Regulation of TG accumulation and lipid droplet morphology by the novel TLDP1 in Aurantiochytrium limacinum F26-b

Abstract

Thraustochytrids are marine single-cell protists that produce large amounts of PUFAs, such as DHA. They accumulate PUFAs in lipid droplets (LDs), mainly as constituent(s) of triacylglycerol (TG). We identified a novel protein in the LD fraction of F26-b using 2D-difference gel electrophoresis. The protein clustered with orthologs of thraustochytrids; however, the cluster was evolutionally different from known PAT family proteins or plant LD protein; thus, we named it thraustochytrid-specific LD protein 1 (TLDP1). TLDP1 surrounded LDs when expressed as a GFP-tagged form. Disruption of the gene decreased the content of TG and number of LDs per cell; however, irregular and unusually large LDs were generated in -deficient mutants. Although the level of TG synthesis was unchanged by the disruption of, the level of TG degradation was higher in -deficient mutants than in the WT. These phenotypic abnormalities in-deficient mutants were restored by the expression of These results indicate that TLDP1 is a thraustochytrid-specific LD protein and regulates the TG accumulation and LD morphology in F26-b.

The lipid metabolism in thraustochytrids

“…Less direct but promising approaches were also undertaken. For example, it was shown that disrupting a thraustochytrid-specific lipid droplet protein impacts TAG accumulation in A. limacinum [138]. Because of their high number of double bonds, PUFAs are highly sensitive to reactive oxygen species, which presumably increase their rate of degradation.…”

The Nutritional and Pharmacological Potential of New Australian Thraustochytrids Isolated from Mangrove Sediments

“…This suggests proteins exist in suspension after the aqueous extraction procedure and cover the OBs [44]. The protein-coated fatty-acid-rich OBs were discovered in various plant and microalgal cells, and their characteristics were extensively studied due to their technological importance for the food industry [45,46]. The isoelectric point of OBs from thraustochytrids was lower than that observed in plant species (between 4 and 6) [44,47].…”

The glycerol-3-phosphate acyltransferase PLAT2 functions in the generation of DHA-rich glycerolipids in Aurantiochytrium limacinum F26-b

“…DG, PC, and TG were analyzed by LC-ESI MS according to the method described by Ikeda et al [34]. LC-ESI MS was performed using a HPLC system (Agilent Technologies) coupled to a MS apparatus (3200 QTRAP; AB Sciex) [20]. A binary solvent gradient with a flow rate of 200 μl/min was used to separate DG, PC, and TG by reverse-phase chromatography using InerSustain C18 (2.1 x 150 mm, 5 μm; GL Sciences).…”

“…Recently, it was reported that Aurantiochytrium and related genus have several (but not all) genes involved in elongase/desaturase pathway; however, the biological significance of these genes remains unknown [16, 17]. De novo synthesized DHA is incorporated to glycerolipids, such as triacylglycerol (TG) and phosphatidylcholine (PC), as an ester-linked acyl chain(s), and then accumulated in LDs and cell membranes [18–20].…”

“…A . limacinum used in this study possesses DHA-rich TG and PC such as TG 60:12 (22:6/22:6/16:0, two DHAs/molecule), TG 66:18 (22:6/22:6/22:6, three DHAs/molecule), and PC 44:12 (22:6/22:6, two DHAs/molecule) [20]. These DHA-rich glycerolipids are characteristic to thraustochytrids, but not other marine microorganisms belonging to Stramenopiles such as diatoms.…”