Characterization of a laccase from a wood‐feeding termite, Coptotermes formosanus

Abstract

Coptotermes formosanus Shiraki is a wood-feeding termite which secretes a series of lignolytic and cellulolytic enzymes for woody biomass degradation. However, the lignin modification mechanism in the termite is largely elusive, and the characteristics of most lignolytic enzymes in termites remain unknown. In this study, a laccase gene lac1 from C. formosanus was heterogeneously expressed in insect Sf9 cells. The purified Lac1 showed strong activities toward hydroquinone (305 mU/mg) and 2,6-dimethoxyphenol (2.9 mU/mg) with low K values, but not veratryl alcohol or 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid). Lac1 could function well from pH 4.5 to 7.5, and its activity was significantly inhibited by H O at above 4.85 mmol/L (P < 0.01). In addition, the lac1 gene was found to be mainly expressed in the salivary glands and foregut of C. formosanus, and seldom in the midgut or hindgut. These findings suggested that Lac1 is a phenol-oxidizing laccase like RflacA and RflacB from termite Reticulitermes flavipes, except that Lac1 was found to be more efficient in phenol oxidation, and it did not require H O for its function. It is suspected that this kind of termite laccase might only be able to directly oxidize low redox-potential substrates, and the high redox-potential groups in lignin might be oxidized by other enzymes in the termite or by using the Fenton reaction.

Transcriptome analysis of the digestive system of a wood-feeding termite (Coptotermes formosanus) revealed a unique mechanism for effective biomass degradation

“…Specifically, a homogenous AA1 laccase from termite Reticulitermes flavipes has been proven to modify lignin alkali [ 14 ], and such AA1 laccases were deduced to be a kind of biological pretreatment enzymes. In our previous work, Hemo1 [ 28 ] and recombinant Lac1 [ 15 ], both from C. formosanus , have been proved to oxidize ABTS [2,2′-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)] or hydroquinone, respectively, and they were very likely involved in lignin modification in termite gut system.…”

“…However, the key auxiliary redox enzymes [ 13 ] involved in the oxidative modification process are still yet to be found systematically. Even though some enzyme studies mainly focus on laccase and peroxidase for lignin degradation [ 14 , 15 ], most of the “omics” works only focus on the glycosyl hydrolases involved in cellulolytic functions, despite the importance of the auxiliary redox enzymes involved in lignin modification [ 16 – 19 ].…”

Laccases: structure, function, and potential application in water bioremediation

“…Three-domain laccases are mainly studied in fungi, but have also been observed in some bacteria, archaea, plants, and insects [22, 146]. The database containing information on different laccases and MCOs is BioCatNet [147].…”

Laccase Immobilized onto Zirconia–Silica Hybrid Doped with Cu2+ as an Effective Biocatalytic System for Decolorization of Dyes

“…Laccases are oxidoreductases which catalyse the oxidation of a wide variety of organic compounds, including mono-, di- and polyphenols as well as aliphatic and aromatic amines [1]. These enzymes are widespread in nature and most commonly extracted from white or red rot fungi, such as Trametes versicolor or Trametes vilosa [2]. Four adjacent copper atoms are located at the active sites of laccase which correspond to the blue color to the enzyme molecule, hence the protein is often called “blue oxidase”.…”