Expanding the laccase-toolbox: A laccase from Corynebacterium glutamicum with phenol coupling and cuprous oxidase activity

• New laccase CgL1 from Corynebacterium glutamicum was expressed in E. coli.
• CgL1 is stable in the presence of organic solvents and at elevated temperatures.
• CgL1 is active at alkaline pH-values.
• CC / C-O coupling of phenolic acids as well as oxidation of Cu+ with CgL1 was demonstrated.
• Dehydrodimer of sinapic acid is the main product of sinapic acid conversion.

Laccases are oxidases with potential for application in biotechnology. Up to now only fungal laccases have been applied in technical processes, although bacterial laccases are generally easier to handle and more stable at alkaline pH values and elevated temperatures. To increase the toolbox of bacterial laccases and to broaden our knowledge about them, new enzymes have to be characterized. Within this study, we describe the new bacterial laccase CgL1 from Corynebacterium glutamicum. CgL1 was found to oxidize typical laccase substrates like 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid), syringaldazine and 2,6-dimethoxyphenol. The enzyme also demonstrates cuprous oxidase activity. Furthermore, CgL1 is active for several hours at temperatures up to 60 °C and at alkaline pH, as well as stable in different organic solvents. This makes CgL1 a potential candidate for technical applications. In addition, CgL1 was found to catalyze the CC/CO coupling of several phenolic compounds which can serve as precursors for the synthesis of natural products like antibiotics and phytohormones. This activity and product distribution were influenced by pH value and mediators used.

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