Pyranose dehydrogenases: Rare enzymes for electrochemistry and biocatalysis

Enzymatically Oxidized Carbohydrates As Dicarbonyl Biobased Cross-Linkers for Polyamines

Carbonyl cross-linkers are used to modify textiles and form resins, and are produced annually in megatonne volumes. Due to their toxicity toward the environment and human health, however, less harmful biobased alternatives are needed. This study introduces carbonyl groups to lactose and galactose using galactose oxidase from Fusarium graminearum (FgrGalOx) and pyranose dehydrogenase from Agaricus bisporus (AbPDH1) to produce four cross-linkers. Differential scanning calorimetry was used to compare cross-linker reactivity, most notably resulting in a 34 °C decrease in reaction peak temperature (72 °C) for FgrGalOx-oxidized galactose compared to unmodified galactose. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and proton nuclear magnetic resonance (1H NMR) spectroscopy were used to verify imine formation and amine and aldehyde depletion. Cross-linkers were shown to form gels when mixed with polyallylamine, with FgrGalOx-oxidized lactose forming gels more effectively than all other cross-linkers, including glutaraldehyde. Further development of carbohydrate cross-linker technologies could lead to their adoption in various applications, including in adhesives, resins, and textiles.

Whole genome sequence of Cryptosphaeria pullmanensis, an important pathogenic fungus potentially threatening crop and forestry production

Many fungal members of the Diatrypaceae family are pathogenic towards plants and are widely distributed globally. Cryptosphaeria pullmanensis is a pathogenic fungus that infects populus and walnut trees, causing their death. We sequenced the genome of C. pullmanensis based on a combination of Nanopore PromethION and Illumina NovaSeq PE150 platforms, and functionally annotated the sequences using a number of open-access databases. This is the first report of the genome-scale assembly and annotation for C. pullmanensis, the first species of the genus Cryptosphaeria to be sequenced. We obtained 13 contigs with an N50 contig size of 7,095,780 bp, a GC content ratio of 43.23% and a genome size of 56.72 Mb with 10,474 putative coding genes. Comparative genomic analysis against the genomes of seven Ascomycetes fungal strains was performed. Among the seven species tested, the Eutypa lata genome displayed the highest similarity to the C. pullmanensis genome in terms of collinearity and homologous gene content. This study has provided a genetic resource that offers extensive information and a framework for future investigations into the transcriptome, proteome, and metabonome of C. pullmanensis to understand its molecular pathogenesis.

A novel membraneless β-glucan/O2 enzymatic fuel cell based on β-glucosidase (RmBgl3B)/pyranose dehydrogenase (AmPDH) co-immobilized onto buckypaper electrode

A novel membraneless β-glucan/O₂ enzymatic fuel cell was developed by combining a bioanode based on buckypaper modified with co-immobilized Agaricus meleagris pyranose dehydrogenase (AmPDH) and Rhodothermus marinus β-glucosidase (RmBgl3B) (RmBgl3B-AmPDH/buckypaper) with a biocathode based on solid graphite modified with Myrothecium verrucaria bilirubin oxidase (MvBOx/graphite). AmPDH was connected electrochemically with the buckypaper using an osmium redox polymer in a mediated reaction, whereas MvBOx was connected with graphite in a direct electron transfer reaction. The fuel for the bioanode was produced by enzymatic hydrolysis of β-glucan by the exoglucanase RmBgl3B into d-glucose, which in turn was enzymatically oxidised by AmPDH to generate a current response. This design allows to obtain an efficient enzymatic fuel cell, where the chemical energy converted into electrical energy is higher than the chemical energy stored in complex carbohydrate based fuel. The maximum power density of the assembled β-glucan/O₂ biofuel cell reached 26.3 ± 4.6 μWcm^-2 at 0.36 V in phosphate buffer containing 0.5 % (w/v) β-glucan at 40 °C with excellent stability retaining 68.6 % of its initial performance after 5 days. The result confirms that β-glucan can be employed as fuel in an enzymatic biofuel cell.

