Lytic polysaccharide monooxygenase (LPMO) supports biomass hydrolysis by increasing saccharification efficiency and rate. Recent studies demonstrate that H
O
rather than O
is the cosubstrate of the ...LPMO-catalyzed depolymerization of polysaccharides. Some studies have questioned the physiological relevance of the H
O
-based mechanism for plant cell wall degradation. This study reports the localized and time-resolved determination of LPMO activity on poplar wood cell walls by measuring the H
O
concentration in their vicinity with a piezo-controlled H
O
microsensor. The investigated Neurospora crassa LPMO binds to the inner cell wall layer and consumes enzymatically generated H
O
. The results point towards a high catalytic efficiency of LPMO at a low H
O
concentration that auxiliary oxidoreductases in fungal secretomes can easily generate. Measurements with a glucose microbiosensor additionally demonstrate that LPMO promotes cellobiohydrolase activity on wood cell walls and plays a synergistic role in the fungal extracellular catabolism and in industrial biomass degradation.
Lignocelluloytic enzymes are industrially applied as biocatalysts for the deconstruction of recalcitrant plant biomass. To study their biocatalytic and physiological function, the assessment of their ...binding behavior and spatial distribution on lignocellulosic material is a crucial prerequisite. In this study, selected hydrolases and oxidoreductases from the white rot fungus
were localized on model substrates as well as poplar wood by confocal laser scanning microscopy. Two different detection approaches were investigated: direct tagging of the enzymes and tagging specific antibodies generated against the enzymes. Site-directed mutagenesis was employed to introduce a single surface-exposed cysteine residue for the maleimide site-specific conjugation. Specific polyclonal antibodies were produced against the enzymes and were labeled using N-hydroxysuccinimide (NHS) ester as a cross-linker. Both methods allowed the visualization of cell wall-bound enzymes but showed slightly different fluorescent yields. Using native poplar thin sections, we identified the innermost secondary cell wall layer as the preferential attack point for cellulose-degrading enzymes. Alkali pretreatment resulted in a partial delignification and promoted substrate accessibility and enzyme binding. The methods presented in this study are suitable for the visualization of enzymes during catalytic biomass degradation and can be further exploited for interaction studies of lignocellulolytic enzymes in biorefineries.
Cellobiose dehydrogenase (CDH) is an extracellular fungal oxidoreductase with multiple functions in plant biomass degradation. Its primary function as an auxiliary enzyme of lytic polysaccharide ...monooxygenase (LPMO) facilitates the efficient depolymerization of cellulose, hemicelluloses and other carbohydrate-based polymers. The synergistic action of CDH and LPMO that supports biomass-degrading hydrolases holds significant promise to harness renewable resources for the production of biofuels, chemicals, and modified materials in an environmentally sustainable manner. While previous phylogenetic analyses have identified four distinct classes of CDHs, only class I and II have been biochemically characterized so far.
Following a comprehensive database search aimed at identifying CDH sequences belonging to the so far uncharacterized class III for subsequent expression and biochemical characterization, we have curated an extensive compilation of putative CDH amino acid sequences. A sequence similarity network analysis was used to cluster them into the four distinct CDH classes. A total of 1237 sequences encoding putative class III CDHs were extracted from the network and used for phylogenetic analyses. The obtained phylogenetic tree was used to guide the selection of 11 cdhIII genes for recombinant expression in Komagataella phaffii. A small-scale expression screening procedure identified a promising cdhIII gene originating from the plant pathogen Fusarium solani (FsCDH), which was selected for expression optimization by signal peptide shuffling and subsequent production in a 5-L bioreactor. The purified FsCDH exhibits a UV-Vis spectrum and enzymatic activity similar to other characterized CDH classes.
The successful production and functional characterization of FsCDH proved that class III CDHs are catalytical active enzymes resembling the key properties of class I and class II CDHs. A detailed biochemical characterization based on the established expression and purification strategy can provide new insights into the evolutionary process shaping CDHs and leading to their differentiation into the four distinct classes. The findings have the potential to broaden our understanding of the biocatalytic application of CDH and LPMO for the oxidative depolymerization of polysaccharides.
