Lignin peroxidase active-site structure

Fig. 4. Active-site structure of lignin peroxidase. The dashed lines represent H-honds between N1 of the distal His47 and the side-chain carbonyl of Asn84, and N1 of the proximal Hisl76 and the side-chain carboxylate of Asp238. This diagram was generated using the X-ray coordinates for the 2.0-A structure of LIP (5).

Lignin peroxidase, secreted by the white-rot fungus Phanerochaete chrysosporium in response to nutrient deprivation, catalyzes the H202-dependent oxidation of non-phenolic aromatic substrates. The present report summarizes the kinetic and structural characteristics of lignin peroxidase isozymes. Our results indicate that the active site of lignin peroxidase is more electron deficient than other peroxidases. As a result, the redox potential of the heme active site is higher, the heme active site is more reactive and the oxycomplex is more stable than that of other peroxidases. Also discussed is the heme-linked ionization of lignin peroxidase. 

However, the distal histidine apparently has no effect on lignin and Mn-dependent peroxidase compound I formation. Although all active site amino acid residues that are proposed to participate in compound I formation of peroxidase (37) are conserved in lignin and Mn-dependent pa oxidases, the lack of pH dependence may be a result of some inherent structural and conformational differences between lignin and Mn-dependent peroxidases and other peroxidases. 

Manganese peroxidase (MnP) is an unique enzyme in many respects. It is an extracellular enzyme that involves a heme protoporphyrin IX for the oxidation of Mn" to Mn " 94, 95). A crystal structure at 2.06-A resolution of the manganese peroxidase from the white rot basidiomycete Phanerocaete chrysosporium, which utilizes this enzyme to degrade lignin, appeared in 1994 96). The active site (Fig. 5) and the overall structure are quite similar to lignin peroxidase (LiP),... 

Peroxidases (EC number 1.11.1.x) are a large family of enzymes reducing hydrogen peroxide or organic hydroperoxides to water or alcohols respectively. Most peroxidases are structurally similar to cytochrome c peroxidase (CCP), as for example horseradish peroxidase (HRP) and lignin peroxidase (LiP). Active sites contain usually a heme factor or redox-active cysteine or selenocysteine residues. The general reaction in these enzymes can be written as... 

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