Arabinoxylo- and Arabino-Oligosaccharides- Specific α-L-Arabinofuranosidase GH51 Isozymes from the Amylolytic Yeast Saccharomycopsis fibuligera

Two genes encoding probable alpha-L-arabinofuranosidase (E.C. 3.2.1.55) isozymes (ABFs) with 92.3% amino acid sequence identity, ABF51A and ABF51B, were found from chromosomes 3 and 5 of Saccharomycopsis fibuligera KJJ81, an amylolytic yeast isolated from Korean wheat-based nuruk, respectively. Each open reading frame consists of 1,551 nucleotides and encodes a protein of 517 amino acids with the molecular mass of approximately 59 kDa. These isozymes share approximately 49% amino acid sequence identity with eukaryotic ABFs from filamentous fungi. The corresponding genes were cloned, functionally expressed, and purified from Escherichia coli. SfABF51A and SfABF51B showed the highest activities on p-nitrophenyl arabinofuranoside at 40 similar to 45 degrees C and pH 7.0 in sodium phosphate buffer and at 50 degrees C and pH 6.0 in sodium acetate buffer, respectively. These exoacting enzymes belonging to the glycoside hydrolase (GH) family 51 could hydrolyze arabinoxylooligosaccharides (AXOS) and arabino-oligosaccharides (AOS) to produce only L-arabinose, whereas they could hardly degrade any polymeric substrates including arabinans and arabinoxylans. The detailed product analyses revealed that both SfABF51 isozymes can catalyze the versatile hydrolysis of alpha-(1,2)and alpha-(1,3)-L-arabinofuranosidic linkages of AXOS, and alpha-(1,2)-, alpha-(1,3)-, and alpha-(1,5)linkages of linear and branched AOS. On the contrary, they have much lower activity against the alpha(1,2) and alpha-(1,3)-double-substituted substrates than the single-substituted ones. These hydrolases could potentially play important roles in the degradation and utilization of hemicellulosic biomass by S. fibuligera.