Cellobiose dehydrogenase from Phanerochaete chrysosporium (PcCDH) is a key enzyme in lignocellulose depolymerization, biosensors and biofuel cells. For these applications, it should retain important ...molecular and catalytic properties when recombinantly expressed. While homologous expression is time-consuming and the prokaryote Escherichia coli is not suitable for expression of the two-domain flavocytochrome, the yeast Pichia pastoris is hyperglycosylating the enzyme. Fungal expression hosts like Aspergillus niger and Trichoderma reesei were successfully used to express CDH from the ascomycete Corynascus thermophilus. This study describes the expression of basidiomycetes PcCDH in T. reesei (PcCDH
) and the detailed comparison of its molecular, catalytic and electrochemical properties in comparison with PcCDH expressed by P. chrysosporium and P. pastoris (PcCDH
).
PcCDH
was recombinantly produced with a yield of 600 U L
after 4 days, which is fast compared to the secretion of the enzyme by P. chrysosporium. PcCDH
and PcCDH were purified to homogeneity by two chromatographic steps. Both enzymes were comparatively characterized in terms of molecular and catalytic properties. The pH optima for electron acceptors are identical for PcCDH
and PcCDH. The determined FAD cofactor occupancy of 70% for PcCDH
is higher than for other recombinantly produced CDHs and its catalytic constants are in good accordance with those of PcCDH. Mass spectrometry showed high mannose-type N-glycans on PcCDH, but only single N-acetyl-D-glucosamine additions at the six potential N-glycosylation sites of PcCDH
, which indicates the presence of an endo-N-acetyl-β-D-glucosaminidase in the supernatant.
Heterologous production of PcCDH
is faster and the yield higher than secretion by P. chrysosporium. It also does not need a cellulose-based medium that impedes efficient production and purification of CDH by binding to the polysaccharide. The obtained high uniformity of PcCDH
glycoforms will be very useful to investigate electron transfer characteristics in biosensors and biofuel cells, which are depending on the spatial restrictions inflicted by high-mannose N-glycan trees. The determined catalytic and electrochemical properties of PcCDH
are very similar to those of PcCDH and the FAD cofactor occupancy is good, which advocates T. reesei as expression host for engineered PcCDH for biosensors and biofuel cells.
Future biorefineries are facing the challenge to separate and depolymerize biopolymers into their building blocks for the production of biofuels and basic molecules as chemical stock. Fungi have ...evolved lignocellulolytic enzymes to perform this task specifically and efficiently, but a detailed understanding of their heterogeneous reactions is a prerequisite for the optimization of large-scale enzymatic biomass degradation. Here, we investigate the binding of cellulolytic enzymes onto biopolymers by surface plasmon resonance (SPR) spectroscopy for the fast and precise characterization of enzyme adsorption processes. Using different sensor architectures, SPR probes modified with regenerated cellulose as well as with lignin films were prepared by spin-coating techniques. The modified SPR probes were analyzed by atomic force microscopy and static contact angle measurements to determine physical and surface molecular properties. SPR spectroscopy was used to study the activity and affinity of
Trichoderma reesei
cellobiohydrolase I (CBHI) glycoforms on the modified SPR probes. N-glycan removal led to no significant change in activity or cellulose binding, while a slightly higher tendency for non-productive binding to SPR probes modified with different lignin fractions was observed. The results suggest that the main role of the N-glycosylation in CBHI is not to prevent non-productive binding to lignin, but probably to increase its stability against proteolytic degradation. The work also demonstrates the suitability of SPR-based techniques for the characterization of the binding of lignocellulolytic enzymes to biomass-derived polymers.
Graphic abstract
The first lytic polysaccharide monooxygenase (LPMO) detected in the genome of the widespread ascomycete
(TamAA9A) has been successfully expressed in
and characterized. Molecular modeling of TamAA9A ...showed a structure similar to those from other AA9 LPMOs. Although fungal LPMOs belonging to the genera
or
have not been analyzed in terms of regioselectivity, phylogenetic analyses suggested C1/C4 oxidation which was confirmed by HPAEC. To ascertain the function of a C-terminal linker-like region present in the wild-type sequence of the LPMO, two variants of the wild-type enzyme, one without this sequence and one with an additional C-terminal carbohydrate binding domain (CBM), were designed. The three enzymes (native, without linker and chimeric variant with a CBM) were purified in two chromatographic steps and were thermostable and active in the presence of H
O
. The transition midpoint temperature of the wild-type LPMO (Tm = 67.7 °C) and its variant with only the catalytic domain (Tm = 67.6 °C) showed the highest thermostability, whereas the presence of a CBM reduced it (Tm = 57.8 °C) and indicates an adverse effect on the enzyme structure. Besides, the potential of the different
LPMO variants for their application in the saccharification of cellulosic and lignocellulosic materials was corroborated.
