Biochemical Characterization of a Novel Endo-1,5-α-L-arabinanase from Rhizomucor miehei

A novel gene (designated as RmArase) encoding endo-1,5-alpha-l-arabinanase from a thermophilic fungus Rhizomucor miehei was cloned and expressed in Escherichia coli. The gene had an open reading frame (ORF) of 930 base pairs (bp) encoding 309 amino acids. The amino acid sequence shared highest identity (56%) with a glycoside hydrolase (GH) family 43 endo-1,5-alpha-l-arabinase from Bacillus subtilis and low identity (35%) with the endo-1,5-alpha-l-arabinase from Aspergillus niger. The recombinant endo-1,5-alpha-l-arabinase (RmArase) was purified to homogeneity with a molecular mass of 40.6 kDa. The purified enzyme had a specific activity of 109 units/mg. The optimal temperature and pH of RmArase were determined to be 55 degrees C and 5.5, respectively. It was stable up to 45 degrees C and within pH 5.0-8.5. The Km values of RmArase toward debranched arabinan and sugar beet arabinan were 5.8 and 27.5 mg/mL, respectively. RmArase efficiently degraded arabinans to yield and arabinobiose and arabinose as major end products, which was different from most other endo-1,5-alpha-l-arabinases. The synergistic action of RmArase and the pectinase could significantly improve the degradation of sugar beet pulp. These properties make RmArase useful in several industries.