Properties, Physiological Functions and Involvement of Basidiomycetous Alcohol Oxidase in Wood Degradation

Extensive research efforts have been devoted to describing yeast alcohol oxidase (AO) and its promoter region, which is vastly applied in studies of heterologous gene expression. However, little is known about basidiomycetous AO and its physiological role in wood degradation. This review describes several alcohol oxidases from both white and brown rot fungi, highlighting their physicochemical and kinetic properties. Moreover, the review presents a detailed analysis of available AO-encoding gene promoter regions in basidiomycetous fungi with a discussion of the manipulations of culture conditions in relation to the modification of alcohol oxidase gene expression and changes in enzyme production. The analysis of reactions catalyzed by lignin-modifying enzymes (LME) and certain lignin auxiliary enzymes (LDA) elucidated the possible involvement of alcohol oxidase in the degradation of derivatives of this polymer. Combined data on lignin degradation pathways suggest that basidiomycetous AO is important in secondary reactions during lignin decomposition by wood degrading fungi. With numerous alcoholic substrates, the enzyme is probably engaged in a variety of catalytic reactions leading to the detoxification of compounds produced in lignin degradation processes and their utilization as a carbon source by fungal mycelium.

Biocatalytic oxidation of fatty alcohols into aldehydes for the flavors and fragrances industry

From Egyptian mummies to the Chanel n°5 perfume, fatty aldehydes have long been used and keep impacting our senses in a wide range of foods, beverages and perfumes. Natural sources of fatty aldehydes are threatened by qualitative and quantitative variability while traditional chemical routes are insufficient to answer the society shift toward more sustainable and natural products. The production of fatty aldehydes using biotechnologies is therefore the most promising alternative for the flavors and fragrances industry. In this review, after drawing the portrait of the origin and characteristics of fragrant fatty aldehydes, we present the three main classes of enzymes that catalyze the reaction of fatty alcohols oxidation into aldehydes, namely alcohol dehydrogenases, flavin-dependent alcohol oxidases and copper radical alcohol oxidases. The constraints, challenges and opportunities to implement these oxidative enzymes in the flavors and fragrances industry are then discussed. By setting the scene on the biocatalytic production of fatty aldehydes, and providing a critical assessment of its potential, we expect this review to contribute to the development of biotechnology-based solutions in the flavors and fragrances industry.

Covalent Linkage of an R-ω-Transaminase to a d-Amino Acid Oxidase through Protein Splicing to Enhance Enzymatic Catalysis of Transamination

R-ω-Transaminases (RTAs) catalyse the conversion of R-configured amines [e.g., (R)-1-phenylethylamine] into the corresponding ketones (e.g., acetophenone), by transferring an amino group from an amino donor [e.g., (R)-1-phenylethylamine] onto an amino acceptor (e.g., pyruvate), resulting in a co-product (e.g., d-alanine). d-Alanine can be deaminated back to pyruvate by d-amino acid oxidase (DAAOs). Here, through in vivo subunit splicing, the N terminus of an RTA subunit (RTA^S ) was specifically ligated to the C terminus of a DAAO subunit (DAAO^S ) through native peptide bonds (RTA&DAAO). RTA^S is in close proximity to DAAO^S , at a molecular-scale distance. Thus the transfer of pyruvate and d-alanine between RTA and DAAO can be directional and efficient. Pyruvate→d-alanine→pyruvate cycles are efficiently formed, thus promoting the forward transamination reaction. In a different, in vitro noncovalent approach, based on coiled-coil association, the RTA^S N terminus was specifically associated with the DAAO^S C terminus (RTA#DAAO). In addition, the two mixed individual enzymes (RTA+DAAO) were also studied. RTA&DAAO has a shorter distance between the paired subunits (RTA^S -DAAO^S ) than RTA#DAAO, and the number of the paired subunits is higher than in the case of RTA#DAAO, whereas RTA+DAAO cannot form the paired subunits. RTA&DAAO exhibited a transamination catalysis efficiency higher than that of RTA#DAAO and much higher than that of RTA+DAAO.

