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

Galactolipids [monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG)] are the hallmark lipids of photosynthetic membranes. The galactolipid synthases MGD1 and DGD1 catalyze consecutive galactosyltransfer reactions but localize to the inner and outer chloroplast envelopes, respectively, necessitating intermembrane lipid transfer. Here we show that the N-terminal sequence of DGD1 (NDGD1) is required for galactolipid transfer between the envelopes. Different diglycosyllipid synthases (DGD1, DGD2, and Chloroflexus glucosyltransferase) were introduced into the dgd1-1 mutant of Arabidopsis in fusion with N-terminal extensions (NDGD1 and NDGD2) targeting to the outer envelope. Reconstruction of DGDG synthesis in the outer envelope membrane was observed only with diglycosyllipid synthase fusion proteins carrying NDGD1, indicating that NDGD1 enables galactolipid translocation between envelopes. NDGD1 binds to phosphatidic acid (PA) in membranes and mediates PA-dependent membrane fusion in vitro. These findings provide a mechanism for the sorting and selective channeling of lipid precursors between the galactolipid pools of the two envelope membranes.

DGDG and Glycolipids in Plants and Algae.

Photosynthetic organelles in plants and algae are characterized by the high abundance of glycolipids, including the galactolipids mono- and digalactosyldiacylglycerol (MGDG, DGDG) and the sulfolipid sulfoquinovosyldiacylglycerol (SQDG). Glycolipids are crucial to maintain an optimal efficiency of photosynthesis. During phosphate limitation, the amounts of DGDG and SQDG increase in the plastids of plants, and DGDG is exported to extraplastidial membranes to replace phospholipids. Algae often use betaine lipids as surrogate for phospholipids. Glucuronosyldiacylglycerol (GlcADG) is a further glycolipid that accumulates under phosphate deprived conditions. In contrast to plants, a number of eukaryotic algae contain very long chain polyunsaturated fatty acids of 20 or more carbon atoms in their glycolipids. The pathways and genes for galactolipid and sulfolipid synthesis are largely conserved between plants, Chlorophyta, Rhodophyta and algae with complex plastids derived from secondary or tertiary endosymbiosis. However, the relative contribution of the endoplasmic reticulum- and plastid-derived lipid pathways for glycolipid synthesis varies between plants and algae. The genes for glycolipid synthesis encode precursor proteins imported into the photosynthetic organelles. While most eukaryotic algae contain the plant-like galactolipid (MGD1, DGD1) and sulfolipid (SQD1, SQD2) synthases, the red alga Cyanidioschyzon harbors a cyanobacterium-type DGDG synthase (DgdA), and the amoeba Paulinella, derived from a more recent endosymbiosis event, contains cyanobacterium-type enzymes for MGDG and DGDG synthesis (MgdA, MgdE, DgdA).

Treatment of the anastomotic complications in patients with Crohn's disease.

PURPOSE: Postoperative anastomotic complications in patients with Crohn's disease undergoing bowel resections have a detrimental influence on the long-term outcome. The aim of this study was to evaluate whether patients' prognosis is affected by various treatment strategies of anastomotic complications. METHODS: The term anastomosis-related "intraabdominal septic complication" (IASC) was used for anastomotic leaks, intraabdominal abscesses, anastomotic fistula, peritonitis. Only patients with these complications have been included in the study. Outcome parameters were "surgical recurrence" (i.e., need for repeat bowel resections) and "good surgical outcome" (i.e., no death, no surgical recurrence, no stoma, no enterocutaneous fistula). Patients in group 1 were treated by taking the affected anastomosis down and creating an end stoma. The anastomosis has been preserved in patients of group 2. RESULTS: Between 1992 and Aug 2009, IASC occurred after 56 ileocolic resections for ileal disease and after 26 resections for Crohn's colitis. In patients with ileal disease, 5-year surgical recurrence rate was lower (0% vs. 65%, p = 0.0020) and a good surgical outcome was achieved more frequently at 2 years (100% vs. 25%, p = 0.0001) in group 1 than in group 2. There was no significant difference of long-term outcome between groups in patients with Crohn's colitis. CONCLUSION: In patients suffering anastomotic complications after ileocolic resection for ileal Crohn's disease, the prognosis can be significantly improved by taking down the anastomosis and creating an end ileostomy. Anastomosis can be preserved without an outcome impairment in many patients with Crohn's colitis.