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Sample Set Information

ID TSE1304
Title A chloroplastic UDP-glucose pyrophosphorylase from Arabidopsis is the committed enzyme for the first step of sulfolipid biosynthesis.
Description Plants synthesize a sulfur-containing lipid, sulfoquinovosyldiacylglycerol, which is one of three nonphosphorus glycerolipids that provide the bulk of the structural lipids in photosynthetic membranes. Here, the identification of a novel gene, UDP-glucose pyrophosphorylase3 (UGP3), required for sulfolipid biosynthesis is described. Transcriptome coexpression analysis demonstrated highly correlated expression of UGP3 with known genes for sulfolipid biosynthesis in Arabidopsis thaliana. Liquid chromatography-mass spectrometry analysis of leaf lipids in two Arabidopsis ugp3 mutants revealed that no sulfolipid was accumulated in these mutants, indicating the participation of UGP3 in sulfolipid biosynthesis. From the deduced amino acid sequence, UGP3 was presumed to be a UDP-glucose pyrophosphorylase (UGPase) involved in the generation of UDP-glucose, serving as the precursor of the polar head of sulfolipid. Recombinant UGP3 was able to catalyze the formation of UDP-glucose from glucose-1-phosphate and UTP. A transient assay using fluorescence fusion proteins and UGPase activity in isolated chloroplasts indicated chloroplastic localization of UGP3. The transcription level of UGP3 was increased by phosphate starvation. A comparative genomics study on UGP3 homologs across different plant species suggested the structural and functional conservation of the proteins and, thus, a committing role for UGP3 in sulfolipid synthesis.
Authors Okazaki Y, Shimojima M, Sawada Y, Toyooka K, Narisawa T, Mochida K, Tanaka H, Matsuda F, Hirai A, Hirai MY, Ohta H, Saito K.
Reference Plant Cell. 2009 Mar;21(3):892-909. doi: 10.1105/tpc.108.063925. Epub 2009 Mar 13.

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Analytical Method Details Information

Title LC-MS Analysis of Lipid Extracts
Instrument LC, Shimadzu LC-20AD system; MS, Shimadzu LCMS-IT-TOF
Instrument Type
Ionization ESI
Ion Mode positive and negative
Description Total lipids were extracted according to the method of Bligh and Dyer (1959). Crude lipid extracts were dissolved in chloroform and subjected to LC-MS analysis using a Shimadzu LCMS-IT-TOF mass spectrometer combined with a Shimadzu LC-20AD HPLC system. A two-solvent system was used to generate the mobile phase: solvent A, methanol-water (95:5, v/v) containing 0.2% ammonium formate, pH 5.9; solvent B, acetonitrile-methanol-water (95:2:3, v/v/v) containing 0.2% ammonium formate, pH 5.9. The pH of both solvents A and B was adjusted by adding 30% NH4OH to the mixtures of solvents containing 0.2% (v/v) formic acid. At the beginning of the gradient, the mobile phase was 100% solvent B for 3.33 min. Solvent B was linearly decreased to 60% over 6.67 min and successively decreased to 30% over 1.33 min. Solvent B was held at 30% for 3.33 min and then increased to 100% for reequilibration. The flow rate was held 0.18 mL min−1 for 3.33 min at the beginning of the gradient and linearly increased to 0.2 mL min−1 over 11.33 min. The flow rate was then increased to 0.4 mL min−1 at 14.66 min after the beginning of the gradient, maintained for 13.33 min, and then decreased to 0.18 mL min−1. Total elution time was 40 min.

High-resolution ESI-MS were acquired in both positive and negative ion modes by switching the polarity during individual analyses. Conditions for measurement of ESI-MS were as follows: mass range, m/z 150 to 1600; interface voltage, 4.5 V; curved desolvation line temperature, 200°C; heat block temperature, 200°C; ion accumulation time, 10 ms; detector voltage, 1.80 kV; nebulizer gas, N2 (15 L·min−1). The collision-induced dissociation experiment was performed using Ar as the collision gas, with a relative collision energy of 50% and a relative collision gas flow of 50%.


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