Arsenic methylation by an arsenite S-adenosylmethionine methyltransferase from Spirulina platensis

Abstract

Arsenic-contaminated water is a serious hazard for human health. Plankton plays a critical role in the fate and toxicity of arsenic in water by accumulation and biotransformation.Spirulina platensis (S. platensis), a typical plankton, is often used as a supplement or feed for pharmacy and aquiculture, and may introduce arsenic into the food chain, resulting in a risk to human health. However, there are few studies about how S. platensis biotransforms arsenic. In this study, we investigated arsenic biotransformation by S. platensis. When exposed to arsenite (As(III)), S. platensis accumulated arsenic up to 4.1 mg/kg dry weight.After exposure to As(III), arsenate (As(V)) was the predominant species making up 64% to 86% of the total arsenic. Monomethylarsenate (MMA(V)) and dimethylarsenate (DMA(V)) were also detected. An arsenite S-adenosylmethionine methyltransferase from S. platensis (SpArsM) was identified and characterized. SpArsM showed low identity with other reported ArsM enzymes. The Escherichia coli AW3110 bearing SparsM gene resulted in As(III) methylation and conferring resistance to As(III). The in vitro assay showed that SpArsM exhibited As(III) methylation activity. DMA(V) and a small amount of MMA(V) were detected in the reaction system within 0.5 hr. A truncated SpArsM derivative lacking the last 34 residues still had the ability to methylate As(III). The three single mutants of SpArsM (C59S, C186S, and C238S) abolished the capability of As(III) methylation, suggesting the three cysteine residues are involved in catalysis. We propose that SpArsM is responsible for As methylation and detoxification of As(III) and may contribute to As biogeochemistry.

Spirulina platensisameliorates arsenic-mediated uterine damage and ovarian steroidogenic disorder

“…Methylation of arsenic in association with S-adenosylmethionine involves methyl cobalamin (CH 3 B 12 ) and reduced glutathione for arsenic clearance and detoxification with the involvement of enzymes (Nakamura 2011). Arsenite S-adenosyl methionine methyltransferase was isolated and characterized from spirulina (Guo et al 2016). An in vitro assay system demonstrated the arsenic methylation activity of spirulina (Guo et al 2016).…”

“…Arsenite S-adenosyl methionine methyltransferase was isolated and characterized from spirulina (Guo et al 2016). An in vitro assay system demonstrated the arsenic methylation activity of spirulina (Guo et al 2016). This methylation process is the essential prerequisite for the removal of arsenic.…”

Combined Dietary Action of Spirulina and Probiotics Mitigates Female Reproductive Ailments in Arsenicated Rats

“…Methylation of arsenic in association with S-adenosylmethionine involves methylcobalamin (CH 3 B 12 ) and reduced glutathione for arsenic clearance and detoxification 27 . Arsenite S-adenosyl methionine methyl-transferase was isolated and characterized from spirulina 28 . An In vitro assay system demonstrated the arsenic methylation activity of spirulina 28 .…”

“…Arsenite S-adenosyl methionine methyl-transferase was isolated and characterized from spirulina 28 . An In vitro assay system demonstrated the arsenic methylation activity of spirulina 28 . This methylation process is the essential prerequisite for the removal of arsenic.…”

Determination of different arsenic species in food‐grade spirulina powder by ion chromatography combined with inductively coupled plasma mass spectrometry

“…Therefore, the determination of As species in spirulina samples provided accurate information for evaluating the risk of As intake. Different organic arsenic compounds in spirulina samples from different provinces may be from the As biotransformation of spirulina [27,28] or may be from the microbial mediated As biotransformation in the environmental soil [29].…”