Evidence implicating a novel thiol methyltransferase in the detoxification of glucosinolate hydrolysis products in Brassica oleracea L.

Abstract

The physiological relevance of a novel thiol methyltransferase from cabbage, and its possible role in sulphur metabolism have been investigated. The enzyme was absent from the chloroplast, the site of sulphate reduction, and was localized in the cytosol. Potential substrates were initially screened on the basis of their ability to inhibit the methylation of iodide, a previously known substrate for the enzyme. Thiocyanate, 4,4¢-thiobisbenzenethiol, thiophenol, and thiosalicylic acid were identified as possible substrates. Methylation of these thiols by the purified enzyme using [Methyl-3 H]S-adenosyl-L-methionine confirmed their nature as substrates. The purified enzyme strongly preferred thiocyanate as a methyl acceptor. The enzyme had K m values of 11, 51, 250 and 746 mmol m -3 for thiocyanate, 4,4¢-thiobisbenzenethiol, thiophenol and thiosalicylic acid, respectively. The identity of methylthiocyanate as the product of thiocyanate methylation by the purified enzyme was confirmed by mass spectrometry. The enzyme was strictly associated with glucosinolate-containing plants. Thiol substrates of the enzyme are known products of glucosinolate hydrolysis. Our observations indicate that this enzyme could be involved in the detoxification of reactive thiols produced upon glucosinolate degradation in these plants.

Quantitative proteomics reveals the mechanism and consequence of gliotoxin-mediated dysregulation of the methionine cycle in Aspergillus niger

“…It thus appears that mono-methylation by MT-II is a much faster reaction compared to bis-thiomethylation and that this subsequent activity results in a progressive incorporation of methyl groups [11]. In plants, the biological function of thiol methyltransferases (TMTs) has been associated with the detoxification of xenobiotics, for example: reactive thiols produced during the degradation of glucosinolate in cabbage, like thiocyanate and thiosalicylic acid, are detoxified by a TMT that thiomethylates them into non-reactive derivatives [42]. The same role was observed in Phycomitrella patens, whereby PpSABATH1 was responsible for the detoxification of thiobenzoic acid [43].…”

Characterization of three halide methyltransferases in Arabidopsis thaliana

“…It was reported that methyl chloride transferase (MCT) from Batis maritima (Wuosmaa and Hager 1990;Ni and Hager 1998) and thiol methyltransferases (TMT) from Brassica oleracea (Attieh et al 2000a;Attieh et al 2000b;Attieh et al 2002) possess S-adenosyl-L-methionine (SAM)-dependent methyltransferase activities and could synthesize methyl halide in vitro (Attieh et al 2000a;Wousmaa and Hager 1990). The hypotheses concerning the physiological meaning of these enzymes include their involvement in salt tolerance (Ni and Hager 1999) or in metabolizing glucosinolate hydrolysis products such as thiols and thiocyanate (Attieh et al 2000a).…”

“…The hypotheses concerning the physiological meaning of these enzymes include their involvement in salt tolerance (Ni and Hager 1999) or in metabolizing glucosinolate hydrolysis products such as thiols and thiocyanate (Attieh et al 2000a). The AtHOL1 gene was isolated from Arabidopsis as the MCT homolog, and the T-DNA insertion mutant analyses revealed that AtHOL1 was involved in the synthesis of methyl halides including methyl chloride, methyl bromide, and methyl iodide (Rhew et al 2003).…”

A Study on the Production and Emission of Marine-Derived Volatile Halocarbons

“…Homologues of this enzyme have been found in several organisms, such as higher plants (Attieh et al 2000;Itoh et al 2009), algae (Itoh et al 1997), fungi, and soil bacteria (Amachi et al 2001) In this study, various marine phytoplankton were cultivated in order to clarify the molecular formation mechanism of methyl halides and to establish a correlation between intracellular halide ion methyl transferase/halide ion thiol methyl transferase (HTM/HTMT) activity and CH 3 X emission. The enzyme genes were isolated from marine phytoplankton, verified, expressed in E. coli, and characterized in detail.…”