Properties of a novel α-galactosidase from Streptomyces sp. S27 and its potential for soybean processing

A full-length α-galactosidase gene (2226 bp) was cloned from Streptomyces sp. S27 ACCC 41168 and overexpressed in Escherichia coli. The deduced amino acid sequence shared highest identities of 82% with a putative α-galactosidase from Nocardiopsis dassonvillei subsp. dassonvillei DSM 43111 and 46% with a known α-galactosidase from Bifidobacterium bifidum NCIMB 41171, both of which belong to glycoside hydrolase (GH) family 36. The purified recombinant enzyme showed a single protein band of ∼82 kDa on SDS-PAGE and three bands of ∼220, 320 and 480 kDa on non-denaturing gradient PAGE, respectively, indicating its native structure of trimer, tetramer or hexamer. The enzyme exhibited optimal activity at conditions of 35 °C and pH 7.4, similar to the intestinal conditions of mammals and poultry, was resistant to some neutral proteases (α-chymotrypsin, subtilisin A and collagenase), and showed hydrolytic ability to natural substrates, including melibiose, stachyose, raffinose and soybean meal. When combined with intestinal proteases, the enzyme showed higher hydrolytic ability to raffinose family oligosaccharides (RFOs) in soybean product. These favorable properties make the Streptomyces sp. S27 α-galactosidase very prospective in soybean processing for food and feed industries.