title: Identification of phosphomethylethanolamine N-methyltransferase from Arabidopsis and its role in choline and phospholipid metabolism.
abstract: 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.
authors.affiliation: Department of Biology, McMaster University, Hamilton, Ontario L8S 4A8, Canada.
authors.forename: Michael D
authors.initials: MD
authors.lastname: BeGora
authors.forename: Mitchell J R
authors.initials: MJ
authors.lastname: Macleod
authors.forename: Brian E
authors.initials: BE
authors.lastname: McCarry
authors.forename: Peter S
authors.initials: PS
authors.lastname: Summers
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Weretilnyk
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002794:Choline / Q000378:metabolism*; D005816:Genetic Complementation Test; D010713:Phosphatidylcholines / Q000378:metabolism; D050918:Phosphatidylethanolamine N-Methyltransferase / Q000235:genetics / Q000378:metabolism*; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010743:Phospholipids; D050918:Phosphatidylethanolamine N-Methyltransferase; D002794:Choline