Protein engineering for electrochemical biosensors

The development of electrochemical biosensors has gained tremendous attention. Protein engineering has been applied for enhancing properties of native redox enzymes, such as selectivity, sensitivity, and stability required for applicable biosensors. This review highlights recent advances of protein engineering to improve enzymatic catalysis of biosensors, facilitate electron transfer and enzyme immobilization, and construct allosteric protein biosensors. The pros and cons of different protein engineering strategies are briefly discussed, and perspectives are further provided.

Highly sensitive and stable fructose self-powered biosensor based on a self-charging biosupercapacitor

Herein, we present an alternative approach to obtain a highly sensitive and stable self-powered biosensor that was used to detect D-fructose as proof of concept.In this platform, we perform a two-step process, viz. self-charging the biosupercapacitor for a constant time by using D-fructose as fuel and using the stored charge to realize the detection of D-fructose by performing several polarization curves at different D-fructose concentrations. The proposed BSC shows an instantaneous power density release of 17.6 mW cm^-2 and 3.8 mW cm^-2 in pulse mode and at constant load, respectively. Moreover, the power density achieved for the self-charging BSC in pulse mode or under constant load allows for an enhancement of the sensitivity of the device up to 10 times (3.82 ± 0.01 mW cm^-2 mM^-1, charging time = 70 min) compared to the BSC in continuous operation mode and 100 times compared to the normal enzymatic fuel cell. The platform can potentially be employed as a self-powered biosensor in food or biomedical applications.

Phylogeny and Structure of Fatty Acid Photodecarboxylases and Glucose-Methanol-Choline Oxidoreductases

Glucose-methanol-choline (GMC) oxidoreductases are a large and diverse family of flavin-binding enzymes found in all kingdoms of life. Recently, a new related family of proteins has been discovered in algae named fatty acid photodecarboxylases (FAPs). These enzymes use the energy of light to convert fatty acids to the corresponding Cn-1 alkanes or alkenes, and hold great potential for biotechnological application. In this work, we aimed at uncovering the natural diversity of FAPs and their relations with other GMC oxidoreductases. We reviewed the available GMC structures, assembled a large dataset of GMC sequences, and found that one active site amino acid, a histidine, is extremely well conserved among the GMC proteins but not among FAPs, where it is replaced with alanine. Using this criterion, we found several new potential FAP genes, both in genomic and metagenomic databases, and showed that related bacterial, archaeal and fungal genes are unlikely to be FAPs. We also identified several uncharacterized clusters of GMC-like proteins as well as subfamilies of proteins that lack the conserved histidine but are not FAPs. Finally, the analysis of the collected dataset of potential photodecarboxylase sequences revealed the key active site residues that are strictly conserved, whereas other residues in the vicinity of the flavin adenine dinucleotide (FAD) cofactor and in the fatty acid-binding pocket are more variable. The identified variants may have different FAP activity and selectivity and consequently may prove useful for new biotechnological applications, thereby fostering the transition from a fossil carbon-based economy to a bio-economy by enabling the sustainable production of hydrocarbon fuels.

Overview of flavin-dependent enzymes

Flavin-dependent enzymes catalyze a wide variety of biological reactions that are important for all types of living organisms. Knowledge gained from studying the chemistry and biological functions of flavins and flavin-dependent enzymes has continuously made significant contributions to the development of the fields of enzymology and metabolism from the 1970s until now. The enzymes have been applied in various applications such as use as biocatalysts in synthetic processes for the chemical and pharmaceutical industries or in the biodetoxification and bioremediation of toxic or unwanted compounds, and as biosensors or biodetection tools for quantifying various agents of interest. Many flavin-dependent enzymes are also prime targets for drug development. Based on their reaction mechanisms, they can be classified into five categories: oxidase, dehydrogenase, monooxygenase, reductase, and redox neutral flavin-dependent enzymes. In this chapter, the general properties of flavin-dependent enzymes and the nature of their chemical reactions are discussed, along with their practical applications.