Regulatory Factors Associated with Synthesis of the Osmolyte Glycine Betaine in the Halophilic Methanoarchaeon Methanohalophilus portucalensis

Abstract

The halophilic methanoarchaeon Methanohalophilus portucalensis can synthesize de novo and accumulate β-glutamine, N ɛ-acetyl-β-lysine, and glycine betaine (betaine) as compatible solutes (osmolytes) when grown at elevated salt concentrations. Both in vivo and in vitro betaine formation assays in this study confirmed previous nuclear magnetic resonance 13C-labelling studies showing that the de novo synthesis of betaine proceeded from glycine, sarcosine, and dimethylglycine to form betaine through threefold methylation. Exogenous sarcosine (1 mM) effectively suppressed the intracellular accumulation of betaine, and a higher level of sarcosine accumulation was accompanied by a lower level of betaine synthesis. Exogenous dimethylglycine has an effect similar to that of betaine addition, which increased the intracellular pool of betaine and suppressed the levels of N ɛ-acetyl-β-lysine and β-glutamine. Both in vivo and in vitro betaine formation assays with glycine as the substrate showed only sarcosine and betaine, but no dimethylglycine. Dimethylglycine was detected only when it was added as a substrate in in vitro assays. A high level of potassium (400 mM and above) was necessary for betaine formation in vitro. Interestingly, no methylamines were detected without the addition of KCl. Also, high levels of NaCl and LiCl (800 mM) favored sarcosine accumulation, while a lower level (400 mM) favored betaine synthesis. The above observations indicate that a high sarcosine level suppressed multiple methylation while dimethylglycine was rapidly converted to betaine. Also, high levels of potassium led to greater amounts of betaine, while lower levels of potassium led to greater amounts of sarcosine. This finding suggests that the intracellular levels of both sarcosine and potassium are associated with the regulation of betaine synthesis inM. portucalensis.

Osmoadaptation in Archaea

“…More importantly, in vitro studies show that the methylation reactions are K ϩ dependent, with little betaine accumulating below 0.4 M K ϩ ; at this potassium concentration sarcosine was the major product. K ϩ concentrations above 0.4 M enhanced GB synthesis from sarcosine and N,N-dimethylglycine (37). This observation suggests that control of betaine synthesis is modulated by intracellular K ϩ ; this cation may also function as an intracellular signal for osmoregulation in M. portucalensis.…”

“…Methanohalophilus portucalensis is relatively unique in the archaeal domain in that it can synthesize GB de novo (36). The biosynthesis of GB in this organism occurs by methylation of glycine (56) with S-adenosylmethionine as the methyl donor (37). More importantly, in vitro studies show that the methylation reactions are K ϩ dependent, with little betaine accumulating below 0.4 M K ϩ ; at this potassium concentration sarcosine was the major product.…”

Glycine N‐methyltransferase is a favorable prognostic marker for human cholangiocarcinoma

“…7 In this study, we observed the presence of GNMT in cholangiocytes, which are also responsible for digestive enzyme secretion. Previously, Lai et al 15 reported that GNMT plays a major role in osmoregulation in halophilic methanoarchaea, suggesting GNMT involvement in regulating the secretory function of cells. It is noteworthy that the GNMT expression pattern in cholangiocarcinoma tissues differs from that seen in normal bile ducts (Fig.…”

Induction of xylem sap methylglycine by a drought and rewatering treatment and its inhibitory effects on the growth and development of plant organs

“…We focused on an amino acid, methylglycine (MeGly sarcosine), in Cucurbita maxima xylem sap collected from roots. MeGly has previously been detected in low amounts in plant tissues and is an intermediate in the synthesis of betaine [trimethylglycine (TMG)] which acts as an osmoprotectant (Chen and Murata 2002, Lai et al 1999, Withers and Guppy 1996. The presence of MeGly in xylem sap and the physiological effects of MeGly on plant growth and development have never been reported before.…”