PMC:4301621 / 17873-22529 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/4301621","sourcedb":"PMC","sourceid":"4301621","source_url":"https://www.ncbi.nlm.nih.gov/pmc/4301621","text":"PUFA biosynthetic pathways based on GSMM\nTo further investigate the pathways associated with PUFA biosynthesis and metabolism, genome annotation, literature mining and KEGG database analysis were performed. ARA is a ω-6 PUFA synthesized by M. alpina (Figure 3). ARA (c204(6)) is synthesized from acetyl-CoA in 38 enzymatic steps, including the de novo synthesis of palmitic acid (c160) and the synthesis of very long chain fatty acids. During PUFA biosynthesis, all fatty acids should be in the form of acyl-CoA [2]. Desaturase and elongase were necessary for the conversion of octadecanoyl-CoA (c180coa) to ARA. Δ9 desaturase [28] (MA-055-51, MA-101-533, MA-184-235), Δ12 desaturase [29] (MA-334-414) and Δ6 desaturase [30,31] (MA-268-54, MA-101-36) catalyzed the conversion of c180coa into γ-linolenoyl-CoA (c183(6)coa) which was subsequently lengthened to 8,11,14-eicosatrienoyl-CoA (c203(6)coa) by an elongase such as ELO/GLELO [30] (MA-189-257), MAELO [32] (MA-184-206) or MALCE1 [33] (MA-073-327, MA-320-221). Δ5 desaturase [10] (MA-326-160) catalyzed c203(6)coa to arachidonyl-CoA (c204(6)coa), which was finally hydrolyzed to c204(6) by choloyl-CoA hydrolase (MA-049-4, MA-139-47).\nFigure 3 Synthesis pathway of PUFAs in M . alpina . (accoa: acetyl-CoA, acp: acyl-carrier protein, acacp: Acetyl-[acyl-carrier protein], malcoa: malonyl-CoA, malacp: malonyl-[acp], aacacp: acetoacetyl [acp], c4hacp: (3R)-3-Hydroxybutanoyl-[acp], c4dacp: but-2-enoyl-[acp], c40acp: butanoyl-[acp], c6oacp: 3-oxohexanoyl-[acp], c6hacp: 3-hydroxyhexanoyl-[acp], c6dacp: hex-2-enoyl-[acp], c60acp: hexanoyl-[acp], c8oacp: 3-oxooctanoyl-[acp], c8hacp: 3-hydroxyoctanoyl-[acp], c8dacp: oct-2-enoyl-[acp], c80acp: octanoyl-[acp], c10oacp: 3-oxodecanoyl-[acp], c10hacp: 3-hydroxydecanoyl-[acp], c10dacp: dec-2-enoyl-[acp], c100acp: decanoyl-[acp], c12oacp: 3-oxododecanoyl-[acp], c12hacp: 3-hydroxy-dodecanoyl-[acp], c12dacp: dodec-2-enoyl-[acp], c120acp: dodecanoyl-[acp], c14oacp: 3-oxomyristoyl-[acp], c14dacp: tetradec-2-enoyl-[acp], c14hacp: 3-hydroxymyristoyl-[acp], c140acp: myristoyl-[acp], c16oacp: 3-oxohexadecanoyl-[acp], c16hacp: (3R)-3-Hydroxypalmitoyl-[acp], c16dacp: hexadec-2-enoyl-[acp], c160acp: hexadecanoyl-[acp], c160: palmitic acid, c160coa: hexadecanoyl-CoA, c180coa: octadecanoyl-CoA, c181coa: octadecenoyl-CoA, c182coa: linoleoyl-CoA, c183(6)coa: gamma-Linolenoyl-CoA, c203(6)coa: 8,11,14-Eicosatrienoyl-CoA, c204(6)coa: Arachidonyl-CoA, c204(6): ARA, c183(3)coa: alpha-Linolenoyl-CoA, c184(3)coa: Stearidonoyl-CoA, c204(3)coa: (11Z,14Z,17Z)-Icosatrienoyl-CoA, c205(3)coa: eicosapentaenoyl-CoA, c225(3)coa: (7Z,10Z,13Z,16Z,19Z)-Docosapentaenoyl-CoA, c245(3)coa: (9Z,12Z,15Z,18Z,21Z)-Tetracosaheptaenoyl-CoA, c246(3)coa: (6Z,9Z,12Z,15Z,18Z,21Z)-Tetracosahexaenoyl-CoA, c226(3)coa: (4Z,7Z,10Z,13Z,16Z,19Z)-Docosahexaenoyl-CoA).\nM. alpina is capable of producing ARA and EPA, and EPA can be produced via the ω-3 or the ω-6 PUFA biosynthetic pathways through ARA desaturation [34]. During EPA biosynthesis, Δ15 (ω3) desaturase (MA-072-10) is the key enzyme and was the first fungal desaturase known that uses both 18-carbon and 20-carbon ω-6 PUFAs as substrates [35]. In the ω-3 pathway, (11Z,14Z,17Z)-icosatrienoyl-CoA (c204(3)coa) was used as substrate, while the ω-6 pathway utilized c204(6)coa.