Specificity enhancement towards phenolic substrate by immobilization of laccase on surface plasmon resonance sensor chip

• Laccases are polyphenol oxidases that exhibit broad substrate specificity.
• A laccase from Bacillus sp. HR03 was immobilized on the carboxymethyl dextran chip.
• The immobilization of laccase altered its substrate specificity toward phenolic substrate.
• Atomic force microscopy revealed a uniform distribution of laccase over the sensor surface.
• The results could lead to the utility of laccase in developing a specific phenolic biosensor.

In the modern biomedical and environmental technology, development of high performance sensing methods for phenolic compound is a critical issue because of its potential toxicity for human and environment. Laccases are polyphenol oxidases that exhibit broad substrate specificity; they act on both phenolic and non-phenolic compounds. Constructing a selective, sensitive and fast phenolic detecting system is a challenge for modern technologies. In the present study a laccase from Bacillus sp. HR03 was immobilized on the carboxymethyl dextran chip that altered its substrate specificity toward phenolic substrate. Since the opposite side of active site was enrich of Lys, oriented attachment via amine coupling was expected. Atomic force microscopy revealed a uniform distribution of the enzyme over the sensor surface. Surface plasmon resonance demonstrated no interactions toward non phenolic substrate (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)) and HPLC analysis of the reaction products revealed no peak. Significant conformational changes of the free enzyme toward non-phenolic substrate were detected using fluorescence spectroscopy. Therefore, the inactivation of immobilized enzyme toward non phenolic substrate was due to rigidification. The results of the current study could lead to the utility of laccase in developing a sensitive and specific catalytic detection system of phenolic compound based on surface plasmon resonance.

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