Refining of cellulose fibers is essential for reaching desired paper properties, yet highly energy demanding. Enzymes like endoglucanases (e.g. EndoC) are increasingly used to reduce energy ...consumption during pulp refining. However, prediction of the enzyme effect is still a major concern, considering the high variety of commercially available enzyme formulations, containing a range of different enzymes. In this study, synergisms of xylanases and β-glucosidases in combination with endoglucanases purified from enzyme formulations were studied and related to their refining performance. Size exclusion chromatography with multi-angle laser light scattering (SEC-MALLS) of carboxymethylcellulose revealed that a narrow size distribution and a high reduction in molecular weight are beneficial characteristics for refining. SEC-MALLS of hardwood pulp resulted in pronounced formation of low molecular weight fractions (log MW 4.3) for most efficient refining enzymes. Application of enzyme formulations and combinations of endoglucanase EndoC with β-glucosidase or xylanase using Fourier-transform infrared spectroscopy (FTIR) revealed synergistic effects that promoted degradation of amorphous parts of cellulose. Laboratory refining trials on hardwood pulp confirmed the increase in degree of refining and tensile index after addition of xylanase and β-glucosidase. Surface plasmon resonance (SPR) analysis resulted in strong binding of endoglucanases to regenerated cellulose, which correlated to refining performance.
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Cellobiose dehydrogenase in biofuel cells Scheiblbrandner, Stefan; Csarman, Florian; Ludwig, Roland
Current opinion in biotechnology,
02/2022, Volume:
73
Journal Article
Peer reviewed
Open access
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Enzymatic biofuel cells utilize oxidoreductases as highly specific and highly active electrocatalysts to convert a fuel and an oxidant even in complex biological matrices like ...hydrolysates or physiological fluids into electric energy. The hemoflavoenzyme cellobiose dehydrogenase is investigated as a versatile bioelectrocatalyst for the anode reaction of biofuel cells, because it is robust, converts a range of different carbohydrates, and can transfer electrons to the anode by direct electron transfer or via redox mediators. The versatility of cellobiose dehydrogenase has led to the development of various electrode modifications to create biofuel cells and biosupercapacitors that are capable to power small electronic devices like biosensors and connect them wireless to a receiver.
The interdomain electron transfer (IET) between the catalytic flavodehydrogenase domain and the electron-transferring cytochrome domain of cellobiose dehydrogenase (CDH) plays an essential role in ...biocatalysis, biosensors and biofuel cells, as well as in its natural function as an auxiliary enzyme of lytic polysaccharide monooxygenase. We investigated the mobility of the cytochrome and dehydrogenase domains of CDH, which is hypothesised to limit IET in solution by small angle X-ray scattering (SAXS). CDH from Myriococcum thermophilum (syn. Crassicarpon hotsonii, syn. Thermothelomyces myriococcoides) was probed by SAXS to study the CDH mobility at different pH and in the presence of divalent cations. By comparison of the experimental SAXS data, using pair-distance distribution functions and Kratky plots, we show an increase in CDH mobility at higher pH, indicating alterations of domain mobility. To further visualise CDH movement in solution, we performed SAXS-based multistate modelling. Glycan structures present on CDH partially masked the resulting SAXS shapes, we diminished these effects by deglycosylation and studied the effect of glycoforms by modelling. The modelling shows that with increasing pH, the cytochrome domain adopts a more flexible state with significant separation from the dehydrogenase domain. On the contrary, the presence of calcium ions decreases the mobility of the cytochrome domain. Experimental SAXS data, multistate modelling and previously reported kinetic data show how pH and divalent ions impact the closed state necessary for the IET governed by the movement of the CDH cytochrome domain.
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