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International audience; Biocatalytic pathways for the synthesis of (-)-menthol, the most sold flavor worldwide, are highly sought-after. To access the key intermediate (R)-citronellal used in current major industrial production routes, we established a one-pot bienzymatic cascade from inexpensive geraniol, overcoming the problematic biocatalytic reduction of the mixture of (E/Z)-isomers in citral by harnessing a copper radical oxidase (CgrAlcOx) and an old yellow enzyme (OYE). The cascade using OYE2 delivered 95.1% conversion to (R)-citronellal with 95.9% cc, a 62 mg scaleup affording high yield and similar optical purity. An alternative OYE, GIuER, gave (S)-citronellal from geraniol with 95.3% conversion and 99.2% ee.

Global food security is endangered by fungal phytopathogens causing devastating crop production losses. Many of these pathogens use specialized appressoria cells to puncture plant cuticles. Here, we unveil a pair of alcohol oxidase–peroxidase enzymes to be essential for pathogenicity. Using Colletotrichum orbiculare, we show that the enzyme pair is cosecreted by the fungus early during plant penetration and that single and double mutants have impaired penetration ability. Molecular modeling, biochemical, and biophysical approaches revealed a fine-tuned interplay between these metalloenzymes, which oxidize plant cuticular long-chain alcohols into aldehydes. We show that the enzyme pair is involved in transcriptional regulation of genes necessary for host penetration. The identification of these infection-specific metalloenzymes opens new avenues on the role of wax-derived compounds and the design of oxidase-specific inhibitors for crop protection. Fungal phytopathogens secrete tandem metalloenzymes that catalyze cuticle oxidation and drive plant cell entry This study was supported by the “Agence Nationale de la Recherche” and by the Natural Sciences and Engineering Research Council of Canada through the ANR-NSERC project “FUNTASTIC” (ANR-17-CE07-0047, STPGP 493781-16). We are grateful to MANE & Fils and the “Association Nationale Recherche Technologie” (ANRT) for funding the Ph.D. fellowship of D.R. (grant no. 2017/1169). Work in Japan was supported by the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research—KAKENHI, grant numbers 15H05780 and 20H02989 to Y.K., and 20K15529 to S.K. Peer Reviewed "Article signat per 18 autors/es: Bastien Bissaro and Sayo Kodama and Takumi Nishiuchi and Anna Maria Díaz-Rovira and Hayat Hage and David Ribeaucourt and Mireille Haon and Sacha Grisel and A. Jalila Simaan and Fred Beisson and Stephanie M. Forget and Harry Brumer and Marie-Noëlle Rosso and Victor Guallar and Richard O’Connell and Mickaël Lafond and Yasuyuki Kubo and Jean-Guy Berrin "

International audience; 1D 1H NMR spectroscopy has been widely used to monitor enzymatic activity by recording the evolution of the spectra of substrates and/or products thanks to the linear response of NMR. For complex systems involving the coexistence of multiple compounds (substrate, final product and various intermediates), the identification and quantification can be a more arduous task. Here, we present a simple analytical method for a rapid characterization of reaction mixtures involving enzymatic complexes using Maximum Quantum (MaxQ) NMR, accelerated with the Non-Uniform Sampling (NUS) acquisition procedure. Specifically, this approach enables, in a first analytical step, to count the molecules present in the samples. We also show, using two different enzymatic systems, that the implementation of these pulse sequences implies precautions related to the short relaxation times due to the presence of metallo-enzymes or paramagnetic catalysts. Finally, the combination of MaxQ and diffusion experiments, which leads to a 3D chart, greatly improves the resolution and offers an extreme simplification of the spectra while giving valuable indications on the affinity of the enzymes to the different compounds present in the reaction mixture.

International audience; 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.

