Expression and biochemical characterization of recombinant α-l-rhamnosidase r-Rha1 from Aspergillus niger JMU-TS528

A putative cDNA of α-l-rhamnosidase was PCR-cloned from Aspergillus niger JMU-TS528 and further extracellular over-expressed in Pichia pastoris GS115. The activity of the recombinant α-l-rhamnosidase r-Rha1 was 711.9U/mL, eightfold higher than the native α-l-rhamnosidase from A. niger JMU-TS528. r-Rha1 is a N-glycosylated protein of 90kDa and possesses broad substrate specificities by hydrolyzing α-1,2, α-1,3 α-1,4, and α-1,6 linkages to β-d-glucosides. This is the first report presenting that α-l-rhamnosidase showed activity on four kinds of glucosidic linkages. Compared with other previously characterized α-l-rhamnosidases, r-Rha1 showed a good thermostability and wide range of pH-stability with the optimum pH of 5.0 and temperature of 60°C. r-Rha1 activity was not greatly affected by representative metal ions and other detected effectors and showed excellent tolerance abilities against glucose and ethanol. These beneficial characteristics of r-Rha1 suggest that r-Rha1 should be considered a potential new biocatalyst for food and drug industrial applications.