Biological Degradation of Anthroquinone and Azo Dyes by a Novel Laccase from Lentinus sp.

This study identifies a new fungal strain, Lentinus sp., that can produce extracellular forms of laccases with an activity of approximately 58 300 U/L. A purified laccase (designated Icc3) was identified by LC-ESI MS/MS as an N-linkage glycosylated protein. The isolated Icc3 cDNA is composed of 1563 bp encoding for a polypeptide of 521 amino acid residues with 4 putative Cu binding regions. Kinetic analyses revealed that the specific activity, k(cat) K-m, and k(cat)/K-m of Icc3 at pH 2.5 and 70 degrees C with 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) used as a substrate was 2047 U mg(-1), 2017 s(-1), 8.4 mu M, and 240 s(-1) mu M-1 respectively. Lcc3 is stable at pH 6.0-10.0 and has a midpoint temperature (T-m) of 77.1 degrees C. We observed 97% decolorization efficiency on Acid Blue 80, 88% on RBBR, and 61% on Acid Red 37 by Icc3. Structural modeling analysis showed that five, four, and three hydrogen bonds can be formed between Acid Blue 80 and Arg(178), Arg(182), or Asn(358); between RBBR and His(132), Ser(134) or Asp(482); and between Acid Red 37 and Arg(178), respectively. Notably, Lentinus Icc3 efficiently reversed the toxicity of anthraquinone and azo dyes on rice seed germination and decolorized industrial textile effluent, suggesting the enzyme may be valuable for bioremediation.