Properties of a beta-D-mannosidase from Aspergillus niger

Area of Science:

• Enzymology
• Biochemistry
• Microbial Biotechnology

Background:

• Beta-D-mannosidase (EC 3.2.1.25) is a key enzyme involved in mannose metabolism.
• Understanding its properties is crucial for biotechnological applications.
• Aspergillus niger is a known source of industrially relevant enzymes.

Purpose of the Study:

• To purify and characterize beta-D-mannosidase from Aspergillus niger.
• To determine the enzyme's kinetic and structural properties.
• To assess its heat stability and specificity.

Main Methods:

• Purification using ammonium sulfate fractionation, DEAE-cellulose chromatography, and affinity chromatography.
• Homogeneity assessment and molecular weight determination.
• Enzyme activity assays, isoelectric focusing, amino acid analysis, and secondary structure analysis.

Main Results:

• Highly purified, homogeneous beta-D-mannosidase (188 units/mg) was obtained.
• The enzyme has a molecular weight of 130,000 ± 5,000 Da and an isoelectric point of 4.7.
• Optimal activity observed at pH 3.5 and 55°C, with significant heat stability (2 hours at 55°C) attributed to beta-sheet structure and glycosylation.

Conclusions:

• The purified Aspergillus niger beta-D-mannosidase is a stable enzyme with potential applications.
• Its structural features, including high beta-sheet content and glycosylation, contribute to its heat stability.
• Mannose competitively inhibits the enzyme, indicating substrate specificity.