α-L-rhamnosidase: production, properties, and applications

A sustainable and efficient strategy for bioconverting naringin to L-rhamnose, 2R-naringenin, and kaempferol

The development of a sustainable and efficient bioconversion strategy is crucial for the full-component utilization of naringin. In this study, an engineering Pichia pastoris co-culture system was developed to produce L-rhamnose and 2S/2R-naringenin. By optimizing transformation conditions, the co-culture system could completely convert naringin while fully consuming glucose. The production of 2S/2R-naringenin reached 59.5 mM with a molar conversion of 99.2%, and L-rhamnose reached 59.1 mM with a molar conversion of 98.5%. In addition, an engineering Escherichia coli co-culture system was developed to produce 2R-naringenin and kaempferol from 2S/2R-naringenin. Maximal kaempferol production reached 1050 mg/L with a corresponding molar conversion of 99.0%, and 996 mg/L 2R-naringenin was accumulated. Finally, a total of 17.4 g 2R-naringenin, 18.0 g kaempferol, and 26.1 g L-rhamnose were prepared from 100 g naringin. Thus, this study provides a novel strategy for the production of value-added compounds from naringin with an environmentally safe process.

Efficient biosynthesis of prunin in methanol cosolvent system by an organic solvent-tolerant α-L-rhamnosidase from Spirochaeta thermophila

Prunin of desirable bioactivity and bioavailability can be transformed from plant-derived naringin by the key enzyme α-L-rhamnosidase. However, the production was limited by unsatisfactory properties of α-L-rhamnosidase such as thermostability and organic solvent tolerance. In this study, biochemical characteristics, and hydrolysis capacity of a novel α-L-rhamnosidase from Spirochaeta thermophila (St-Rha) were investigated, which was the first characterized α-L-rhamnosidase for Spirochaeta genus. St-Rha showed a higher substrate specificity towards naringin and exhibited excellent thermostability and methanol tolerance. The Km of St-Rha in the methanol cosolvent system was decreased 7.2-fold comparing that in the aqueous phase system, while kcat/Km value of St-Rha was enhanced 9.3-fold. Meanwhile, a preliminary conformational study was implemented through comparative molecular dynamics simulation analysis to explore the mechanism underlying the methanol tolerance of St-Rha for the first time. Furthermore, the catalytic ability of St-Rha for prunin preparation in the 20% methanol cosolvent system was explored, and 200 g/L naringin was transformed into 125.5 g/L prunin for 24 h reaction with a corresponding space-time yield of 5.2 g/L/h. These results indicated that St-Rha was a novel α-L-rhamnosidase suitable for hydrolyzing naringin in the methanol cosolvent system and provided a better alternative for improving the efficient production yield of prunin.

Aspergillus oryzae α-l-rhamnosidase: Crystal structure and insight into the substrate specificity

The subsequent biochemical and structural investigations of the purified recombinant α-l-rhamnosidase from Aspergillus oryzae expressed in Pichia pastoris, designated as rAoRhaA, were performed. The specific activity of the rAoRhaA wild-type was higher toward hesperidin and narirutin, where the l-rhamnose residue was α-1,6-linked to β-d-glucoside, than toward neohesperidin and naringin with an α-1,2-linkage to β-d-glucoside. However, no activity was detected toward quercitrin, myricitrin, and epimedin C. rAoRhaA kinetic analysis indicated that Km values for neohesperidin, naringin, and rutin were lower compared to those for hesperidin and narirutin. kcat values for hesperidin and narirutin were higher than those for neohesperidin, naringin, and rutin. High catalytic efficiency (kcat /Km ) toward hesperidin and narirutin was a result of a considerably high kcat value, while Km values for hesperidin and narirutin were higher than those for naringin, neohesperidin, and rutin. The crystal structure of rAoRhaA revealed that the catalytic domain was represented by an (α/α)6 -barrel with the active site located in a deep cleft and two β-sheet domains were also present in the N- and C-terminal sites of the catalytic domain. Additionally, five asparagine-attached N-acetylglucosamine molecules were observed. The catalytic residues of AoRhaA were suggested to be Asp254 and Glu524, and their catalytic roles were confirmed by mutational studies of D254N and E524Q variants, which lost their activity completely. Notably, three aspartic acids (Asp117, Asp249, and Asp261) located at the catalytic pocket were replaced with asparagine. D117N variant showed reduced activity. D249N and D261N variants activities drastically decreased.

A High-Quality Genome Sequence of the Penicillium oxalicum 5-18 Strain Isolated from a Poplar Plantation Provides Insights into Its Lignocellulose Degradation

Studies on the degradation of plant cell wall polysaccharides by fungal extracellular enzymes have attracted recent attention from researchers. Xylan, abundant in hemicellulose, that play great role in connection between cellulose and lignin, has seen interest in its hydrolytic enzymatic complex. In this study, dozens of fungus species spanning genera were isolated from rotting leaves based on their ability to decompose xylan. Among these isolates, a strain with strong xylanase-producing ability was selected for further investigation by genome sequencing. Based on phylogenetic analysis of ITS (rDNA internal transcribed spacer) and LSU (Large subunit 28S rDNA) regions, the isolate was identified as Penicillium oxalicum. Morphological analysis also supported this finding. Xylanase activity of this isolated P. oxalicum 5-18 strain was recorded to be 30.83 U/mL using the 3,5-dinitro-salicylic acid (DNS) method. Further genome sequencing reveals that sequenced reads were assembled into a 30.78 Mb genome containing 10,074 predicted protein-encoding genes. In total, 439 carbohydrate-active enzymes (CAZymes) encoding genes were predicted, many of which were associated with cellulose, hemicellulose, pectin, chitin and starch degradation. Further analysis and comparison showed that the isolate P. oxalicum 5-18 contains a diverse set of CAZyme genes involved in degradation of plant cell wall components, particularly cellulose and hemicellulose. These findings provide us with valuable genetic information about the plant biomass-degrading enzyme system of P. oxalicum, facilitating a further exploration of the repertoire of industrially relevant lignocellulolytic enzymes of P. oxalicum 5-18.