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Open Biol
2025 Jan 01;151:240170. doi: 10.1098/rsob.240170.
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Enzymes enabling the biosynthesis of various C20 polyunsaturated fatty acids in a sea urchin Hemicentrotus pulcherrimus.
Peng Y
,
Haga Y
,
Kabeya N
.
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Sea urchins, integral to marine ecosystems and valued as a delicacy in Asia and Europe, contain physiologically important long-chain (>C20) polyunsaturated fatty acids (PUFA) in their gonads, including arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3) and unusual non-methylene-interrupted fatty acids (NMI-FA) such as 20:2Δ5,11. Although these fatty acids may partially be derived from their diet, such as macroalgae, the present study on Hemicentrotus pulcherrimus has uncovered multiple genes encoding enzymes involved in long-chain PUFA biosynthesis. Specifically, 3 fatty acid desaturases (FadsA, FadsC1 and FadsC2) and 13 elongation of very-long-chain fatty acids proteins (Elovl-like, Elovl1/7-like, Elovl2/5-like, Elovl4-like, Elovl8-like and Elovl6-like A-H) were identified in their genome and transcriptomes. Functional analysis showed that FadsA and FadsC2 function as a Δ5 desaturase and a Δ8 desaturase, respectively, enabling the conversion of 18:2n-6 and 18:3n-3 into ARA and EPA, respectively, along with Elovl, particularly Elovl6-like C. Elovl6-like C demonstrates elongase activity towards both C18 PUFA and monounsaturated fatty acids. Consequently, FadsA and Elovl6-like C enable the synthesis of several NMI-FA, including 20:2Δ5,11 and 20:3Δ5,11,14, from C18 precursors. This indicates that H. pulcherrimus can endogenously synthesize a wide variety of C20 PUFA and NMI-FA, highlighting active biosynthesis pathways within sea urchins.
Figure 1.
. Circular cladograms of the maximum likelihood phylogenetic inference of S/MUFA Elovl (a) and PUFA Elovl (b) from echinoderm species. H. pulcherrimus sequences are indicated by red dots in each leaf node. The fully labelled phylogram trees are provided in electronic supplementary material, figures S2 (S/MUFA Elovl) and S3 (PUFA Elovl).
Figure 2.
. Circular cladogram of the maximum likelihood phylogenetic inference of Fads from echinoderm species. H. pulcherrimus sequences are indicated by red dots in each leaf node. The fully labelled phylogram tree is provided in electronic supplementary material, figure S4.
Figure 3.
. Elovl6-like C isolated from H. pulcherrimus showed elongase activities towards various C18 MUFA and PUFA to produce the corresponding C20 products. (a) Gas chromatograms of FAME prepared from the transgenic yeast transformed with an empty pYES2 (control) or pYES2 containing the full-length ORF of H. pulcherrimus elovl6-like c. (b,c) Gas chromatograms of FAME prepared from the transgenic yeast transformed with pYES2 containing the full-length ORF of H. pulcherrimus elovl6-like c and grown in the presence of 18:3n-3 (b) and 18:4n-3 (c) indicated with an asterisk. Fatty acids are numbered as follows: 16:0 (1), 16:1n-7 (2), 18:0 (3), 18:1n-9 (4), 18:1n-7 (5), 20:1n-9 (6) and 20:1n-7 (7).
Figure 4.
.
H. pulcherrimus FadsA enables production of C20 non-methylene-interrupted dienoic fatty acids. Gas chromatograms of FAME prepared from the transgenic yeast transformed with pYES2 containing the full-length ORF of H. pulcherrimus fadsa and grown in the presence of 20:1n-9 (a) and 20:1n-7 (b) indicated with an asterisk. 18:1n-13 is a Δ5-desaturated product from 18:0. The yeast endogenous fatty acids are numbered as follows: 16:0 (1), 16:1n-7 (2), 18:0 (3), 18:1n-9 (4).
Figure 5.
. Biosynthetic pathways of various C20 PUFA in H. pulcherrimus. (a) The biosynthetic pathways of C20 dienoic NMI-FAs from C16 and C18 MUFA substrates. (b) The biosynthetic pathways of various C20 PUFA including physiologically important ARA (20:4n-6) and EPA (20:5n-3) as well as trienoic and tetraenoic NMI-FAs (20:3Δ5,11,14 and 20:4Δ5,11,14,17, respectively).
