Sn-2 Position Of Glycerol Backbone Research Articles

Biosynthesis of structured lipids enriched with medium and long-chain triacylglycerols for human milk fat substitute

Human milk fat is rich in medium and long-chain triacylglycerol (MLCT), especially the triacylglycerol with one medium-chain fatty acid and two long-chain fatty acids (MLL type). To obtain human milk fat substitutes having similarity in medium and long-chain triacylglycerol (MLCT) composition to human milk, structured lipids (SLs) enriched with medium-chain fatty acid and high content of 16:0 at sn-2 position of glycerol backbone were synthesized from catfish oil and coconut oil through enzymatic interesterification. The different immobilized lipases and the reaction conditions (substrate ratio, temperature, enzyme load and reaction time) were investigated. Under the optimal conditions, the content of MLCT and MLL reached 62.14% and 39.85%, respectively. Moreover, the relative content of 16:0 at the sn-2 position was 46.14%, and the most abundant TAGs in the final SL were 12:0/16:0/18:1, 12:0/18:1/18:1, 12:0/14:0/18:1, 12:0/12:0/18:1. The novel SLs as human milk fat substitutes enriched with MLCTs was produced and have potential application in infant formulas.

Increased DHA Production in Seed Oil Using a Selective Lysophosphatidic Acid Acyltransferase.

Metabolic engineering of the omega-3 (ω3) long chain polyunsaturated fatty acid biosynthesis pathway has generated fish oil-like levels of pharmaceutically and nutritionally important docosahexaenoic acid (DHA) in plant seeds. However, the majority of DHA has been accumulated at the sn-1 and sn-3 positions of triacylglycerol (TAG) in these engineered seeds, leaving only a minor amount (∼10%) at sn-2 position and indicating a strong discrimination (or, a very poor specificity) for DHA by seed lysophosphatidic acid acyltransferases (LPAATs), which mediate the acylation of sn-2 position of glycerol backbone. In order to increase the level of DHA at sn-2 position of TAG and to increase overall DHA level in seeds, we attempted to discover DHA-preferring LPAATs. Several LPAATs for acylation of the sn-2 position of the TAG glycerol backbone were investigated for substrate preference for DHA. In transiently expressing these LPAATs in Nicotiana benthamiana, a Mortierella alpina LPAAT had the highest substrate specificity for accumulating DHA onto oleoyl-lysophosphatidic acid (oleoyl-LPA), while the plant LPAATs tested showed lower preference for DHA. In a competition assay with a pool of four ω3 acyl-Coenzyme A (CoA) substrates involved in the DHA biosynthesis pathway, LPAATs from both M. alpina and Emiliania huxleyi showed a high preference for DHA-CoA acylation onto oleoyl-LPA. When docosahexaenoyl-LPA was used as the acyl receiver, M. alpina LPAAT also showed a high preference for DHA-CoA. Stable overexpression of M. alpina LPAAT in an Arabidopsis line that expressed the DHA biosynthesis pathway significantly increased both the total DHA levels and the distribution of DHA onto the sn-2 position of seed TAG. LC-MS analysis of the seed TAG species also confirmed that overexpression of M. alpina LPAAT increased di-DHA and tri-DHA TAGs, suggesting that the M. alpina LPAAT could enrich DHA at the TAG sn-2 position, leading to a metabolic engineering of oil seed for channeling DHA into the sn-2 position of TAG and to a higher DHA level.