Digalactosyldiacylglycerol Is Required for Stabilization of the Oxygen-Evolving Complex in Photosystem II

Abstract

The galactolipid digalactosyldiacylglycerol (DGDG) is present in the thylakoid membranes of oxygenic photosynthetic organisms such as higher plants and cyanobacteria. Recent x-ray crystallographic analysis of protein-cofactor supercomplexes in thylakoid membranes revealed that DGDG molecules are present in the photosystem II (PSII) complex (four molecules per monomer), suggesting that DGDG molecules play important roles in folding and assembly of subunits in the PSII complex. However, the specific role of DGDG in PSII has not been fully clarified. In this study, we identified the dgdA gene (slr1508, a ycf82 homolog) of Synechocystis sp. PCC6803 that presumably encodes a DGDG synthase involved in the biosynthesis of DGDG by comparison of genomic sequence data. Disruption of the dgdA gene resulted in a mutant defective in DGDG synthesis. Despite the lack of DGDG, the mutant cells grew as rapidly as the wild-type cells, indicating that DGDG is not essential for growth in Synechocystis. However, we found that oxygen-evolving activity of PSII was significantly decreased in the mutant. Analyses of the PSII complex purified from the mutant cells indicated that the extrinsic proteins PsbU, PsbV, and PsbO, which stabilize the oxygen-evolving complex, were substantially dissociated from the PSII complex. In addition, we found that heat susceptibility but not dark-induced inactivation of oxygen-evolving activity was notably increased in the mutant cells in comparison to the wild-type cells, suggesting that the PsbU subunit is dissociated from the PSII complex even in vivo. These results demonstrate that DGDG plays important roles in PSII through the binding of extrinsic proteins required for stabilization of the oxygen-evolving complex.

Mono- and digalactosyldiacylglycerol composition of dinoflagellates. IV. Temperature-induced modulation of fatty acid regiochemistry as observed by electrospray ionization/mass spectrometry

“…C, but will not grow much beyond 25 C; our unpublished results reveal the upper temperature limit for these strains to be approximately 28 C. The temperature-dependent modification of DGDG across these species of Pyrocystis is consistent with the response found in the cyanobacterium Synechocystis (Sakurai et al 2007 and references reviewed therein). The fact that the more unsaturated 20:5/18:5 form of DGDG is generally more abundant at the lowest temperature, and that the converse is true for the 20:5/18:4 DGDG fits with our general understanding of lipid/fatty acid responses to temperature.…”

Synthesis and transfer of galactolipids in the chloroplast envelope membranes of Arabidopsis thaliana

“…S1 and S2). The Cyanidiales (Rhodophyta) harbor DGDG synthases distinct from those in plants; the Cyanidiales sequences are related to cyanobacterial DgdA (17,18). Database searches with PSI BLAST using NDGD1 from Arabidopsis resulted in the retrieval of NDGD1 sequences in all Streptophyta, including Klebsormidium, but not in other organisms.…”

“…S1), and NDGD1 sequences occur in Streptophyta (SI Appendix, Fig. S1) (16)(17)(18). Cyanobacteria are surrounded by two envelope membranes, the presumed progenitors for the iEM and the oEM of the chloroplast (37).…”

Knocking Down of Isoprene Emission Modifies the Lipid Matrix of Thylakoid Membranes and Influences the Chloroplast Ultrastructure in Poplar

“…They exert structural functions and improve the thermal stability of membranes, particularly at high temperatures (Krumova et al, 2010). DGDGs bind to PSII (Loll et al, 2007) through the formation of hydrogen bonds with Tyr in PSII (Gabashvili et al, 1998), and DGDGs are also important for binding of extrinsic proteins required for the stabilization of the oxygen-evolving complex (Sakurai et al, 2007). Our data clearly indicate that the suppression of isoprene biosynthesis significantly diminished the level of DGDGs in poplar chloroplasts, which was accompanied by a reduction of the RCI and RCII concentrations (Fig.…”