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Publication Abstract from PubMed

Laccases (EC 1.10.3.2) are multicopper oxidases able to oxidize a range of substrates including phenols, aromatic amines and non-phenolic substrates. In order to investigate the involvement of the small Streptomyces laccases in lignin degradation, we generated acid-precipitable polymeric lignin (APPL) obtained in the presence of wild type Streptomyces coelicolor A3(2) (SCWT) and its laccase-less mutant (SCDeltaLAC) in presence of Miscanthus x giganteus lignocellulose. The results showed that strain SCDeltaLAC was inefficient in degrading lignin compared to strain SCWT, thereby supporting the importance of laccase for lignin degradation by Streptomyces coelicolor A3(2). We also studied the lignin degradation activity of laccases from Streptomyces coelicolor A3(2), Streptomyces lividans TK24, Streptomyces viridosporus T7A and Amycolatopsis sp. 75iv2 using both lignin model compounds and ethanosolv lignin. All four laccases degraded a phenolic model compound (LM-OH), but only able to oxidize a non-phenolic model compound (LM-OMe) in the presence of redox mediators. Their activities are highest at pH 8.0 with a low krel/Kapp for LM-OH, suggesting that the enzymes' natural substrates must be different in shape or chemical nature. Crystal structures of the laccases from Streptomyces viridosporus T7A (SVLAC) and Amycolatopsis sp. 75iv2 (AMLAC) were determined both with and without bound substrate. This is the first report of a crystal structure for any laccase bound to a non-phenolic beta-O-4 lignin model compound. An additional zinc metal binding site in SVLAC was also identified. The ability to oxidize/rearrange ethanosolv lignin further provides evidence for the utility of laccase activity for lignin degradation/modification.

The roles of small laccases from Streptomyces in lignin degradation.,Majumdar S, Lukk T, Solbiati JO, Bauer S, Nair SK, Cronan JE, Gerlt JA Biochemistry. 2014 May 28. PMID:24870309^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.