Characterization of Elovl2/5 in abalone Haliotis discus hannai Ino

Elongation of very long-chain fatty acids protein (Elovl) plays vital role in the biosynthesis of long chain polyunsaturated fatty acids (LC-PUFA) in aquatic animals. However, there is very limited research on Elovl in abalone. In this study, an elongase gene encoding 303 amino acids was found to exhibit higher homology with the Elovl2/5 sequences of mollusks (60 %) than the Elovl5 of fish and mammals (about 43.30 %). Heterologous expression in yeast showed that abalone Elovl could efficiently catalyze the extension of C18:3n-3, C18:3n-6 and C18:4n-3, moderately elongate C18:2n-6, C20:4n-6 and C20:5n-3 to corresponding products. However, it has extremely weak ability to extend C20:3n-6 and C20:4n-3 and no affinity for C22 PUFA. Phylogenetic tree analysis showed that the sequence of abalone Elovl is closely related to Elovl2/5 of the cuttlefish (Sepia officinalis) and octopus (Octopus vulgaris). Tissue distribution revealed that the Elovl was highly expressed in female and male gonads, moderately in hepatopancreas, and minimally in other tested tissues. The expression levels of Elovl in hepatopancreas of abalone fed 50 % FO and 75 % FO diets were significantly higher than that in the 100 % FO control group. And no significant differences were found in the expressions of 0 % FO, 25 % FO and control groups. The EPA in 75 % FO group is significantly higher than those of other groups. This study provides the first systematic characterization of the dual substrate specificity of Elovl in abalone, bridging a critical knowledge gap in the evolutionary and functional investigation of elongases within gastropods.