Expression and purification of an ArsM-elastin-like polypeptide fusion and its enzymatic properties
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Enzymes could act as a useful tool for environmental bioremediation. Arsenic (As) biomethylation, which can convert highly toxic arsenite [As(III)] into low-toxic volatile trimethylarsine, is considered to be an effective strategy for As removal from contaminated environments. As(III) S-adenosylmethyltransferase (ArsM) is a key enzyme for As methylation; its properties and preparation are crucial for its wide application. Currently, ArsM is usually purified as a His-tag fusion protein restricting widespread use due to high costs. In this study, to greatly reduce the cost and simplify the ArsM preparation process, an Elastin-like polypeptide (ELP) tag was introduced to construct an engineered Escherichia coli (ArsM-ELP). Consequently, a cost-effective and simple non-chromatographic purification approach could be used for ArsM purification. The enzymatic properties of ArsM-ELP were systematically investigated. The results showed that the As methylation rate of purified ArsM-ELP (> 35.49%) was higher than that of E. coli (ArsM-ELP) (> 10.39%) when exposed to 25 μmol/L and 100 μmol/L As(III), respectively. The purified ArsM-ELP was obtained after three round inverse transition cycling treatment in 2.0 mol/L NaCl at 32 °C for 10 min with the yield reaching more than 9.6% of the total protein. The optimal reaction temperature, pH, and time of ArsM-ELP were 30 °C, 7.5 and 30 min, respectively. The enzyme activity was maintained at over 50% at 45 °C for 12 h. The enzyme specific activity was 438.8 ± 2.1 U/μmol. ArsM-ELP had high selectivity for As(III). 2-Mercaptoethanol could promote enzyme activity, whereas SDS, EDTA, Fe2+, and Cu2+ inhibited enzyme activity, and Mg2+, Zn2+, Ca2+, and K+ had no significant effects on it.
KeywordsArsenic As(III) S-adenosylmethionine (SAM) methyltransferase Elastin-like polypeptide tag Rhodopseudomonas palustris
This study was funded by National Marine Public Industry Research (No. 201505026), by Natural Science Foundation of Fujian Province (No. 2018J01049), and by Subsidized Project for Cultivating Postgraduates Innovative Ability in Scientific Research of Huaqiao University.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any study with human participants or animals performed by any of the authors.
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