Copper radical alcohol oxidases (CRO-AlcOx), which have been recently discovered among fungal phytopathogens, are attractive for the production of fragrant fatty aldehydes. With the initial objective to investigate the secretion of CRO-AlcOx by natural fungal strains, we undertook time course analyses of the secretomes of three Colletotrichum species (C. graminicola, C. tabacum, and C. destructivum) using proteomics. The addition of a copper-manganese-ethanol mixture in the absence of any plant-biomass mimicking compounds to Colletotrichum cultures unexpectedly induced the secretion of up to 400 proteins, 29 to 52% of which were carbohydrate-active enzymes (CAZymes), including a wide diversity of copper-containing oxidoreductases from the auxiliary activities (AA) class (AA1, AA3, AA5, AA7, AA9, AA11, AA12, AA13, and AA16). Under these specific conditions, while a CRO-glyoxal oxidase from the AA5_1 subfamily was among the most abundantly secreted proteins, the targeted AA5_2 CRO-AlcOx were secreted at lower levels, suggesting heterologous expression as a more promising strategy for CRO-AlcOx production and utilization. C. tabacum and C. destructivum CRO-AlcOx were thus expressed in Pichia pastoris, and their preference toward both aromatic and aliphatic primary alcohols was assessed. The CRO-AlcOx from C. destructivum was further investigated in applied settings, revealing a full conversion of C(6) and C(8) alcohols into their corresponding fragrant aldehydes. IMPORTANCE In the context of the industrial shift toward greener processes, the biocatalytic production of aldehydes is of utmost interest owing to their importance for their use as flavor and fragrance ingredients. Copper radical alcohol oxidases (CRO-AlcOx) have the potential to become platform enzymes for the oxidation of alcohols to aldehydes. However, the secretion of CRO-AlcOx by natural fungal strains has never been explored, while the use of crude fungal secretomes is an appealing approach for industrial applications to alleviate various costs pertaining to biocatalyst production. While investigating this primary objective, the secretomics studies revealed unexpected results showing that under the oxidative stress conditions we probed, Colletotrichum species can secrete a broad diversity of copper-containing enzymes (laccases, sugar oxidoreductases, and lytic polysaccharide monooxygenases [LPMOs]) usually assigned to “plant cell wall degradation,” despite the absence of any plant-biomass mimicking compound. However, in these conditions, only small amounts of CRO-AlcOx were secreted, pointing out recombinant expression as the most promising path for their biocatalytic application.

Biocatalytic pathways for the synthesis of (−)-menthol, the most sold flavor worldwide, are highly sought-after. To access the key intermediate (R)-citronellal used in current major industrial production routes, we established a one-pot bienzymatic cascade from inexpensive geraniol, overcoming the problematic biocatalytic reduction of the mixture of (E/Z)-isomers in citral by harnessing a copper radical oxidase (CgrAlcOx) and an old yellow enzyme (OYE). The cascade using OYE2 delivered 95.1% conversion to (R)-citronellal with 95.9% ee, a 62 mg scale-up affording high yield and similar optical purity. An alternative OYE, GluER, gave (S)-citronellal from geraniol with 95.3% conversion and 99.2% ee.

Copper Radical Alcohol Oxidases (CRO-AlcOx), which have been recently discovered among fungal phytopathogens are attractive for the production of fragrant fatty aldehydes. To investigate the secretion of CRO-AlcOx by natural fungal strains, we undertook time-course analyses of the secretomes of threeColletotrichumspecies (C. graminicola, C. tabacumandC. destructivum) using proteomics. The addition of a copper-manganese-ethanol mixture toColletotrichumcultures unexpectedly induced the secretion of up to 400 proteins, 29-52% of which were carbohydrate-active enzymes (CAZymes), including a wide diversity of copper-containing oxidoreductases from the auxiliary activities (AA) class (AA1, AA3, AA5, AA7, AA9, AA11-AA13, AA16). Under these specific conditions, while a CRO-glyoxal oxidase from the AA5_1 subfamily was among the most abundantly secreted proteins, the targeted AA5_2 CRO-AlcOx were secreted at lower levels, suggesting heterologous expression as a more promising strategy for CRO-AlcOx production and utilization.C. tabacumandC. destructivumCRO-AlcOx were expressed inPichia pastorisand their preference toward both aromatic and aliphatic primary alcohols was assessed. The CRO-AlcOx fromC. destructivumwas further investigated in applied settings, revealing a full conversion of C6 and C8 alcohols into their corresponding fragrant aldehydes.IMPORTANCEIn the context of the industrial shift toward greener processes, the biocatalytic production of aldehydes is of utmost interest owing to their importance as intermediates in preparative chemistry and for their use as flavors and fragrances ingredients. In the search for new biocatalysts, CRO-AlcOx have the potential to become platform enzymes for the oxidation of alcohols to aldehydes. The use of crude fungal secretomes is often seen has an appealing approach by industries since alleviating various costs pertaining to biocatalysts production. However, the secretion of CRO-AlcOx by natural fungal strains has never been explored. This study showed thatColletotrichumspecies can secrete a broad diversity of copper-containing enzymes, but only little amount of CRO-AlcOx. Thus, recombinant expression remains the most promising approach. The potential of CRO-AlcOx as biocatalyst for flavor and fragrance applications was confirmed through the production of two new enzymes with activity on fatty alcohols.

