Oxygenic photosynthesis without galactolipids
Glycolipid biosynthetic pathway elucidated 30 years after suggestion
Graduate School of Arts and Sciences / College of Arts and Sciences
Professor Naoki Sato at the University of Tokyo, in collaboration with Associate Professor Koichiro Awai at Shizuoka University and Professor Hiroyuki Ohta at the Tokyo Institute of Technology, has identified the complete pathway of glycolipid biosynthesis in cyanobacteria, and at the same time, demonstrated that galactolipids, which are always present in photosynthetic organisms, are not necessary for photosynthesis.
Cyanobacteria are prokaryotes (single-celled organisms that lack membrane-bound organelles such as a nucleus) that perform oxygenic photosynthesis (a type of photosynthesis that produces oxygen), and are believed to be the origin of the chloroplasts found inside the cells of plants and algae. The initial reactions in the process of photosynthesis occur in the photosynthetic membranes that consist of galactolipids (containing one or two galactose moieties), which is therefore believed to be necessary for photosynthesis. Further, cyanobacteria synthesize glycolipids in the process of converting glucolipids to galactolipids.
In this research the group identified the gene mgdE that encodes the enzyme that converts glucolipid to galactolipid. By disrupting this gene, the group demonstrated that oxygenic photosynthesis is possible with a photosynthetic membrane consisting only of glucolipids, overturning the current understanding of the photosynthetic process. Professor Sato proposed the route for glycolipid synthesis in his doctoral thesis 30 years ago. With this discovery, the genes for all the enzymes in the route for glycolipid synthesis, first proposed by Professor Sato in his doctoral thesis 30 years ago, have been identified.
K. Awai, H. Ohta and N. Sato,
“Oxygenic photosynthesis without galactolipids”,
Proceedings of the National Academy of Sciences Online Edition: 2014/9/2 (Japan time), doi: 10.1073/pnas.1403708111.