Identification and characterization of three Penicillium chrysogenum α-l-arabinofuranosidases (PcABF43B, PcABF51C, and AFQ1) with different specificities toward arabino-oligosaccharides.

We previously described four α-l-arabinofuranosidases (ABFs) secreted by Penicillium chrysogenum 31B. Here, we cloned the fifth and sixth genes (Pcabf43B and Pcabf51C) encoding the ABFs PcABF43B and PcABF51C in this strain and overexpressed these genes in Escherichia coli. The deduced amino acid sequences of PcABF43B and PcABF51C were highly similar to putative ABFs belonging to glycoside hydrolase families 43 and 51, respectively. Semiquantitative reverse transcription polymerase chain reaction indicated that both genes were induced by arabinose, arabinitol, arabinan, and arabinoxylan; however, the Pcabf51C gene was constitutively expressed at low levels in P. chrysogenum 31B. PcABF43B had optimal activity at 20°C and pH 5-6, indicating that this enzyme was psychrophilic and had the lowest optimal temperature reported for ABFs. PcABF51C had optimal activity at 45°C and pH 6-7. Both recombinant enzymes showed high activity on arabino-oligosaccharides, but little activity on arabinose-containing polysaccharides, such as l-arabinan. Next, we compared the substrate specificities of PcABF43B, PcABF51C, and AFQ1, a P. chrysogenum ABF that preferentially degraded oligosaccharides over polysaccharides. PcABF43B was found to preferentially hydrolyze (1→3)-linkages in branched arabino-oligosaccharides and released only a small amount of arabinose from linear α-1,5-arabino-oligosaccharides. In contrast, AFQ1 and PcABF51C showed higher activities on linear arabino-oligosaccharides than on branched arabino-oligosaccharides. AFQ1 showed high catalytic efficiencies for α-1,5-l-arabinofuranobiose (α-1,5-Ara2) and α-1,5-l-arabinofuranotriose (α-1,5-Ara3) at the same level. In contrast, intracellular PcABF51C showed much higher catalytic efficiency for α-1,5-Ara2 than for α-1,5-Ara3.