Direct interaction of lignin and lignin peroxidase from basidiomycete phanerochaete chrysosporium

Binding properties of lignin peroxidase (LIP) from the basidiomycete Phanerochaete chrysosporium against a synthetic lignin (DHP) were studied utilizing the resonant mirror biosensor. Among several ligninolytic enzymes, only LiP specifically binds to DHP. Kinetic analysis revealed that the binding occured reversibly, and that the forward reaction obeyed the second order association mechanism. This strongly suggests that LiP possesses a specific binding site for lignin. The LiP-DHP interaction was pH dependent, and the ionization group with pKa of 5.3 was involved in the binding site. A one-electron transfer from DHP to LiP cornpound I was characterized using a stopped-flow technique, showing that the reaction obeyed the conventional second order mechanism. This observation clearly indicated that LiP is capable of oxidizing polymeric lignin directly at the protein surface via a long-range electron transfer process. A close look at the crystal structure of LiP suggested that LiP possesses His 239 as a possible tignin binding site on the protein surface, which is linked to Asp 238. This aspartate residue is hydrogen-bonded to the proximal His 176. This would be a possible electron transfer pathway to oxidize polymeric substrates such ms lignin and ferrocytochrome c.