title: Arabidopsis cytosolic acyl-CoA-binding proteins ACBP4, ACBP5 and ACBP6 have overlapping but distinct roles in seed development.
abstract: Eukaryotic cytosolic ACBPs (acyl-CoA-binding proteins) bind acyl-CoA esters and maintain a cytosolic acyl-CoA pool, but the thermodynamics of their protein-lipid interactions and physiological relevance in plants are not well understood. Arabidopsis has three cytosolic ACBPs which have been identified as AtACBP4, AtACBP5 and AtACBP6, and microarray data indicated that all of them are expressed in seeds; AtACBP4 is expressed in early embryogenesis, whereas AtACBP5 is expressed later. ITC (isothermal titration calorimetry) in combination with transgenic Arabidopsis lines were used to investigate the roles of these three ACBPs from Arabidopsis thaliana. The dissociation constants, stoichiometry and enthalpy change of AtACBP interactions with various acyl-CoA esters were determined using ITC. Strong binding of recombinant (r) AtACBP6 with long-chain acyl-CoA (C16- to C18-CoA) esters was observed with dissociation constants in the nanomolar range. However, the affinity of rAtACBP4 and rAtACBP5 to these acyl-CoA esters was much weaker (dissociation constants in the micromolar range), suggesting that they interact with acyl-CoA esters differently from rAtACBP6. When transgenic Arabidopsis expressing AtACBP6pro::GUS was generated, strong GUS (β-glucuronidase) expression in cotyledonary-staged embryos and seedlings prompted us to measure the acyl-CoA contents of the acbp6 mutant. This mutant accumulated higher levels of C18:1-CoA and C18:1- and C18:2-CoAs in cotyledonary-staged embryos and seedlings, respectively, in comparison with the wild type. The acbp4acbp5acbp6 mutant showed the lightest seed weight and highest sensitivity to abscisic acid during germination, suggesting their physiological functions in seeds.
authors.affiliation: *School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China.
authors.forename: An-Shan
authors.initials: AS
authors.lastname: Hsiao
authors.affiliation: †Department of Biological Chemistry, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, U.K.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Haslam
authors.affiliation: †Department of Biological Chemistry, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, U.K.
authors.forename: Louise V
authors.initials: LV
authors.lastname: Michaelson
authors.affiliation: *School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China.
authors.forename: Pan
authors.initials: P
authors.lastname: Liao
authors.affiliation: *School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China.
authors.forename: Qin-Fang
authors.initials: QF
authors.lastname: Chen
authors.affiliation: ‡Department of Cell and Molecular Biology, Uppsala University, Box 596, Biomedical Center, 751 24 Uppsala, Sweden.
authors.forename: Sanjeewani
authors.initials: S
authors.lastname: Sooriyaarachchi
authors.affiliation: §Science for Life Laboratory, Uppsala University, Box 596, Biomedical Center, 751 24 Uppsala, Sweden.
authors.forename: Sherry L
authors.initials: SL
authors.lastname: Mowbray
authors.affiliation: †Department of Biological Chemistry, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, U.K.
authors.forename: Johnathan A
authors.initials: JA
authors.lastname: Napier
authors.affiliation: ║Department of Biochemistry, The University of Hong Kong, Pokfulam, Hong Kong, China.
authors.forename: Julian A
authors.initials: JA
authors.lastname: Tanner
authors.affiliation: *School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China.
authors.forename: Mee-Len
authors.initials: ML
authors.lastname: Chye
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D000214:Acyl Coenzyme A / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001667:Binding, Competitive; D002151:Calorimetry / Q000379:methods; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D004952:Esters / Q000378:metabolism; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D018525:Germination / Q000187:drug effects / Q000235:genetics; D009154:Mutation; D010937:Plant Growth Regulators / Q000494:pharmacology; D030821:Plants, Genetically Modified; D011485:Protein Binding; D012639:Seeds / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D013816:Thermodynamics
chemical_list: C495420:ACBP4 protein, Arabidopsis; C495421:ACBP5 protein, Arabidopsis; C532782:ACBP6 protein, Arabidopsis; D000214:Acyl Coenzyme A; D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D004952:Esters; D010937:Plant Growth Regulators; D000040:Abscisic Acid