A novel glycoside hydrolase family 42 enzyme with bifunctional β-galactosidase and α-L-arabinopyranosidase activities and its synergistic effects with cognate glycoside hydrolases in plant polysaccharides degradation.

GH42 enzymes are potential candidates for bifunctional β-galactosidase/α-L-arabinopyranosidase. A novel GH42 enzyme (BaBgal42A) from Bacillus was identified, the recombinant BaBgal42A hydrolyzed not only β-D-galactopyranosidic bonds in pNP-β-D-galactopyranoside, oNP-β-D-galactopyranoside, lactose, galactan, and arabinan but also α-L-arabinopyranosidic linkages in pNP-α-L-arabinopyranoside, wheat arabinoxylan and galactan. The K values of BaBgal42A for pNP-β-D-galactopyranoside and pNP-α-L-arabinopyranoside were 2.76 and 16.23 mM, respectively. Investigation of cooperative activities of BaBgal42A with cognate enzymes revealed that BaBgal42A showed obvious synergy with an endo-β-1,4-galactanase (BaGal53A) in the decomposition of galactan, supplementing BaBgal42A resulted in a 0.56-fold increase in the release of reducing sugars; BaBgal42A also exhibited a little synergy with its cognate endoxylanase (BaXynA)/α-L-arabinofuranosidase (BaAraA) in hydrolyzing wheat arabinoxylan/arabinan, addition of BaBgal42A released 12.7%/7.8% more reducing sugars than that produced by BaXynA/BaAraA alone. Moreover, BaBgal42A is a cold-adapted enzyme, exhibiting 28-46% of the maximal activity at the range of 5-20 °C and its activity was slightly stimulated by addition of Na, K, or Ca at low concentrations. This study not only expands the diversity within GH42 family, but also provides new insights into the role of microbial GH42 enzymes, which would contribute to its potential application in polysaccharides degradation and milk lactose hydrolysis.