\nBoth the maximum and minimum flux of oxygen absorption of DGLA, ARA and EPA production in silico were found to be 1.552, 1.674 and 1.891 mmol gDW−1 h−1 respectively, using FVA. This indicated that the degree of PUFA unsaturation was dependent on oxygen content. Robustness analysis was used to elucidate the effects of oxygen uptake rate on PUFA biosynthesis. The oxygen uptake rate was perturbed by constraints-based flux analysis between 0 and 20 mmol gDW−1 h−1. The minimum growth rate was set at 0.03 h−1, with ARA exchange reaction as the objective function. When oxygen absorption was lower than 2.0 mmol gDW−1 h−1, ARA production increased with oxygen absorption rate (Additional file 5a). However, beyond this range, ARA production gradually declined with increasing oxygen uptake rate. As reported by Higashiyama et al., when the DO concentration range was 10-15 ppm, the ARA yield was enhanced 1.6-fold over a DO of 7 ppm, and a DO between 20 and 50 ppm drastically decreased ARA production [36]. This indicated that excessive oxygen exposure during fermentation could impair ARA overproduction. During ARA biosynthesis, high oxygen concentrations may affect metabolism and cell growth in the filamentous mycelia, and beta-oxidation of fatty acids may be needed to obtain the extra energy required for adaptation to the high oxygen conditions.","divisions":[{"label":"title","span":{"begin":0,"end":40}},{"label":"p","span":{"begin":41,"end":2833}},{"label":"figure","span":{"begin":1190,"end":2833}},{"label":"label","span":{"begin":1190,"end":1198}},{"label":"caption","span":{"begin":1199,"end":2833}},{"label":"p","span":{"begin":1199,"end":2833}},{"label":"p","span":{"begin":2834,"end":3302}}],"tracks":[{"project":"2_test","denotations":[{"id":"25582171-22174787-14905487","span":{"begin":513,"end":514},"obj":"22174787"},{"id":"25582171-16133334-14905488","span":{"begin":628,"end":630},"obj":"16133334"},{"id":"25582171-19217543-14905489","span":{"begin":685,"end":687},"obj":"19217543"},{"id":"25582171-12784608-14905490","span":{"begin":724,"end":726},"obj":"12784608"},{"id":"25582171-18795285-14905491","span":{"begin":958,"end":960},"obj":"18795285"},{"id":"25582171-19415268-14905492","span":{"begin":986,"end":988},"obj":"19415268"},{"id":"25582171-16233793-14905493","span":{"begin":1031,"end":1033},"obj":"16233793"},{"id":"25582171-1818539-14905494","span":{"begin":2981,"end":2983},"obj":"1818539"},{"id":"25582171-15538555-14905495","span":{"begin":3167,"end":3169},"obj":"15538555"},{"id":"25582171-10099624-14905496","span":{"begin":4305,"end":4307},"obj":"10099624"}],"attributes":[{"subj":"25582171-22174787-14905487","pred":"source","obj":"2_test"},{"subj":"25582171-16133334-14905488","pred":"source","obj":"2_test"},{"subj":"25582171-19217543-14905489","pred":"source","obj":"2_test"},{"subj":"25582171-12784608-14905490","pred":"source","obj":"2_test"},{"subj":"25582171-18795285-14905491","pred":"source","obj":"2_test"},{"subj":"25582171-19415268-14905492","pred":"source","obj":"2_test"},{"subj":"25582171-16233793-14905493","pred":"source","obj":"2_test"},{"subj":"25582171-1818539-14905494","pred":"source","obj":"2_test"},{"subj":"25582171-15538555-14905495","pred":"source","obj":"2_test"},{"subj":"25582171-10099624-14905496","pred":"source","obj":"2_test"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"2_test","color":"#93deec","default":true}]}]}}