Genetic characterization of the β-glucuronidase enzyme from a human intestinal bacterium, Ruminococcus gnavus

Abstract

β-Glucuronidase activity (encoded by thegusgene) has been characterized for the first time fromRuminococcus gnavusE1, an anaerobic bacterium belonging to the dominant human gut microbiota.β-Glucuronidase activity plays a major role in the generation of toxic and carcinogenic metabolites in the large intestine, as well as in the absorption and enterohepatic circulation of many aglycone residues with protective effects, such as lignans, flavonoids, ceramide and glycyrrhetinic acid, that are liberated by the hydrolysis of the corresponding glucuronides. The complete nucleotide sequence of a 4537 bp DNA fragment containing theβ-glucuronidase locus fromR. gnavusE1 was determined. Five ORFs were detected on this fragment: three complete ORFs (ORF2,gusand ORF3) and two partial ORFs (ORF4 and ORF5). The products of ORF2 and ORF3 show strong similarities with manyβ-glucoside permeases of the phosphoenolpyruvate : β-glucoside phosphotransferase systems (PTSs), such asEscherichia coliBglC,Bacillus subtilisBglP andBacillus haloduransPTS Enzyme II. The product of ORF5 presents strong similarities with the amino-terminal domain ofClostridium acetobutylicumβ-glucosidase (bglA). Thegusgene product presents similarities with several knownβ-glucuronidase enzymes, including those ofLactobacillus gasseri(69 %),E. coli(61 %),Clostridium perfringens(59 %) andStaphylococcus aureus(58 %). By complementing anE. colistrain in which theuidAgene encoding the enzyme was deleted, it was confirmed that theR. gnavus gusgene encodes theβ-glucuronidase enzyme. Moreover, it was found that thegusgene was transcribed as part of an operon that includes ORF2, ORF3 and ORF5.