Cloning and Functional Expression of an Acidophilic β-Mannanase Gene (Anman5A) from Aspergillus niger LW-1 in Pichia pastoris

A cDNA fragment of the Anman5A, a gene that encodes an acidophilic β-mannanase of Aspergillus niger LW-1 (abbreviated as AnMan5A), was cloned and functionally expressed in Pichia pastoris . Homology alignment of amino acid sequences verified that the AnMan5A belongs to the glycoside hydrolase (GH) family 5. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) assay demonstrated that the recombinant AnMan5A (reAnMan5A), a N-glycosylated protein with an apparent molecular weight of 52.0 kDa, was secreted into the medium. The highest reAnMan5A activity expressed by one P. pastoris transformant, labeled as GSAnMan4-12, reached 29.0 units/mL. The purified reAnMan5A displayed the highest activity at pH 3.5 and 70 °C. It was stable at a pH range of 3.0-7.0 and at a temperature of 60 °C or below. Its activity was not significantly affected by an array of metal ions and ethylenediaminetetraacetic acid (EDTA). The K(m) and V(max) of the reAnMan5A, toward locust bean gum, were 1.10 mg/mL and 266.7 units/mg, respectively.