Enzymatic properties and modification of sucrose phosphorylase from the metagenome of sucrose-enriched environment

Abstract:

[Background] The metagenome of sucrose-enriched soil is one of the important sources of sucrose phosphorylase. The enzyme has important applications in industries, as it can catalyze transglycosylation reaction to improve the properties of the receptors using cheap sucrose. [Objective] The properties and transglycosylation activity of sucrose phosphorylase isolated from the metagenome were studied, providing foundation and research materials for better modification. [Methods] A gene encoding sucrose phosphorylase from metagenomic library was cloned into the expression vector pSE380, and the recombinant strain was constructed. Then, the target protein was purified by nickel affinity chromatography. The properties were determined using sucrose as substrate, and transglycosylation activities of the carbohydrate receptors were also investigated. After protein modeling and substrate channel were analyzed, the site-saturation mutagenesis at the amino acid 155 was performed by reverse PCR. The enzymatic properties and transglycosylation activity of the mutants also were studied in detail. [Results] The molecular weight of purified protein is about 56 kD. And the recombinant protein exists in the form of a trimer in the active state. The optimum temperature and pH value were 55 °C and 6.5, respectively; Km and Vmax value were 23.1±2.4 mmol/L and 407.9±8.5 μmol/(mg·min) using sucrose as substrate. Among the site-directed saturation mutants of the amino acid 155, some mutants showed improved enzymatic properties or transglycosylation activities. [Conclusion] The study of sucrose phosphorylase from the metagenomics enriched the enzymatic data. The mutants with better properties were obtained, which provides theoretical foundation for researching on key amino acids related to transglycosylation and the applications of sucrose phosphorylase.