Fungal β-Glycosidase Belonging to Subfamily 4 of Glycoside Hydrolase Family 30 with Transglycosylation Activity

Semi-rational engineering of an α-L-fucosidase for regioselective synthesis of fucosyl-N-acetylglucosamine disaccharides

α-L-Fucosidases are attractive biocatalysts for the production of bioactive fucosylated oligosaccharides, however, poor regioselectivity and activity for transglycosylation have significantly limited their applications. We have recently derived an α-L-Fucosidase, BF3242, from Bacteroides fragilis NCTC9343, which could efficiently synthesize a mixture of Fuc-α-1,3/1,6-GlcNAc, but its 1,3/1,6-regioselectivity was observably affected by reaction temperature. Here, we integrated loop-targeted random mutagenesis and site-directed mutagenesis to engineer the regioselectivity and transglycosylation activity of BF3242. Loop-targeted random mutagenesis revealed that L266 in the loop-4 (H242-S267) within the model of BF3242 was a key residue for the regioselectivity for transglycosylation, and the saturation mutagenesis at residue L266 uncovered a mutant L266H with a significantly increased 1,3-regioselectivity of 97 % from 69 % of WT BF3242. Subsequently, five designed single-site mutations at the putative aglycone subsites were performed, resulting in a double-site mutant L266H/M285C that increased the overall yield of Fuc-α-1,3/1,6-GlcNAc to 76 % from 68 % of WT BF3242. The saturation mutagenesis at residue M285 finally generated a double-site mutant L266H/M285T with the maximal overall yield of Fuc-α-1,3/1,6-GlcNAc of 85 % and 1,3-regioselectivity of 98 %. The R T/H of L266H/M285T was approximately 2.7-fold higher than that of the WT BF3242. Molecular dynamics simulations revealed that the structural flexibility of the loop-4 was substantially reduced in mutant L266H, and the hydrogen bond formation and binding affinity between mutant L266H/M285T and Fuc-α-1,3-GlcNAc was significantly enhanced. The semi-rationally engineered enzyme L266H/M285T would be a promising biocatalyst for highly 1,3-regioselective synthesis of fucosyl-N-acetylglucosamine disaccharide.

Enzymatic and structural properties of a novel oxalate decarboxylase BsOxdC from Bacillus safensis and its potential pH-dependent catalytic mechanism

Oxalate decarboxylase converts oxalate to formate and CO2 without requiring organic cofactors, making it biotechnologically relevant for applications in food, agriculture, and diagnostics. Its activity is highly dependent on pH; however, the pH-dependent catalytic mechanism remains poorly understood. This study identified a novel oxalate decarboxylase, BsOxdC, from Bacillus safensis and investigated its catalytic properties through heterologous expression and enzymatic assays. The purified BsOxdC efficiently degrades oxalate at an optimum temperature of 50 °C and a pH of 4.0, achieving a Vmax of 8.54 μmol/(min·mg). The apparent values of kcat, Km, and kcat/Km were 85.35 s-1, 4.67 μM, and 18.28 μM/s, respectively. The predicted structure of BsOxdC features two conserved cupin barrel folds at the N-terminal and C-terminal. Additionally, the docking model of the oxalate-BsOxdC complex is more stable than those of the formate-BsOxdC or acetate-BsOxdC complexes due to its lowest binding energy. In the open conformation of BsOxdC, the carboxyl group of the catalytic residue E181, located in the active loop S180E181N182S183T184, points away from both the oxalate and the active-site Mn ion. Simulations suggest that S180 and E181 interact with the substrate via ionic bonds and/or water bridges only at low pH (4.0), not at pH 8.0. Additionally, THR184 forms more molecular interactions with oxalate at pH 4.0 than at pH 8.0.

A Novel Bacillus Velezensis for Efficient Degradation of Zearalenone

Zearalenone (ZEN) is considered one of the most serious mycotoxins contaminating grains and their by-products, causing significant economic losses in the feed and food industries. Biodegradation pathways are currently considered the most efficient solution to remove ZEN contamination from foods. However, low degradation rates and vulnerability to environmental impacts limit the application of biodegradation pathways. Therefore, the main research objective of this article was to screen strains that can efficiently degrade ZEN and survive under harsh conditions. This study successfully isolated a new strain L9 which can efficiently degrade ZEN from 108 food ingredients. The results of sequence alignment showed that L9 is Bacillus velezensis. Meanwhile, we found that the L9 degradation rate reached 91.14% at 24 h and confirmed that the primary degradation mechanism of this strain is biodegradation. The strain exhibits resistance to high temperature, acid, and 0.3% bile salts. The results of whole-genome sequencing analysis showed that, it is possible that the strain encodes the key enzyme, such as chitinase, carboxylesterases, and lactone hydrolase, that work together to degrade ZEN. In addition, 227 unique genes in this strain are primarily involved in its replication, recombination, repair, and protective mechanisms. In summary, we successfully excavated a ZEN-degrading, genetically distinct strain of Bacillus velezensis that provides a solid foundation for the detoxification of feed and food contamination in the natural environment.

Fungal Glycosidases in Sporothrix Species and Candida albicans

Glycoside hydrolases (GHs) are enzymes that participate in many biological processes of fungi and other organisms by hydrolyzing glycosidic linkages in glycosides. They play fundamental roles in the degradation of carbohydrates and the assembly of glycoproteins and are important subjects of studies in molecular biology and biochemistry. Based on amino acid sequence similarities and 3-dimensional structures in the carbohydrate-active enzyme (CAZy), they have been classified in 171 families. Members of some of these families also exhibit the activity of trans-glycosydase or glycosyl transferase (GT), i.e., they create a new glycosidic bond in a substrate instead of breaking it. Fungal glycosidases are important for virulence by aiding tissue adhesion and colonization, nutrition, immune evasion, biofilm formation, toxin release, and antibiotic resistance. Here, we review fungal glycosidases with a particular emphasis on Sporothrix species and C. albicans, two well-recognized human pathogens. Covered issues include a brief account of Sporothrix, sporotrichosis, the different types of glycosidases, their substrates, and mechanism of action, recent advances in their identification and characterization, their potential biotechnological applications, and the limitations and challenges of their study given the rather poor available information.