Heterologous expression, function and structure of amine oxidase derived from Lactiplantibacillus plantarum

Abstract:

[Objective] Biogenic amines (BAs) widely exist in fermented food as a group of potentially harmful substances which can be degraded by amine oxidases. This study aims to explore, the enzymatic properties and amine-degrading abilities of amine oxidases from lactic acid bacteria. [Methods] The recombinant protein of the multicopper oxidase gene SufI in Lactobacillus plantarum was obtained through heterologous expression. After expression condition optimization and purification, the optimal reaction conditions, enzyme stability, amine-reducing ability, spectrum, and structural characteristics of the recombinant protein were investigated. [Results] The recombinant enzymes had the optimal performance at pH 3.5 and 20 ℃. The relative activity of the recombinant enzyme was above 70% within pH 4.0–10.0 and 15–65 ℃. This enzyme showed good stability, and was not affected by inhibitors such as ethanol. In a reaction system containing eight BAs, the recombinant enzyme could degrade 403.23 μg/mL and showed the highest degradation rate of 34.99% (70 μg/mL) for tyramine. In a reaction system containing single BAs, the recombinant enzyme had highest substrate specificity affinity toward tyramine, demonstrating the activity of 18.33 U/mL. The UV-visible scanning spectrum showed that the enzyme had a characteristic absorption peak at 600 nm. According to Fourier transform infrared spectrum, the relative content of alpha helixes, beta sheets, beta turns, and random coils in the secondary structure of amide was 21.52%, 20.72%, 33.80%, and 23.97%, respectively. Homologous modeling predicted that the enzyme possessed three copper-binding domains, which contained histidine, cysteine, methionine, glutamate, and other residues. The structure indicated that the recombinant enzyme belonged to the multicopper oxidase family. [Conclusion] The multicopper oxidase from L. plantarum JB1 showed good aciD-base and thermal stability, and was capable of degrading BAs, especially tyramine. It is expected to be further developed for fermented food and beverages.