Penicillium purpurogenum produces a novel endo-1,5-arabinanase, active on debranched arabinan, short arabinooligosaccharides and on the artificial substrate p-nitrophenyl arabinofuranoside

Penicillium purpurogenum secretes numerous lignocellulose-degrading enzymes, including four arabinofuranosidases and an exo-arabinanase. In this work, the biochemical properties of an endo-arabinanase (ABN1) are presented. A gene, coding for a potential ABN was mined from the genome. It includes three introns. The cDNA is 975 bp long and codes for a mature protein of 324 residues. The cDNA was expressed in Pichia pastoris. The enzyme is active on debranched arabinan and arabinooligosaccharides. In contrast to other characterized ABNs, inactive on p-nitrophenyl-α-L-arabinofuranoside (pNPAra), ABN1 is active on this substrate. The enzyme has an optimal pH of 4.5 and an optimal temperature of 30–35 °C. Calcium does not activate ABN1. ABN1 belongs to GH family 43 sub-family 6, and a Clustal alignment with sequences of characterized fungal ABNs shows highest identity (54.6%) with an ABN from Aspergillus aculeatus. A three-dimensional model of ABN1 was constructed and the docking with pNPAra was compared with similar models of an enzyme very active on this substrate and another lacking activity, both from GH family 43. Differences in the number of hydrogen bonds between enzyme and substrate, and distance between the substrate and the catalytic residues may explain the differences in activity shown by these enzymes.