title: The significance of C16 fatty acids in the sn-2 positions of glycerolipids in the photosynthetic growth of Synechocystis sp. PCC6803.
abstract: 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. Delta1848 and Delta1848 Delta2060 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 Delta1848 Delta2060 cells incorporate 18:0 and 18:1 in the sn-2 positions. The levels of sll1752 transcripts increased in Delta1848 Delta2060 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. Delta1848 Delta2060 cells grew slowly at 30 degrees C at lower cell density, and exhibited more severe damage at 20 degrees C than wild-type cells. Furthermore, Delta1848 Delta2060 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 Delta1848 Delta2060 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.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Kumiko
authors.initials: K
authors.lastname: Okazaki
authors.forename: Norihiro
authors.initials: N
authors.lastname: Sato
authors.forename: Noriko
authors.initials: N
authors.lastname: Tsuji
authors.forename: Mikio
authors.initials: M
authors.lastname: Tsuzuki
authors.forename: Ikuo
authors.initials: I
authors.lastname: Nishida
mesh_terms: D001483:Base Sequence; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D005227:Fatty Acids / Q000378:metabolism*; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D046939:Synechocystis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D013696:Temperature; D015854:Up-Regulation
chemical_list: D017931:DNA Primers; D005227:Fatty Acids; D008055:Lipids; D010940:Plant Proteins; D002734:Chlorophyll; D000077194:Chlorophyll A