Journal
EUROPEAN JOURNAL OF BIOCHEMISTRY
Volume 269, Issue 1, Pages 249-258Publisher
WILEY
DOI: 10.1046/j.0014-2956.2001.02641.x
Keywords
heterologous expression; xenobiotic metabolism; flavonoids; isoflavones; first-pass metabolism
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Human tissues such as liver, small intestine, spleen and kidney contain a cytosolic beta-glucosidase (CBG) that hydrolyses various beta-D-glycosides, but whose physiological function is not known. Here, we describe the first heterologous expression of human CBG, a system that facilitated a detailed assessment of the enzyme specificity towards dietary glycosides. A full-length CBG cDNA (cbg-1) was cloned from a human liver cDNA library and expressed in the methylotrophic yeast Pichia pastoris at a secretion yield of approximate to10 mg.L-1. The recombinant CBG (reCBG) was purified from the supernatant using a single chromatography step and was shown to be similar to the native enzyme isolated from human liver in terms of physical properties and specific activity towards 4-nitrophenyt-beta-D-glucoside. Furthermore, the reCBG displayed a broad specificity with respect to the glycone moiety of various aryl-glycosides (beta-D-fucosides, alpha-L-arabinosides, beta-D-glucosides, beta-D-galactosides, beta-L-xylosides, beta-D-arabinosides), similar to the native enzyme. For the first time, we show that the human enzyme has significant activity towards many common dietary xenobiotics including glycosides of phytoestrogens, flavonoids, simple phenolics and cyanogens with higher apparent affinities (K-m) and specificities (k(cat)/K-m) for dietary xenobiotics than for other aryl-glyco sides. These data indicate that human CBG hydrolyses a broad range of dietary glucosides and may play a critical role in xenobiotic metabolism.
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