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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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Data Analysis Details Information

Title Data analysis (LC-IT-TOF)
Description Peak areas of individual lipid molecules were calculated based on the m/z values of their molecular-related ions or fragment ions. The ions used for calculation of peak areas are as follows: [M+HCOO]− for MGDG and DGDG, [M–H]− for SQDG and PI, [M+NH4–phosphoglycerol]+ for PG, [M+NH4–phosphoethanolamine]+ for PE, and [M+H]+ for PC. Because the lipid species with the same polar head were eluted at almost the same retention time (see Supplemental Figure 5 online), corrections for overlap of isotopic variants in higher mass lipids were applied.

Ionization efficiency is largely influenced by the nature of the polar headgroups. Thus, the ionization efficiency is assumed to be almost identical when molecules have the same polar headgroups. Levels of individual lipid molecules in the wild-type plant and mutant lines were expressed as relative values against the sum of the peak areas of lipid molecules with the same polar headgroups in the wild type.


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