Copper radical oxidases (CRO) form a class of enzymes with a longstanding history encompassing diverse substrate specificities. While the biological function of most CROs remains unknown, we observed that CROs active on aliphatic alcohols are found only in fungal plant pathogens. Here, we unveil the role of these CROs and the identity of their natural redox partner, a haem-iron peroxidase. Combining multiscale approaches, we report that Colletotrichum and Magnaporthe appressoria (specialized cells that puncture the plant cuticles) co-secrete this pair of metalloenzymes early during penetration. We show in vivo that mutant appressoria lacking either or both enzymes have impaired penetration ability and pathogenicity. We reveal in vitro a finely-tuned enzyme interplay is responsible for the oxidation of plant cuticular long-chain alcohols into aldehyde products, suggested to act as key molecular signals in the fungal infection machinery. Our results open new avenues to design oxidase-specific inhibitors as anti-penetrants for crop protection.

The oxidation of alcohols is a cornerstone reaction in chemistry, notably in the flavor and fragrance industry where long-chain aliphatic aldehydes are major odorant compounds. In a context where greener alternatives are sought after, biocatalysis holds many promises. Here, we investigated the ability of the alcohol oxidase from Colletotrichum graminicola (CgrAlcOx)—an organic cofactor-free enzyme belonging to the copper-radical oxidase (CRO) class—to convert industrially relevant long-chain aliphatic alcohols. CgrAlcOx is a competent catalyst for the conversion of octan-1-ol when supported by the accessory enzymes peroxidase and catalase. Detailed examination of the products revealed the occurrence of an overoxidation step leading to the production of carboxylic acid for some aliphatic aldehydes and benzaldehyde derivatives. The partition between aldehyde and acid products varied upon substrate properties (chain length and propensity to form geminal-diols) and enzyme specificity and could be tuned by controlling the reaction conditions. In silico analyses suggested an inhibitory binding mode of long-chain aliphatic geminal-diols and a substrate-induced fit mechanism for a benzyl alcohol derivative. By demonstrating their natural ability to perform long-chain aliphatic alcohol oxidation, the present study establishes the potential of fungal CRO-AlcOx as promising candidates for the green production of flavor and fragrance compounds. This study was supported by the French National Agency for Research (“Agence Nationale de la Recherche”) through the “Projet de Recherche Collaboratif International” ANR-NSERC (FUNTASTIC project, ANR-17-CE07-0047), by the Natural Sciences and Engineering Research Council of Canada through the "Strategic Projects - Natural Resources and Energy - Project (STPGP) entitled "FUNTASTIC - Fungal copper-radical oxidases as new biocatalysts for the valorization of biomass carbohydrates and alcohols" and by the PID2019-106370RB-I00 grant from the Spanish Ministry of Innovation and Sciences. We are grateful to MANE & Fils and the “Association Nationale Recherche Technologie” (ANRT) for funding the PhD fellowship of D.R. entitled “Discovery and structure-function study of new fungal copper radicals oxidases used as biocatalysts for the valorisation of alcohols and plant biomass.” This Convention Industrielle de Formation par la RecherchE (CIFRE) grant no. 2017/1169 runs from 1 April 2018 to 1 April 2021