Secretory expression and characterization of a soluble laccase from the Ganoderma lucidum strain 7071-9 in Pichia pastoris

Abstract

Laccases are strong oxidizing enzymes that oxidize chlorinated phenols, synthetic dyes, pesticides, polycyclic aromatic hydrocarbons as well as a very wide range of other compounds with high redox potential. Based on the bias of genetic codons between fungus and yeast, we synthesized a laccase gene GlLCCI, originated from Ganoderma lucidum using optimized codons and a PCR-based two-step DNA synthesis method. The recombinant laccase, GlLCCI was successfully over-expressed in yeast, Pichia pastoris, with an alcohol oxidase1 promoter. The recombinant GlLCCI has a molecular mass of approximately 58kDa. The K (m) values of GlLCCI for 2-2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and guaiacol were 0.9665, and 1.1122mM, respectively. The V (max) of GlLCCI for both substrates was 3,024 and 82.13μMmg(-1)min(-1). When ABTS was used as a substrate, the enzyme had an optimal temperature of approximately 55°C. The enzyme was detected over pH values from 2 to 8. The enzyme was strongly activated by K(+), Na(+), Cu(2+) and mannitol. Six amino acids (alanine, histidine, glycine, arginine, aspartate and phenylalanine) increased the catalytic ability of the enzyme. The activity of laccase was obviously inhibited by Fe(2+), Fe(3+), sodium hydrosulphite, and sodium azide. Additionally, under optimal conditions, GlLCCI decolorized 37.62mgl(-1) of azo dye methyl orange (MO) in cultural medium. With a high MO degradation ability, GlLCCI may have potential in the treatment of industrial effluent containing azo dye MO.