title: Plants synthesize ethanolamine by direct decarboxylation of serine using a pyridoxal phosphate enzyme.
abstract: The established pathways from serine to ethanolamine are indirect and involve decarboxylation of phosphatidylserine. Here we show that plants can decarboxylate serine directly. Using a radioassay based on ethanolamine (Etn) formation, pyridoxal 5'-phosphate-dependent l-serine decarboxylase (SDC) activity was readily detected in soluble extracts from leaves of diverse species, including spinach, Arabidopsis, and rapeseed. A putative Arabidopsis SDC cDNA was identified by searching GenBank for sequences homologous to other amino acid decarboxylases and shown by expression in Escherichia coli to encode a soluble protein with SDC activity. This cDNA was further authenticated by complementing the Etn requirement of a yeast psd1 psd2 mutant. In a parallel approach, a cDNA was isolated from a rapeseed library by its ability to complement the Etn requirement of a yeast cho1 mutant and shown by expression in E. coli to specify SDC. The deduced Arabidopsis and rapeseed SDC polypeptides are 90% identical, lack obvious targeting signals, and belong to amino acid decarboxylase group II. Recombinant Arabidopsis SDC was shown to exist as a tetramer and to contain pyridoxal 5'-phosphate. It does not attack d-serine, l-phosphoserine, other l-amino acids, or phosphatidylserine and is not inhibited by Etn, choline, or their phosphoesters. As a soluble, pyridoxal 5'-phosphate enzyme, SDC contrasts sharply with phosphatidylserine decarboxylases, which are membrane proteins that have a pyruvoyl cofactor.
authors.affiliation: Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611, USA.
authors.forename: D
authors.initials: D
authors.lastname: Rontein
authors.forename: I
authors.initials: I
authors.lastname: Nishida
authors.forename: G
authors.initials: G
authors.lastname: Tashiro
authors.forename: K
authors.initials: K
authors.lastname: Yoshioka
authors.forename: W I
authors.initials: WI
authors.lastname: Wu
authors.forename: D R
authors.initials: DR
authors.lastname: Voelker
authors.forename: G
authors.initials: G
authors.lastname: Basset
authors.forename: A D
authors.initials: AD
authors.lastname: Hanson
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism*; D002262:Carboxy-Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D018076:DNA, Complementary; D019856:Ethanolamine / Q000378:metabolism*; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000201:enzymology / Q000378:metabolism; D011732:Pyridoxal Phosphate / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism*
chemical_list: D018076:DNA, Complementary; D011994:Recombinant Proteins; D012694:Serine; D019856:Ethanolamine; D011732:Pyridoxal Phosphate; D002262:Carboxy-Lyases; C437332:L-serine decarboxylase