β-Glucuronidase from Lactobacillus brevis useful for baicalin hydrolysis belongs to glycoside hydrolase family 30

Abstract

Baicalin (baicalein 7-O-β-D-glucuronide) is one of the major flavonoid glucuronides found in traditional herbal medicines. Because its aglycone, baicalein, is absorbed more quickly and shows more effective properties than baicalin, the conversion of baicalin into baicalein by β-glucuronidase (GUS) has drawn the attention of researchers. Recently, we have found that Lactobacillus brevis subsp. coagulans can convert baicalin to baicalein. Therefore, we aimed to identify and characterize the converting enzyme from L. brevis subsp. coagulans. First, we purified this enzyme from the cell-free extracts of L. brevis subsp. coagulans and cloned its gene. Surprisingly, this enzyme was found to be a GUS belonging to glycoside hydrolase (GH) family 30 (designated as LcGUS30), and its amino acid sequence has little similarity with any GUS belonging to GH families 1, 2, and 79 that have been reported so far. We then established a high-level expression and simple purification system of the recombinant LcGUS30 in Escherichia coli. The detailed analysis of the substrate specificity revealed that LcGUS30 has strict specificity toward glycon but not toward aglycones. Interestingly, LcGUS30 prefers baicalin rather than estrone 3-(β-D-glucuronide), one of the human endogenous steroid hormones. These results indicated that L. brevis subsp. coagulans and LcGUS30 should serve as powerful tools for the construction of a safe bioconversion system for baicalin. In addition, we propose that this novel type of GUS forms a new group in subfamily 3 of GH family 30.

Properties and applications of β‐glycosidase from Bacteroides thetaiotaomicron that specifically hydrolyses isoflavone glycosides

“…Numerous studies on GHs have been performed in bacteria, plants and fungi (Yang et al ., ; Yin et al ., ; Chuankhayan et al ., ; Kaya et al ., ; Kuo & Lee, ; Choi et al ., ; Hu et al ., ; Xue et al ., ; Kim et al ., , ; Song et al ., ; Li et al ., ; Sakurama et al ., ). However, our understanding of β‐glucosidases from B. thetaiotaomicron remains limited.…”

Human microbiome signatures of differential colorectal cancer drug metabolism

“… 30 , 31 In addition to irinotecan, examples include paracetamol, codeine, chloramphenicol, vitamins, and tamoxifen. 30 – 34 An unanswered question is how the microbiome influences variability in community level conversion efficiency of these glucuronidated substrates. Our study presents a framework to address this question.…”

A Novel β-Glucuronidase from Talaromyces pinophilus Li-93 Precisely Hydrolyzes Glycyrrhizin into Glycyrrhetinic Acid 3- O -Mono-β- d -Glucuronide

“…Most of the GUSs used for biotransformation of natural glucuronides showed much higher binding affinities and catalytic activities on artificial substrates than on the natural glucuronides. For instance, the K m value of LcGUS30 (from Lactobacillus brevis) for baicalin is 11-fold higher than that for pNP-␤-GlcA, and its catalytic efficiency (k cat /K m ) on pNP-␤-GlcA is 19-fold higher than that on baicalin (44). Both PGUS-E and PGUS-P showed much lower K m values and higher k cat /K m values on pNP-␤-GlcA than on GL (40).…”

“…Moreover, TpGUS79A also displays activity on flavonoid glucuronides, such as quercetin 3-glucuronide and baicalin. However, its activity on baicalin (k cat /K m value of 0.29 mM Ϫ1 s Ϫ1 ; specific activity of 0.565 U mg Ϫ1 ) is much lower than those of the GUSs with high specificity for baicalin (Table S2), such as LcGUS30 (44) and SvGUS (42). So far, the GUSs specifically hydrolyzing quercetin 3-glucuronide have rarely been reported.…”