title: Enzymatic properties and substrate specificity of a bacterial phosphatidylcholine synthase.
abstract: Phosphatidylcholine (PC) is a rare membrane lipid in bacteria, but is crucial for virulence of the plant pathogen Agrobacterium tumefaciens and various other pathogens. Agrobacterium tumefaciens uses two independent PC biosynthesis pathways. One is dependent on the integral membrane protein PC synthase (Pcs), which catalyzes the conversion of cytidine diphosphate-diacylglycerol (CDP-DAG) and choline to PC, thereby releasing a cytidine monophosphate (CMP). Here, we show that Pcs consists of eight transmembrane segments with its N- and C-termini located in the cytoplasm. A cytoplasmic loop between the second and third membrane helix contains the majority of the conserved amino acids of a CDP-alcohol phosphotransferase motif (DGX2 ARX12 GX3 DX3 D). Using point mutagenesis, we provide evidence for a crucial role of this motif in choline binding and enzyme activity. To study the catalytic features of the enzyme, we established a purification protocol for recombinant Pcs. The enzyme forms stable oligomers and exhibits broad substrate specificity towards choline derivatives. The presence of CDP-DAG and manganese is a prerequisite for cooperative binding of choline. PC formation by Pcs is reversible and proceeds via two successive reactions. In a first choline- and manganese-independent reaction, CDP-DAG is hydrolyzed releasing a CMP molecule. The resulting phosphatidyl intermediate reacts with choline in a second manganese-dependent step to form PC.
  Pcs and Pcs bind by molecular sieving (1, 2, 3).
authors.affiliation: Department of Microbial Biology, Ruhr University Bochum, Germany.
authors.forename: Meriyem
authors.initials: M
authors.lastname: Aktas
authors.forename: Stefan
authors.initials: S
authors.lastname: Köster
authors.forename: Sarah
authors.initials: S
authors.lastname: Kizilirmak
authors.forename: Javier C
authors.initials: JC
authors.lastname: Casanova
authors.forename: Heidi
authors.initials: H
authors.lastname: Betz
authors.forename: Christiane
authors.initials: C
authors.lastname: Fritz
authors.forename: Roman
authors.initials: R
authors.lastname: Moser
authors.forename: Özkan
authors.initials: Ö
authors.lastname: Yildiz
authors.forename: Franz
authors.initials: F
authors.lastname: Narberhaus
mesh_terms: D016960:Agrobacterium tumefaciens / Q000201:enzymology*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002331:Carnitine / Q000737:chemistry; D020134:Catalytic Domain; D002794:Choline / Q000737:chemistry; D004926:Escherichia coli; D008969:Molecular Sequence Data; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D013379:Substrate Specificity; D017855:Transferases (Other Substituted Phosphate Groups) / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D017855:Transferases (Other Substituted Phosphate Groups); C483298:CDP-diacylglycerol choline O-phosphatidyltransferase; D002794:Choline; D002331:Carnitine
keywords: Agrobacterium tumefaciens; CDP-alcohol phosphotransferase; phosphatidylcholine; phosphatidylcholine synthase; phospholipids