title: Characterization of phosphatidylinositol phosphate kinases from the moss Physcomitrella patens: PpPIPK1 and PpPIPK2.
abstract: Phosphoinositides (PIs) play a major role in eukaryotic cells, despite being a minor component of most membranes. This is the first report on PI metabolism in a bryophyte, the moss Physcomitrella patens. Moss PI composition is similar to that of other land plants growing under normal conditions. In contrast to the large number of PIPK genes present in flowering plants, the P. patens genome encodes only two type I/II PIPK genes, PpPIPK1 and PpPIPK2, which are very similar at both the nucleotide and protein product levels. However, the expression of the two genes is differentially regulated, and in vitro biochemical characterization shows that the resulting enzymes have different substrate specificities. PpPIPK1 uses PtdIns4P and PtdIns3P with similar preference and also metabolizes PtdIns(3,4)P(2) to produce PtdIns(3,4,5)P(3), a PI not yet detected in intact plant cells. PpPIPK2 prefers PtdIns as substrate and is much less active towards PtdIns4P and PtdIns3P. Thus, PpPIPK2 shows properties reminiscent of both PtdInsP-kinase and PtdIns-kinases. Moreover, a substitution of glutamic acid by alanine in the activation loop drastically reduced PpPIPK1 activity and altered the substrate specificity to PtdIns5P being the preferred substrate compared with PtdIns4P and PtdIns3P. These findings demonstrate that the substrate specificity of plant PIPKs is determined in a plant-specific manner, which provides new insights into the regulatory modes of PIPK activity in plants.
authors.affiliation: Department of Biochemistry, Center for Chemistry and Chemical Engineering, Lund University, PO Box 124, SE-22100 Lund, Sweden.
authors.forename: Laura
authors.initials: L
authors.lastname: Saavedra
authors.forename: Virginia
authors.initials: V
authors.lastname: Balbi
authors.forename: Stephen K
authors.initials: SK
authors.lastname: Dove
authors.forename: Yuji
authors.initials: Y
authors.lastname: Hiwatashi
authors.forename: Koji
authors.initials: K
authors.lastname: Mikami
authors.forename: Marianne
authors.initials: M
authors.lastname: Sommarin
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D019068:Bryopsida / Q000201:enzymology* / Q000235:genetics; D002462:Cell Membrane / Q000201:enzymology; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D008969:Molecular Sequence Data; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D018749:RNA, Plant / Q000235:genetics; D016415:Sequence Alignment; D013379:Substrate Specificity
chemical_list: D018129:Phosphatidylinositol Phosphates; D018749:RNA, Plant; C055525:phosphatidylinositol 3-phosphate; C037178:phosphatidylinositol 4-phosphate; D017853:Phosphotransferases (Alcohol Group Acceptor)