A novel α-galactosidase from the thermophilic probiotic Bacillus coagulans with remarkable protease-resistance and high hydrolytic activity.

Rui Zhao,Ruili Zhao,Xiaoming Zhang,Yishuai Tu,Xiangdong Chen,Liping Deng,Israel Silman

doi:10.1371/journal.pone.0197067

Abstract

A novel α-galactosidase of glycoside hydrolase family 36 was cloned from Bacillus coagulans, overexpressed in Escherichia coli, and characterized. The purified enzyme Aga-BC7050 was 85 kDa according to SDS-PAGE and 168 kDa according to gel filtration, indicating that its native structure is a dimer. With p-nitrophenyl-α-d- galactopyranoside (pNPGal) as the substrate, optimal temperature and pH were 55 °C and 6.0, respectively. At 60 °C for 30 min, it retained > 50% of its activity. It was stable at pH 5.0–10.0, and showed remarkable resistance to proteinase K, subtilisin A, α-chymotrypsin, and trypsin. Its activity was not inhibited by glucose, sucrose, xylose, or fructose, but was slightly inhibited at galactose concentrations up to 100 mM. Aga-BC7050 was highly active toward pNPGal, melibiose, raffinose, and stachyose. It completely hydrolyzed melibiose, raffinose, and stachyose in < 30 min. These characteristics suggest that Aga-BC7050 could be used in feed and food industries and sugar processing.

Highlights

As important oil seed crops, soybeans are an abundant source of protein
We found that only the α-galactosidase produced by B. coagulans could strongly resist hydrolysis by protease
By analyzing the published genomes of B. coagulans in the GenBank database, we found some predicted αgalactosidase genes suggesting that this species probably can express a functional α-galactosidase

Summary

Introduction

As important oil seed crops, soybeans are an abundant source of protein. In addition to being rich in protein and plant oil, soybeans exert various health benefits, helping to reduce the incidence of human diseases such as heart-disease and cancer. Soybeans are widely used in human food and animal feed This food item contains a high content of α-galactosides, mainly including raffinose and stachyose, which monogastric animals and humans are unable to digest [1]. These compounds are digested by anaerobic bacteria in the large intestine, resulting in the production of carbon dioxide, hydrogen and a small amount of methane gas. In monogastric animals, this causes abdominal distension, diarrhea, and indigestion, along with a decrease in feed intake and growth performance [2]

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