A Novel omega 3-Desaturase in the Deep Sea Giant Tubeworm Riftia pachyptila

摘要

One paradox of the trophic biochemistry of the deep sea giant tubeworm Riftia pachyptila, endemic to hydrothermal vent sites and nourished by polyunsaturated fatty acid (PUFA) deficiency chemolitoautotrophic sulfide-oxidizing bacteria, is the source of their PUFAs. Biosynthesis of PUFA starts with two precursors C18:2n-6 and C18:3n-3, which cannot be biosynthesized by most animals due to lack of omega 6- and omega 3-desaturase; thus, C18:2n-6 and C18:3n-3 are generally essential fatty acids for animals. Here, we characterized a gene derived from the R. pachyptila located by hydrothermal vent, which encoded a novel omega 3-desaturase (Rp3Fad). The gene was identified by searching the R. pachyptila transcriptome database using known omega 3-desaturases, and its predicted protein showed 37-45% identical to omega 3-desaturases of fungus and microalgae, and only 31% identitical to nematode Caenorhabditis elegans omega 3-desaturase. Expression in yeast Saccharomyces cerevisiae showed that the Rp3Fad could desaturate C18:2n-6 and C18:3n-6 into C18:3n-3 and C18:4n-3, respectively, displaying a Delta 15 activity similar to plant omega 3-desaturase, but it showed no activity towards C20 n-6 PUFA substrates, differing from the well-characterized C. elegans omega 3-desaturases Delta 5, Delta 6, Delta 8, and Delta 12 activity were also tested, resulting in no corresponding production. The function of omega 3-desaturase identified in R. pachyptila could produce C18:3n - 3 used in synthesis of n - 3 series PUFAs, suggesting an adaption to PUFA deficiency environment in deep sea hydrothermal vent.