The quest for lignin depolymerases has been under way for more than thirty years.  The two original candidates, lignin peroxidase and manganese-dependent peroxidase, possess only limited ability to degrade lignin chains: both enzymes are poised between cleaving and (re)polymerizing such macromolecular substrates.  A third candidate, laccase acting through an electron-transfer agent or mediator, faces inevitably similar difficulties.  A fundamentally different kind of problem arises from the strong intermolecular noncovalent forces between lignin substructures; these result in stabilization energies that exceed 7 kcal/mol for each pair of interacting aromatic rings.  Thus, cleavage of lignin macromolecules by lignin depolymerase does not necessarily allow the degraded products to diffuse freely into solution; another protein may be required to facilitate dissociation of the cleaved components from the polymeric lignin domains.  Such sequences of molecular events have now been documented experimentally for a lignin depolymerase with a second protein acting in an auxiliary capacity.

Mechanism of enzyme-catalyzed lignin depolymerization

243rd National Meeting (2012)

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