Journal Article

Is Monoglucosyldiacylglycerol a Precursor to Monogalactosyldiacylglycerol in All Cyanobacteria?

Naoki Sato

in Plant and Cell Physiology

Volume 56, issue 10, pages 1890-1899
Published in print October 2015 | ISSN: 0032-0781
Published online August 2015 | e-ISSN: 1471-9053 | DOI: https://dx.doi.org/10.1093/pcp/pcv116
Is Monoglucosyldiacylglycerol a Precursor to Monogalactosyldiacylglycerol in All Cyanobacteria?

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Monogalactosyldiacylglycerol (MGDG) is ubiquitous in the photosynthetic membranes of cyanobacteria and chloroplasts. It is synthesized by galactosylation of diacylglycerol (DAG) in the chloroplasts, whereas it is produced by epimerization of monoglucosyldiacylglycerol (GlcDG) in at least several cyanobacteria that have been analyzed such as Synechocystis sp. PCC 6803. A previous study, however, showed that the mgdE gene encoding the epimerase is absent in some cyanobacteria such as Gloeobacter violaceus, Thermosynechococcus elongatus and Acaryochloris marina. In addition, the N-terminal ‘fatty acid hydroxylase’ domain is lacking in the MgdE protein of Prochlorococcus marinus. These problems may cast doubt upon the general (or exclusive) role of MgdE in the epimerization of GlcDG to MGDG in cyanobacteria. In addition, GlcDG is usually present at a very low level, and the structural determination of endogenous GlcDG has not been accomplished with cyanobacterial samples. In this study, I determined the structure of GlcDG from Anabaena variabilis by 1H- and 13C-nuclear magnetic resonance (NMR) spectroscopy. I then showed that G. violaceus, T. elongatus, A. marina and P. marinus contain GlcDG. In all cases, GlcDG consisted of fewer unsaturated molecular species than MGDG, providing further evidence that GlcDG is a precursor to MGDG. The conversion of GlcDG to MGDG was also demonstrated by radiolabeling and chase experiments in G. violaceus and P. marinus. These results demonstrate that all the analyzed cyanobacteria contain GlcDG, which is converted to MGDG, and suggest that an alternative epimerase is required for MGDG synthesis in these cyanobacteria.

Keywords: Cyanobacteria; Lipid metabolism; Mass spectrometry; Monoglucosyldiacylglycerol; NMR spectroscopy

Journal Article.  5130 words.  Illustrated.

Subjects: Molecular Biology and Genetics ; Biotechnology ; Biochemistry ; Bioinformatics and Computational Biology ; Molecular and Cell Biology ; Plant Sciences and Forestry ; Plant Physiology

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