Background: Filamentous fungi produce various mannanolytic enzymes including β-1,4-mannanases for β-mannan degradation.Results: Fungal β-1,4-mannanase, Man134A, has an unusual sequence and substrate specificity that differs from Man5C belonging to the GH5 family.Conclusion: Man134A is involved in β-mannan degradation in vivo.Significance: An Aspergillus nidulans β-1,4-mannanase reveals a novel glycoside hydrolase family, GH134.

A β-1,4-mannanase, termed AoMan134A, that belongs to the GH 134 family was identified in the filamentous fungus Aspergillus oryzae. Recombinant AoMan134A was expressed in Pichia pastoris, and the purified enzyme produced mannobiose, mannotriose, mannotetraose, and mannopentaose from galactose-free β-mannan, with mannotriose being the predominant reaction product. The catalytic efficiency (k /K ) of AoMan134A was 6.8-fold higher toward galactomannan from locust bean gum, than toward galactomannan from guar gum, but similar toward galactomannan from locust bean gum and glucomannan from konjac flour. After incubation at 70°C for 120 min, the activity of AoMan134A toward glucomannan decreased to 50% of the maximal activity at 30°C. AoMan134A retained 50% of its β-1,4-mannanase activity after heating at 90°C for 30 min, indicating that AoMan134A is thermostable. Furthermore, AoMan134A was stable within a neutral-to-alkaline pH range, as well as exhibiting stability in the presence of a range of organic solvents, detergents, and metal ions. These findings suggest that AoMan134A could be useful in a diverse range of industries where conversion of β-mannans is of prime importance.