Abstract
Laccases can catalyze the remediation of hazardous synthetic dyes in an eco-friendly manner, and thermostable laccases are advantageous to treat high-temperature dyeing wastewater. A novel laccase from Geothermobacter hydrogeniphilus (Ghlac) was cloned and expressed in Escherichia coli. Ghlac containing 263 residues was characterized as a functional laccase of the DUF152 family. By structural and biochemical analyses, the conserved residues H78, C119, and H136 were identified to bind with one copper atom to fulfill the laccase activity. In order to make it more suitable for industrial use, Ghlac variant Mut2 with enhanced thermostability was designed. The half-lives of Mut2 at 50 °C and 60 °C were 80.6 h and 9.8 h, respectively. Mut2 was stable at pH values ranging from 4.0 to 8.0 and showed a high tolerance for organic solvents such as ethanol, acetone, and dimethyl sulfoxide. In addition, Mut2 decolorized approximately 100% of 100 mg/L of malachite green dye in 3 h at 70 °C. Furthermore, Mut2 eliminated the toxicity of malachite green to bacteria and Zea mays. In summary, the thermostable laccase Ghlac Mut2 could effectively decolorize and detoxify malachite green at high temperatures, showing great potential to remediate the dyeing wastewater.
Highlights
Published: 29 October 2021Laccases, a member of polyphenol oxidases, can oxidize a wide range of phenolic and nonphenolic compounds [1].Laccases typically contain four copper atoms in their active center [1]
The open reading frame of Ghlac encoding an uncharacterized protein containing the consensus sequences of DUF152 laccases was found in the thermophile G. hydrogeniphilus
The structure model indicated that Ghlac has a similar structural fold to the DUF152 member GsYlmD (Figure 1B)
Summary
Published: 29 October 2021Laccases (benzenediol: oxygen oxidoreductase, EC 1.10.3.2), a member of polyphenol oxidases, can oxidize a wide range of phenolic and nonphenolic compounds [1].Laccases typically contain four copper atoms in their active center [1]. During the subsequent electron transferring, oxygen is reduced to water at the trinuclear center formed by Type 2 and 3 copper [2]. Thanks to their broad substrate specificity and the green reaction only requiring oxygen and releasing water as the sole by-product, laccases have been applied for industrial use such as delignification to improve biomass saccharification [3], biobleaching [4], degradation of environmental pollutants [5], and decolorization and detoxification of dyes [6,7]. The long production cycle, poor thermostability, and low tolerance for the alkaline condition hinder the practical application of fungal
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