Pilot-scale study of biomethanation in biological trickle bed reactors converting impure CO2 from a Full-scale biogas plant.

Research within biological methanation has been a great development using biotrickling filters (BTF), as a power-to-x solution, but research within up scaling is missing. This study investigates the commercial potential of biomethanation in BTF by operating two 1 m3 reactors which was implemented into a full-scale biogas plant. Several areas were investigated, such as enrichment and start-up, long-term steady state operation, serial operation, and intermittent feed. A methane productivity of [Formula: see text] with a product gas of 95.7 % CH4 was obtained for parallel operation, whereas during serial operation a methane productivity of [Formula: see text] at 97.4 % CH4 was achieved. The flexibility of the biomethanation was demonstrated with unintentional loss of H2 feed in periods of 12 to 72 h, where initial performance was regained within 6 to 12 h. The results from this study demonstrate the potential for commercial use of biomethanation in BTF for future Power-to-X solutions.

Enzyme affinity to cell types in wheat straw (Triticum aestivum L.) before and after hydrothermal pretreatment.

BACKGROUND: Wheat straw used for bioethanol production varies in enzymatic digestibility according to chemical structure and composition of cell walls and tissues. In this work, the two biologically different wheat straw organs, leaves and stems, are described together with the effects of hydrothermal pretreatment on chemical composition, tissue structure, enzyme adhesion and digestion. To highlight the importance of inherent cell wall characteristics and the diverse effects of mechanical disruption and biochemical degradation, separate leaves and stems were pretreated on lab-scale and their tissue structures maintained mostly intact for image analysis. Finally, samples were enzymatically hydrolysed to correlate digestibility to chemical composition, removal of polymers, tissue composition and disruption, particle size and enzyme adhesion as a result of pretreatment and wax removal. For comparison, industrially pretreated wheat straw from Inbicon A/S was included in all the experiments. RESULTS: Within the same range of pretreatment severities, industrial pretreatment resulted in most hemicellulose and epicuticular wax/cutin removal compared to lab-scale pretreated leaves and stems but also in most re-deposition of lignin on the surface. Tissues were furthermore degraded from tissues into individual cells while lab-scale pretreated samples were structurally almost intact. In both raw leaves and stems, endoglucanase and exoglucanase adhered most to parenchyma cells; after pretreatment, to epidermal cells in all the samples. Despite heavy tissue disruption, industrially pretreated samples were not as susceptible to enzymatic digestion as lab-scale pretreated leaves while lab-scale pretreated stems were the least digestible. CONCLUSIONS: Despite preferential enzyme adhesion to epidermal cells after hydrothermal pretreatment, our results suggest that the single most important factor determining wheat straw digestibility is the fraction of parenchyma cells rather than effective tissue disruption.

Modulation of fibrillation of hIAPP core fragments by chemical modification of the peptide backbone.

The well-ordered cross ß-strand structure found in amyloid aggregates is stabilized by many different side chain interactions, including hydrophobic interactions, electrostatic charge and the intrinsic propensity to form ß-sheet structures. In addition to the side chains, backbone interactions are important because of the regular hydrogen-bonding pattern. ß-Sheet breaking peptide analogs, such as those formed by N-methylation, interfere with the repetitive hydrogen bonding pattern of peptide strands. Here we test backbone contributions to fibril stability using analogs of the 6-10 residue fibril core of human islet amyloid polypeptide, a 37 amino acid peptide involved in the pathogenesis of type II diabetes. The Phe-Gly peptide bond has been replaced by a hydroxyethylene or a ketomethylene group and the nitrogen-atom has been methylated. In addition, we have prepared peptoids where the side chain is transferred to the nitrogen atom. The backbone turns out to be extremely sensitive to substitution, since only the minimally perturbed ketomethylene analog (where only one of the -NH- groups has been replaced by -CH(2)-) can elongate wildtype fibrils but cannot fibrillate on its own. The resulting fibrils displayed differences in both secondary structure and overall morphology. No analog could inhibit the fibrillation of the parent peptide, suggesting an inability to bind to existing fibril surfaces. In contrast, side chain mutations that left the backbone intact but increased backbone flexibility or removed stabilizing side-chain interactions had very small effect on fibrillation kinetics. We conclude that fibrillation is very sensitive to even small modifications of the peptide backbone.

A thermodynamic analysis of fibrillar polymorphism.

We explore the thermodynamic properties of three different fibrils of the peptide hormone glucagon, formed under different salt conditions (glycine, sulfate and NaCl, respectively), and differing considerably in compactness. The three fibrils display a large variation in the specific heat capacity DeltaC(p) determined by isothermal titration calorimetry. Sulfate fibrils show a negative DeltaC(p) expected from a folding reaction, while the DeltaC(p) for glycine fibrils is essentially zero. NaCl fibrils, which are less stable than the other fibrils, have a large and positive C(p). The predicted change in solvent accessible area is not a useful predictor of fibrillar DeltaC(p) unlike the case for globular proteins. We speculate that strong backbone interactions may lead to the unfavorable burial of polar side residues, water and/or charged groups which all can have major influence on the change in C(p). These results highlight differences in the driving forces of native folding and fibril formation.

Crystallographic analysis reveals a unique lidocaine binding site on human serum albumin.

Human serum albumin (HSA), the major protein component in blood plasma and in extravascular spaces, is known to participate in the binding and transport of a variety of endogenous and exogenous organic compounds with anionic or electronegative features. We here report on the 3.3A resolution crystal structure of HSA complexed with the cationic, and widely used, anesthetic lidocaine. We find that lidocaine and HSA co-crystallise as a dimer in the unusual space group I4(1). The dimer consists of one HSA molecule without ligand and one HSA molecule with a single, bound lidocaine. HSA is a heart-shaped protein composed of three homologous helical domains (I-III), which can be subdivided into two subdomains (A and B), and lidocaine binds to a unique site formed by residues from subdomain IB facing the central, interdomain crevice. In the crystal, binding seems to introduce only local conformational changes in the protein. According to intrinsic fluorescence experiments with aqueous HSA binding results in widespread conformational changes involving Trp214 in subdomain IIA. Results obtained with equilibrium dialysis and isothermal titration calorimetry show that lidocaine binding is of a low affinity and occurs at one discrete binding site in accordance with the X-ray data. Another crystal form of ligand-free HSA obtained in the presence of ammonium sulphate was determined at 2.3A resolution revealing a sulphate ion accepting cavity at the surface of subdomain IIIA. The present results contribute to a further characterisation of the exceptional binding properties of HSA.

The role of protonation in protein fibrillation.

Many proteins fibrillate at low pH despite a high population of charged side chains. Therefore exchange of protons between the fibrillating peptide and its surroundings may play an important role in fibrillation. Here, we use isothermal titration calorimetry to measure exchange of protons between buffer and the peptide hormone glucagon during fibrillation. Glucagon absorbs or releases protons to an extent which allows it to attain a net charge of zero in the fibrillar state, both at acidic and basic pH. Similar results are obtained for lysozyme. This suggests that side chain pK(a) values change dramatically in the fibrillar state.

Unique identification of supramolecular structures in amyloid fibrils by solid-state NMR spectroscopy.

The fibril structure formed by the amyloidogenic fragment SNNFGAILSS of the human islet amyloid polypeptide (hIAPP) is determined with 0.52 A resolution. Symmetry information contained in the easily obtainable resonance assignments from solid-state NMR spectra (see picture), along with long-range constraints, can be applied to uniquely identify the supramolecular organization of fibrils.