Description

Fungal ligninases, or lignin peroxidases (LiPs), and manganese-dependent peroxidases (MnPs), are extracellular haem enzymes involved in the degradation of lignin. Lignin is the second most abundant organic compound on Earth and its biodegradation is slow. Certain fungi are able extensively to decompose all the important structural components of wood, including both cellulose and lignin.The first step in lignin degradation is depolymerisation, catalysed by the LiPs (ligninases). LiPs are secreted, along with hydrogen peroxide (H₂O₂), by white-rot fungi under conditions of nutrient limitation. 3D structures have been determined for LiP and MnP from Phanerochaete chrysosporium (White-rot fungus), and for the fungal peroxidase from Arthromyces ramosus. All these proteins share the same architecture and consist of 2 all-alpha domains, between which is embedded the haem group. The helical topography of LiPs is nearly identical to that of yeast CcP. Class II peroxidases (unlike Class I and like Class III) are glycosylated and contain calcium ions and disulfide bridges as well as a peptide signal directing the protein to the endoplasmic reticulum for secretion.
Lignin Peroxidase (LiP, EC 1.11.1.14): LiP attacks lignin bonds directly. Contains a W residu conserved.
Manganese Peroxidase (MnP, EC 1.11.1.13): In MnP, Mn²⁺ serves as the reducing substrate. MnP takes an electron from Mn(II), resulting in Mn(III) that diffuses from the enzyme surface and attacks lignin. Keys residus for Mn oxidation (ExxxE and D).
Versatile Peroxidase (VP): Multifunctional peroxidases sharing the catalytic properties of LiP and MnP. The protein sequences present keys residus for Mn oxidation (ExxxE and D) as well as the conserved W.
Ancestral Lignin Peroxidase (CII): Protein sequences found at the origin of the "lignin tree". Keys residus for Mn oxidation (ExxxE and D) as well as the conserved W are missing. The sequences have a shorter C-Term.
New CII Peroxidase (CII): Proteins mainly present in Ascomycota (plant pathogen). Keys residus for Mn oxidation (ExxxE and D) as well as the conserved W are missing. Also referred as "generic peroxidases" in Floudas et al. 2012 FOLy (Fungal Oxidative Lignin enzYme) a database that describes oxidases potentially involved in the degradation of lignin and including class II peroxidases can bring complementary information.