Agaricales Mushroom Lignin Peroxidase: From Structure-Function to Degradative Capabilities.

Area of Science:

• Biochemistry
• Enzymology
• Fungal Biotechnology

Background:

• Lignin biodegradation is crucial for nutrient cycling and biofuel production.
• White-rot fungi, primarily from the Polyporales order, are known for secreting efficient lignin-degrading enzymes called lignin peroxidases (LiPs).
• The order Agaricales, with numerous species, has been less explored for such enzymes.

Purpose of the Study:

• To characterize a novel lignin peroxidase (ApeLiP) from the soil-inhabiting fungus Agrocybe pediades (order Agaricales).
• To elucidate the structural and biochemical properties of ApeLiP and compare it to known LiPs.
• To investigate the role of a specific tryptophan residue in ApeLiP's catalytic activity and substrate oxidation.

Main Methods:

• X-ray crystallography for structural analysis.
• Biochemical assays to determine substrate oxidation capabilities (lignin model compounds, dyes, real lignin).
• Stopped-flow rapid spectrophotometry and 2D-NMR for mechanistic studies and reduction potential estimation.
• Site-directed mutagenesis to create and analyze a tryptophan-deficient variant.

Main Results:

• ApeLiP is structurally similar to Polyporales LiPs, featuring a conserved heme-pocket and a solvent-exposed tryptophan.
• ApeLiP efficiently oxidizes phenolic and non-phenolic lignin model compounds, various dyes, and actual lignin.
• The solvent-exposed tryptophan is identified as the oxidation site for lignin and high redox-potential substrates, and plays a role in phenolic substrate oxidation.
• ApeLiP exhibits broad pH stability (acidic to basic) with different optimal pHs for phenolic and non-phenolic compound oxidation.
• Reduction potentials indicate similar H2O2 activation but lower compound-II reduction potential compared to other LiPs.

Conclusions:

• ApeLiP represents a novel lignin peroxidase from the Agaricales order with significant potential for lignin biodegradation.
• Its unique structural and biochemical properties, including broad pH stability and specific oxidation mechanisms, make it a promising candidate for industrial applications.
• The identified tryptophan residue is critical for ApeLiP's catalytic function, offering insights into enzyme engineering for enhanced lignin degradation.