Characterization of a recombinant bile salt hydrolase (BSH) from Bifidobacterium bifidum for its glycine-conjugated bile salts specificity

Abstract

Deconjugation of bile salts in vivo not only promotes the cholesterol metabolism of the host, but also provides cellular carbon, nitrogen and sulphur for some probiotics. In this study, the gene of BSH from Bifidobacterium bifidum (ATCC 29521) was amplified and expressed using glutathione S-transferase (GST) Gene Fusion System. The enzyme was purified in a mild conditions without denaturation and renaturation, and the molecular mass was estimated to be 35 kDa. The optimum pH for the enzyme catalysis was 5.5. The BSH enzyme was stable from 37 to 57 °C. In addition, this enzyme was completely inhibited by Cu2+, while many other metal ions only gave moderate inhibition. Hydrolysis efficiency of BSH was quantified in two ways: ninhydrin colouration method and high-performance liquid chromatography coupled with evaporative light scattering detector (HPLC-ELSD). The hydrolysis process was clearly observed through real-time picture monitoring. The activity of BSH on glycine-conjugated bile salts was better than on taurine-conjugated bile salts. The proportion of hydrolysis for both sodium glycochenodeoxycholate (GCDCA) and sodium glycoursodeoxycholate (GUDCA) were more than 90% in 60 min. However, the proportion of hydrolysis for sodium taurochenodeoxycholate (TCDCA) and sodium tauroursodeoxycholate (TUDCA) were only 68% and 43% at the same condition. The study of this paper provides a better choice for hydrolysis of glycine-conjugated bile salts. Highlights The specificity of BSH was high for glycine-conjugated bile salts. Hydrolysis process of bile acid was obtained through real-time picture monitoring. Hydrolysis efficiency of BSH was quantified in two ways: ninhydrin colouration method and HPLC-ELSD.