Functional characterization of fatty acyl desaturase Fads2 and Elovl5 elongase in the Boddart’s goggle-eyed goby, Boleophthalmus boddarti (Gobiidae) suggest an incapacity for long-chain polyunsaturated fatty acid biosynthesis

Long-chain polyunsaturated fatty acid biosynthesis, a process to convert C18 polyunsaturated fatty acids to eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) or arachidonic acid (ARA) requires the concerted activities of two enzymes, the fatty acyl desaturase (Fads) and elongase (Elovl). This study highlights the cloning, functional characterisation and tissue expression pattern of a Fads and Elovl from the Boddarts goggle-eyed goby (Boleophthalmus boddarti), a mudskipper species widely distributed in the Indo-Pacific region. Phylogenetic analysis revealed that the cloned Fads and Elovl are clustered with other teleost Fads2 and Elovl5 orthologs, respectively. Interrogation of the genome of several mudskipper species, namely B. pectinirostris, Periophthalmus schlosseri and P. magnuspinnatus revealed a single Fads2 for each respective species while two elongases, Elovl5 and Elovl4 were detected. Using a heterologous yeast assay, the B. boddarti Fads2 was shown to possess low desaturation activity on C18 PUFA. In addition, there was no desaturation of C20 and C22 substrates. In comparison, the Elovl5 showed a wide range of substrate specificity, with capacity to elongate C18, C20 and C22 PUFA substrates. We identified an amino acid residue in the B. boddarti Elovl5 that affect the capacity to bind C22 PUFA substrate. Both genes are highly expressed in brain tissue. Among all tissues, DHA is highly concentrated in neuron-rich tissues while EPA is highly deposited in gills. Taken together, the results showed that due to disability of desaturation steps, B. boddarti is unable to biosynthesis LC-PUFA, relying on dietary intake to acquire these nutrients.