Identification of Phosphomethylethanolamine N-Methyltransferase from Arabidopsis and Its Role in Choline and Phospholipid Metabolism

• Published in: The Journal of biological chemistry 2010-09, Vol.285 (38), p.29147-29155
• Main Authors: BeGora, Michael D., Macleod, Mitchell J.R., McCarry, Brian E., Summers, Peter S., Weretilnyk, Elizabeth A.
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Choline - metabolism; Functional Complementation; Genetic Complementation Test; Metabolism; Methyltransferase; Phosphatidylcholine; Phosphatidylcholines - metabolism; Phosphatidylethanolamine; Phosphatidylethanolamine N-Methyltransferase - genetics; Phosphatidylethanolamine N-Methyltransferase - metabolism; Phosphatidylethanolamines - metabolism; Phosphoethanolamine; Phospholipid Metabolism; Phospholipids - metabolism; Plant; Plant Biology; Plants, Genetically Modified - enzymology; Plants, Genetically Modified - genetics; Plants, Genetically Modified - metabolism; Saccharomyces cerevisiae; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M110.112151

Three sequential methylations of phosphoethanolamine (PEA) are required for the synthesis of phosphocholine (PCho) in plants. A cDNA encoding an N-methyltransferase that catalyzes the last two methylation steps was cloned from Arabidopsis by heterologous complementation of a Saccharomyces cerevisiae cho2, opi3 mutant. The cDNA encodes phosphomethylethanolamine N-methyltransferase (PMEAMT), a polypeptide of 475 amino acids that is organized as two tandem methyltransferase domains. PMEAMT shows 87% amino acid identity to a related enzyme, phosphoethanolamine N-methyltransferase, an enzyme in plants that catalyzes all three methylations of PEA to PCho. PMEAMT cannot use PEA as a substrate, but assays using phosphomethylethanolamine as a substrate result in both phosphodimethylethanolamine and PCho as products. PMEAMT is inhibited by the reaction products PCho and S-adenosyl-l-homocysteine, a property reported for phosphoethanolamine N-methyltransferase from various plants. An Arabidopsis mutant with a T-DNA insertion associated with locus At1g48600 showed no transcripts encoding PMEAMT. Shotgun lipidomic analyses of leaves of atpmeamt and wild-type plants generated phospholipid profiles showing the content of phosphatidylmethylethanolamine to be altered relative to wild type with the content of a 34:3 lipid molecular species 2-fold higher in mutant plants. In S. cerevisiae, an increase in PtdMEA in membranes is associated with reduced viability. This raises a question regarding the role of PMEAMT in plants and whether it serves to prevent the accumulation of PtdMEA to potentially deleterious levels.