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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

The Significance of C16 Fatty Acids in the sn-2 Positions of Glycerolipids in the Photosynthetic Growth of Synechocystis sp. PCC6803^1,[W]

Department of Biological Sciences, Graduate School of Science, University of Tokyo, Bunkyou-ku, Tokyo 113–0033, Japan (K.O.); School of Life Science, Tokyo University of Pharmacy and Life Science, Hachioji, Tokyo 192–0392, Japan (N.S., N.T., M.T.); and Department of Biochemistry and Molecular Biology, Faculty of Science, Saitama University, Sakura-Ku, Saitama-Shi, Saitama 338–8570, Japan (I.N.)

Most extant cyanobacteria contain C16 fatty acids in the sn-2 positions of glycerolipids, which are regulated by lysophosphatidic acid acyltransferase (LPAAT; EC 2.3.1.51). Synechocystis sp. PCC6803 contains sll1848, sll1752, and slr2060 as putative acyltransferase genes. sll1848 was recently reported to encode an indispensable palmitoyl-specific LPAAT; however, here we show that each of the three genes is dispensable. 1848 and 1848 2060 cells had markedly higher contents of stearate (18:0), oleate (18:1), and linoleate (18:2) in place of palmitate (16:0) in the sn-2 positions, suggesting that 1848 2060 cells incorporate 18:0 and 18:1 in the sn-2 positions. The levels of sll1752 transcripts increased in 1848 2060 cells. This was accompanied by increased LPAAT activity toward 18:0 coenzyme A and its derivative in the membrane fraction. From these findings, together with the activity of a recombinant sll1752 protein and complementation of the Escherichia coli LPAAT mutant plsC, we conclude that sll1752 encodes a second LPAAT that prefers stearoyl and oleoyl substrates. 1848 2060 cells grew slowly at 30°C at lower cell density, and exhibited more severe damage at 20°C than wild-type cells. Furthermore, 1848 2060 cells exhibited photoinhibition more severely than wild-type cells. A phycobilisome core-membrane linker protein (slr0335) was also found to be susceptible to protein extraction under our conditions; its content decreased in the membrane fractions of 1848 2060 cells. We conclude that C16 fatty acids in sn-2 positions are preferred in the photosynthetic growth of this cyanobacterium, despite sll1752 orthologs being conserved in most cyanobacteria. However, no sll1752 ortholog is conserved among photosynthetic eukaryotes including Cyanidioschyzon merolae.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Ikuo Nishida (nishida{at}molbiol.saitama-u.ac.jp).

^[W] The online version of this article contains Web-only data.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.075796.

^* Corresponding author; nishida{at}molbiol.saitama-u.ac.jp; fax 81–48–858–3384.

Received December 26, 2005; returned for revision March 27, 2006; accepted April 4, 2006.

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