOC CHEMISTRY. - 2046-2069. ; 8:13, s. 6915-6924
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Tidskriftsartikel (refereegranskat)abstract
- Self-assembly of proteins into amyloid-like nanofibrils is not only a key event in several diseases, but such fibrils are also associated with intriguing biological function and constitute promising components for new biobased materials. The bovine whey protein beta-lactoglobulin has emerged as an important model protein for the development of such materials. We here report that peptide hydrolysis is the rate-determining step for fibrillation of beta-lactoglobulin in whey protein isolate. We also explore the observation that beta-lactoglobulin nanofibrils of distinct morphologies are obtained by simply changing the initial protein concentration. We find that the morphological switch is related to different nucleation mechanisms and that the two classes of nanofibrils are associated with variations of the peptide building blocks. Based on the results, we propose that the balance between protein concentration and the hydrolysis rate determines the structure of the formed nanofibrils.
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| 10. |
- Ye, Xinchen, et al.
(författare)
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Protein Nanofibrils and Their Hydrogel Formation with Metal Ions
- 2021
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 15:3, s. 5341-5354
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Tidskriftsartikel (refereegranskat)abstract
- Protein nanofibrils (PNFs) have been prepared by whey protein fibrillation at low pH and in the presence of different metal ions. The effect of the metal ions was systematically studied both in terms of PNF suspension gelation behavior and fibrillation kinetics. A high valence state and a small ionic radius (e.g., Sn4+) of the metal ion resulted in the formation of hydrogels already at a metal ion concentration of 30 mM, whereas an intermediate valence state and larger ionic radius (Co2+, Ni2+, Al3+) resulted in the hydrogel formation occurring at 60 mM. A concentration of 120 mM of Na+ was needed to form a PNF hydrogel, while lower concentrations showed liquid behaviors similar to the reference PNF solution where no metal ions had been introduced. The hydrogel mechanics were investigated at steady-state conditions after 24 h of incubation/gelation, revealing that more acidic (smaller and more charged) metal ions induced ca. 2 orders of magnitude higher storage modulus as compared to the less acidic metal ions (with smaller charge and larger radius) for the same concentration of metal ions. The viscoelastic nature of the hydrogels was attributed to the ability of the metal ions to coordinate water molecules in the vicinity of the PNFs. The presence of metal ions in the solutions during the growth of the PNFs typically resulted in curved fibrils, whereas an upper limit of the concentration existed when oxides/hydroxides were formed, and the hydrogels lost their gel properties due to phase separation. Thioflavin T (ThT) fluorescence was used to determine the rate of the fibrillation to form 50% of the total PNFs (t(1/2)), which decreased from 2.3 to ca. 0.5 h depending on the specific metal ions added.
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