Multi-point enzyme immobilization, surface chemistry, and novel platforms: a paradigm shift in biocatalyst design

Engineering enzymes with improved catalytic properties in non-natural environments have been concerned with their diverse industrial and biotechnological applications. Immobilization represents a promising but straightforward route, and immobilized biocatalysts often display higher activities and stabilities compared to free enzymes. Owing to their unique physicochemical characteristics, including the high-specific surface area, exceptional chemical, electrical, and mechanical properties, efficient enzyme loading, and multivalent functionalization, nano-based materials are postulated as suitable carriers for biomolecules or enzyme immobilization. Enzymes immobilized on nanomaterial-based supports are more robust, stable, and recoverable than their pristine counterparts, and are even used for continuous catalytic processes. Furthermore, the unique intrinsic properties of nanomaterials, particularly nanoparticles, also confer the immobilized enzymes to be used for their broader applications. Herein, an effort has been made to present novel potentialities of multi-point enzyme immobilization in the current biotechnological sector. Various nano-based platforms for enzyme/biomolecule immobilization are discussed in the second part of the review. In summary, recent developments in the use of nanomaterials as new carriers to construct robust nano-biocatalytic systems are reviewed, and future trends are pointed out in this article.

Stabilization of Multimeric Enzymes against Heat Inactivation by Chitosan-graft-poly(N-isopropylacrylamide) in Confined Spaces

The inactivation of multimeric enzymes is a more complicated process compared with that of monomeric enzymes. Stabilization of multimeric enzymes is regarded as a challenge with practical values in enzyme technology. Temperature-sensitive copolymer chitosan-graft- poly(N-isopropylacrylamide) was synthesized and encapsulated with multimeric enzymes in the confined spaces constructed by the W/O microemulsion. In this way, the quaternary structures of multimeric enzymes are stabilized and the thermal stabilities of them are enhanced. The whole process was studied and discussed. This method, which works well for both glucose oxidase and catalase, can be developed as a general protection strategy for multimeric enzymes.

The substrate tolerance of alcohol oxidases

Alcohols are a rich source of compounds from renewable sources, but they have to be activated in order to allow the modification of their carbon backbone. The latter can be achieved via oxidation to the corresponding aldehydes or ketones. As an alternative to (thermodynamically disfavoured) nicotinamide-dependent alcohol dehydrogenases, alcohol oxidases make use of molecular oxygen but their application is under-represented in synthetic biotransformations. In this review, the mechanism of copper-containing and flavoprotein alcohol oxidases is discussed in view of their ability to accept electronically activated or non-activated alcohols and their propensity towards over-oxidation of aldehydes yielding carboxylic acids. In order to facilitate the selection of the optimal enzyme for a given biocatalytic application, the substrate tolerance of alcohol oxidases is compiled and discussed: Substrates are classified into groups (non-activated prim- and sec-alcohols; activated allylic, cinnamic and benzylic alcohols; hydroxy acids; sugar alcohols; nucleotide alcohols; sterols) together with suitable alcohol oxidases, their microbial source, relative activities and (stereo)selectivities.

Genome sequence and analysis of methylotrophic yeast Hansenula polymorpha DL1

BACKGROUND

Hansenula polymorpha DL1 is a methylotrophic yeast, widely used in fundamental studies of methanol metabolism, peroxisome biogenesis and function, and also as a microbial cell factory for production of recombinant proteins and metabolic engineering towards the goal of high temperature ethanol production.

RESULTS

We have sequenced the 9 Mbp H. polymorpha DL1 genome and performed whole-genome analysis for the H. polymorpha transcriptome obtained from both methanol- and glucose-grown cells. RNA-seq analysis revealed the complex and dynamic character of the H. polymorpha transcriptome under the two studied conditions, identified abundant and highly unregulated expression of 40% of the genome in methanol grown cells, and revealed alternative splicing events. We have identified subtelomerically biased protein families in H. polymorpha, clusters of LTR elements at G + C-poor chromosomal loci in the middle of each of the seven H. polymorpha chromosomes, and established the evolutionary position of H. polymorpha DL1 within a separate yeast clade together with the methylotrophic yeast Pichia pastoris and the non-methylotrophic yeast Dekkera bruxellensis. Intergenome comparisons uncovered extensive gene order reshuffling between the three yeast genomes. Phylogenetic analyses enabled us to reveal patterns of evolution of methylotrophy in yeasts and filamentous fungi.

CONCLUSIONS

Our results open new opportunities for in-depth understanding of many aspects of H. polymorpha life cycle, physiology and metabolism as well as genome evolution in methylotrophic yeasts and may lead to novel improvements toward the application of H. polymorpha DL-1 as a microbial cell factory.