Plant tissue cultures as sources of new ene- and ketoreductase activities

Abstract

While many redox enzymes are nowadays available for synthetic applications, the toolbox of ene-reductases is still limited. Consequently, the screening for these enzymes from diverse sources in the search of new biocatalyst suitable for green chemistry approaches is needed. Among 13 plant tissue cultures, Medicago sativa and Tessaria absinthioides calli, as well as Capsicum annuum hairy roots, were selected due to their ability to hydrogenate the CC double bond of the model substrate 2-cyclohexene-1-one. The three axenic plant cultures showed more preference toward highly activated molecules such as nitrostyrene and maleimide rather than the classical substrates of the well-known Old Yellow Enzymes, resembling the skills of the NAD(P)H-dependent flavin-independent enzymes. When the three biocatalytic systems were applied in the reduction of chalcones, T. absinthioides showed high chemoselectivity toward the CC double bond whereas the other two demonstrated abilities to biohydrogenate the CC double bounds and the carbonyl groups in a sequential fashion.

Plant-Mediated Biotransformations of S(+)- and R(–)-Carvones

“…1.3.1.x), which are dependent on flavin mononucleotide. Most of them belong to the "Old Yellow Enzyme" family (OYE) and are involved in the metabolism of fatty acids or in the detoxification process [26]. Although a number of enzymes in this group have been isolated and tested even with the use of microorganisms; in practice, entire cultures are utilized.…”

“…In order to verify the course of the biotransformation over time, a suitable number of flasks with biocatalysts were prepared as described above in the screening procedure. The reactions were terminated after 1,2,3,5,22,23,26,28,45, and 48 h in the case of (4R)-(-)-carvone (1) and after 2, 4, 6, 8, 10, 12, 24, 28, and 48 h for (4S)-(+)-carvone (6).…”

Non-Conventional Yeasts as Sources of Ene-Reductases for the Bioreduction of Chalcones

“…Ene-reductases (ERs) belong to the flavin-containing "Old Yellow Enzyme" family (OYE, EC 1.6.99.1), which includes a class of I flavin-dependent oxidoreductases, which have been extensively studied for their ability to catalyze the asymmetric reduction of electronically activated C=C bonds, possessing electron-withdrawing substituents in the presence of cofactor-recycling systems for NAD(P)H [4][5][6][7][8][9][10][11][12][13][14]. Intracellular ER homologues from bacteria, yeasts, filamentous fungi and higher plants have been isolated and characterized since the 1990s [15][16][17][18][19][20][21][22][23][24][25].…”

“…Recently, whole-cells and enzymes catalyzing the C=C hydrogenation and C=O reduction of representative chalcones have been studied for obtaining compounds possessing noteworthy bioactivities. In particular, some dihydrochalcones (achieved via bioreduction of the C=C double bond) have been found to express antioxidant, UV-protective and pro-health activities, which could be interesting for pharmaceutical and cosmetic industries [25,30]. Moreover, their sweet taste make them attractive for producing sweeteners [31,32].…”

Metagenomic ene-reductases for the bioreduction of sterically challenging enones

“…To date, novel ERs have been identied from bacteria, fungi and plants mainly by conventional microbial screening, genome mining and more recently by a protein data bank search guided by catalytic site structural information. 5,[15][16][17] Nextgeneration sequencing technologies and omics approaches have opened up the opportunity to speed up the discovery of useful biocatalysts by providing access to unexplored environmental microbial communities. 18 In a previous study, we have reported a sequence-based functional metagenomics approach to identify novel biocatalysts.…”