Background: β-Galactosidases catalyze both hydrolytic and transgalactosylation reactions and therefore have
many applications in food, medical, and biotechnological fields.
Aspergillus niger has been a main source of
β-galactosidase, but the properties of this enzyme are incompletely studied.
Results: Three new β-galactosidases belonging to glycosyl hydrolase family 35 from
A. niger F0215 were cloned,
expressed, and biochemically characterized. In addition to the known activity of LacA encoded by
lacA, three
putative β-galactosidases, designated as LacB, LacC, and LacE encoded by the genes
lacB,
lacC, and
lacE,
respectively, were successfully cloned, sequenced, and expressed and secreted by
Pichia pastoris
. These three
proteins and LacA have N-terminal signal sequences and are therefore predicted to be extracellular enzymes.
They have the typical structure of fungal β-galactosidases with defined hydrolytic and transgalactosylation
activities on lactose. However, their activity properties differed. In particular, LacB and lacE displayed
maximum hydrolytic activity at pH 4–5 and 50°C, while LacC exhibited maximum activity at pH 3.5 and 60°C.
All β-galactosidases performed transgalactosylation activity optimally in an acidic environment.
Conclusions: Three new β-galactosidases belonging to glycosyl hydrolase family 35 from
A. niger F0215 were
cloned and biochemically characterized. In addition to the known LacA,
A. niger has at least three
β-galactosidase family members with remarkably different biochemical properties.
