Engineering yeast for tailored fatty acid profiles

Abstract

The demand for sustainable and eco-friendly alternatives to fossil and plant oil-derived chemicals has spurred interest in microbial production of lipids, particularly triacylglycerols, fatty acids, and their derivatives. Yeasts are promising platforms for synthesizing these compounds due to their high lipid accumulation capabilities, robust growth, and generally recognized as safe (GRAS) status. There is vast interest in fatty acid and triacylglycerol products with tailored fatty acid chain lengths and compositions, such as polyunsaturated fatty acids and substitutes for cocoa butter and palm oil. However, microbes naturally produce a limited set of mostly long-chain fatty acids, necessitating the development of microbial cell factories with customized fatty acid profiles. This review explores the capabilities of key enzymes involved in fatty acid and triacylglycerol synthesis, including fatty acid synthases, desaturases, elongases, and acyltransferases. It discusses factors influencing fatty acid composition and presents engineering strategies to enhance fatty acid synthesis. Specifically, we highlight successful engineering approaches to modify fatty acid profiles in triacylglycerols and produce tailored fatty acids, and we offer recommendations for host selection to streamline engineering efforts. KEY POINTS: • Detailed overview on all basic aspects of fatty acid metabolism in yeast • Comprehensive description of fatty acid profile tailoring in yeast • Extensive summary of applying tailored fatty acid profiles in production processes.

Keywords: Cell factory; Fatty acid; Lipid; Metabolic engineering; Renewable resources; Yeast.

Fig. 1

Metabolic pathways for the synthesis of free fatty acids, fatty acid derivatives, and triacylglycerols. Reactions that influence the FA profile of acyl-CoAs (blue), free fatty acids and derivatives (orange), and triacylglycerols and phospholipids (green) are labeled. Multiple reaction steps are denoted by dashed lines. Enzyme/gene abbreviations and precursor pathways are marked in bold. The turnover of acyl groups from acylated proteins and sphingolipids is not shown. Desaturases, elongases, acyltransferases, and lipases are ER or lipid body-associated (enzyme localization is not visualized for these enzymes). PPP, pentose phosphate pathway; PDH, pyruvate dehydrogenase; ACS, acetyl-CoA synthase; ACL, ATP-citrate lyase; ACC, acetyl-CoA carboxylase; FASI fatty acid synthase type I; FASII, fatty acid synthase type II; TE, thioesterase; mFAS, mammalian fatty acid synthase; FASI-TE, fatty acid synthase type I with integrated thioesterase; FAD, fatty acid desaturases; ELO, fatty acid elongases (and auxiliary enzymes); ASAT, Acyl-CoA:sterol acyltransferase; FAA, acyl-CoA synthetase; DE, derivatizing enzymes; SEH, sterol ester hydrolase; TGL, triacylglycerol lipases; PL, phospholipid lipases; GPAT, glycerol- 3-phosphate acyltransferase; LPAAT, lysophosphatidic acid acyltransferase; PAP, phosphatidic acid phosphatase; DGAT, diacylglycerol acyltransferase; CDS, CDP-diglyceride synthetase; PDAT, phospholipid:diacylglycerol acyltransferase

Fig. 2

Value-added products derived from fatty acids and derivatives, which can be synthesized by yeast cell factories with tuned fatty acid profiles. The simplified metabolic pathway for fatty acid synthesis and major terminal enzymes are depicted. ACC, Acetyl-CoA carboxylase; FAS, fatty acid synthase; TE, thioesterase; WS, wax ester synthase; FAR, fatty acid reductase; CAR, carboxylic acid reductase; ADH, alcohol dehydrogenase; ADO, aldehyde deformylating oxidase; DC, decarboxylase; D, desaturase; E, elongase; AT acyltransferase; FAOH, fatty alcohols