PUFA Biosynthesis Pathway in Marine Scallop Chlamys nobilis Reeve

Abstract

Long-chain polyunsaturated fatty acids (LC-PUFAs) are essential in important physiological processes. However, the endogenous PUFA biosynthesis pathway is poorly understood in marine bivalves. Previously, a fatty acyl desaturase (Fad) with Δ5 activity was functionally characterized and an elongase termed Elovl2/5 was reported to efficiently elongate 18:2n-6 and 18:3n-3 to 20:2n-6 and 20:3n-3 respectively in Chlamys nobilis. In this study, another elongase and another Fad were identified. Functional characterization in recombinant yeast showed that the newly cloned elongase can elongate 20:4n-6 and 20:5n-3 to C22 and C24, while the newly cloned scallop Fad exhibited a Δ8-desaturation activity, and could desaturate exogenously added PUFA 20:3n-3 and 20:2n-6 to 20:4n-3 and 20:3n-6 respectively, providing the first compelling evidence that noble scallop could de novo biosynthesize 20:5n-3 and 20:4n-6 from PUFA precursors though the "Δ8 pathway". No Δ6 or Δ4 activity was detected for this Fad. Searching against our scallop transcriptome database failed to find any other Fad-like genes, indicating that noble scallop might have limited ability to biosynthesize 22:6n-3. Interestingly, like previously characterized Elovl2/5, the two newly cloned genes showed less efficient activity toward n-3 PUFA substrates than their homologous n-6 substrates, resulting in a relatively low efficiency to biosynthesize n-3 PUFA, implying an adaption to marine environment.

Molecular Cloning and Functional Characterisation of a Polyunsaturated Fatty Acid Elongase in a Marine Bivalve <i>Crassostrea</i><i> </i><i>angulata</i>

“…The result is consistent to the previous study in the mollusks [4,27] and in the vertebrates [24,28].…”

“…Instead bivalves have been thought to obtain the PUFAs from their diets [30,31]. However, in the present study, the oyster was identified to have the ability to biosynthesize PUFAs by itself, and previous study in two mollusks of O. vulgaris [4] and C. nobilis [16] had the same findings, respectively. Therefore, we conclude that marine mollusks have the ability to biosynthesize PUFAs by themselves.…”

“…As the second largest Phylum in animal kingdom, mollusks have provided delicious and health food for human due to their enriched higher protein and PUFAs [23,25,26]. However, mechanism of their enrichment in PUFAs has not been clearly described, although there have been a few reports about biosynthesis PUFAs mechanism in an octopus [4,5] and a bivalve [27] in recent years.…”

“…Peaks 1-4 represent the main endogenous FAs of S. cerevisiae, namely C16:0 (1), C16:1n-7 (2), C18:0 (3) and C18:1n-9 (4). The remaining main additional peaks (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) correspond to the exogenously added FAs and the products of their elongation-C18:2n-6 (7), C20:2n-6 (8), C20:3n-6 (9), C22:3n-6 (10), C22:3n-6 (11), C20:4n-6 (12), C22:4n-6 (13), C18:3n-3 (14), C20:3n-3 (15), C20:5n-3 (16) and C22:5n-3 (17). Other minor peaks are 20:1n-9 (5) and 20:1n-7 (6), the latter two resulting from the elongation of 18:1n-9 and 18:1n-7.…”

“…In addition, Scapharca broughtoni and Mytilus edulis were reported to have the capabilities of de novo synthesis for some peculiar fatty acids (FAs) called nonmethylene interrupted fatty acids (NMIs) [14,15]. More importantly, in recent years, our lab has provided the first compelling evidence that C. nobilis can de novo biosynthesize 20:5n-3 and 20:4n-6 from PUFA precursors though the "Δ8 pathway" [16].…”