Triacylglycerols are the predominant storage form of energy in eukaryotes. As obesity has become a worldwide problem and excessive accumulation of triacylglycerols in adipose tissue causes obesity, enzymes catalyzing the synthesis of triacylglycerols are of great interest. Acyl CoA:diacylglycerol acyltransferase (DGAT), including the isoforms DGAT1 and DGAT2, catalyze the final and committed step in triacylglycerol synthesis. Proteins that physically interact with DGAT1 may provide information regarding the metabolic role of DGAT1. We chose HEK-293T cell line to express DGAT1 and used mass spectrometry to identify proteins that co-immunoprecipitated with DGAT1. We confirmed that DGAT2 and ACAT1 did interact with DGAT1. The interaction of DGAT1 with DGAT2 appeared to interrupt the synthesis of triacylglycerol since the co-expression of DGAT1 and DGAT2 was expected to increase triacylglycerol synthesis. This implied that DGAT1 and DGAT2 might serve different functional roles. On the other hand, DGAT1 overexpression may increase the synthesis of cholesterol esters that was the product of ACAT1. Additionally, ACAT1 overexpression did increase triacylglycerol synthesis and ACAT1 disruption by siRNA did decrease triacylglycerol synthesis. Our findings indicated that DGAT1 and ACAT1 might be involved in the same lipid-synthesizing protein complex.

The term "lipid" covers an extremely diverse range of chemical or molecular species. Lipids, defined as molecules that are sparingly soluble in water but readily soluble in organic solvents, are broadly categorized into "neutral " or "apolar" lipids, and "amphiphilic” or "polar" lipids. Neutral lipids will include simple hydrocarbons, carotenes, triacylglycerols, wax esters, sterol eaters, as wel1 as other lipids such as fatty acids, polyprenols, and sterols In which the hydrophilic function has little Impact on the overall molecular characteristics. Polar lipids include phospholipids, glycolipids, sulfolipids, some sphingolipids, oxygenated carotenoids and chlorophylls.

Transcriptome analysis based on deep expressed sequence tag (EST) sequencing allows quantitative comparisons of gene expression across multiple species. Using pyrosequencing, we generated over 7 million ESTs from four stages of developing seeds of Ricinus communis, Brassica napus, Euonymus alatus and Tropaeolum majus, which differ in their storage tissue for oil, their ability to photosynthesize and in the structure and content of their triacylglycerols (TAG). The larger number of ESTs in these 16 datasets provided reliable estimates of the expression of acyltransferases and other enzymes expressed at low levels. Analysis of EST levels from these oilseeds revealed both conserved and distinct species-specific expression patterns for genes involved in the synthesis of glycerolipids and their precursors. Independent of the species and tissue type, ESTs for core fatty acid synthesis enzymes maintained a conserved stoichiometry and a strong correlation in temporal profiles throughout seed development. However, ESTs associated with non-plastid enzymes of oil biosynthesis displayed dissimilar temporal patterns indicative of different regulation. The EST levels for several genes potentially involved in accumulation of unusual TAG structures were distinct. Comparison of expression of members from multi-gene families allowed the identification of specific isoforms with conserved function in oil biosynthesis. In all four oilseeds, ESTs for Rubisco were present, suggesting its possible role in carbon metabolism, irrespective of light availability. Together, these data provide a resource for use in comparative and functional genomics of diverse oilseeds. Expression data for more than 350 genes encoding enzymes and proteins involved in lipid metabolism are available at the 'ARALIP' website ().