Cloning and functional characterization of a polyunsaturated fatty acid elongase in a marine bivalve noble scallop Chlamys nobilis Reeve

• An ELOVL-like gene was identified from the noble scallop Chlamys nobilis.
• The elongase was phylogenetically related to vertebrate ELOVL2 and ELOVL5.
• The elongase actively elongated C18 and C20, but not C22, PUFA substrates.
• The elongase showed preference to n-6 PUFAs.
• The elongase could actively elongate some MUFAs to some extent.

Enzymes that lengthen the carbon chain of polyunsaturated fatty acids (PUFAs) are keys to the biosynthesis of the highly unsaturated fatty acids. Here we report on the molecular cloning and functional characterization of a cDNA encoding a putative elongase of very long-chain fatty acids (ELOVL), a critical enzyme that catalyses the elongation of fatty acids (FAs) including PUFAs. The full length cDNA of the fatty acyl elongase from the noble scallop Chlamys nobilis was isolated by Rapid Amplification of cDNA Ends (RACE). The amplified cDNAs encoded a putative open reading frame (ORF) of 307 amino acids that contained histidine box HXXHH motif conserved in all elongases. Phylogenetic analysis suggested that the putative elongase was placed in the same group with ELOVL2 and ELOVL5, which had been demonstrated to be critical enzymes participating in the biosynthesis of PUFAs in vertebrates. Heterologous expression in yeast Saccharomyces cerevisiae demonstrated that the ORF encoded an elongase with the ability to lengthen n − 3 and n − 6 PUFA substrates with chain lengths of C18 and C20, exhibiting similar substrate specificities to vertebrate ELOVL5. Moreover, the noble scallop elongase could lengthen monounsaturated fatty acids to low activity, but not saturated fatty acids. The interesting point was that this elongase converted n − 6 PUFA substrates more efficiently than their homologous n − 3 substrates, suggesting that n − 6 PUFAs might have particular biological significance in C. nobilis.