Abstract
Trametes hirsuta is able to secrete laccase isoenzymes including constitutive and inducible forms, and has potential application for bioremediation of environmental pollutants. Here, an inducible group B laccase from T. hirsuta MX2 was heterologously expressed in Pichia pastoris, and its yield reached 2.59 U/mL after 5 days of methanol inducing culture. The optimal pH and temperature of recombinant laccase (rLac1) to 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) were 2.5 and 60 °C, respectively. Metal ions showed different effect on rLac1 which Mg2+, Cu2+, and K+ increased enzyme activity as their concentration increased, whereas Zn2+, Na+, and Fe2+ inhibited enzyme activity as their concentration increased. rLac1 showed good tolerance to organic solvents, and more than 42% of its initial activity remained in 10% organic solvents. Additionally, rLac1 exhibited a more efficient decolorization ability for remazol brilliant blue R (RBBR) than for acid red 1 (AR1), crystal violet (CV), and neutral red (NR). Molecular docking results showed RBBR has a stronger binding affinity with laccase than other dyes by interacting with substrate binding cavity of enzyme. The results indicated rLac1 may be a potential candidate for dye removal from textile wastewater.
Highlights
Azo, heterocycle, and triphenylmethane are widely used in textile, tannery and printing, cosmetic, paper, and pharmaceutical industries [1]
The Lac1 was ligated into pPIC9K to generate expression vector pPIC9K-Lac1, which was integrated into the P. pastoris genome by electroporation
In MD screening medium, forty yeast recombinants were randomly selected for detection of laccase activity in a 96-well plate (Figure 1a)
Summary
Azo, heterocycle, and triphenylmethane are widely used in textile, tannery and printing, cosmetic, paper, and pharmaceutical industries [1]. The removal of dyes by adsorption, coagulation, ozonation, and chemical degradation is often high-cost and can generate hazardous by-products [6]. Biodegradation of synthetic dyes by enzymes has attracted increasing attention in recent years because its advantage of high efficiency and eco-friendly procedures in the treatment of dye effluent [7–9]. In laccase-mediated catalytic reaction, water is the sole by-product produced by the transfer of electrons from hydrogen donating substrate to molecular oxygen. The extensive substrates and unique catalytic mechanism of laccase make it application in agricultural, industrial, medicinal, and environmental areas [11]. More and more laccases have been proved to be the enzymes with great potential in the degradation of synthetic dyes [9,12,13].
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