Identification of a Δ4-desaturase from the microalga Ostreococcus lucimarinus

Very long chain PUFA (VLCPUFA) like DHA are essential and health-beneficial components of the human diet. Due to a shortfall in VLCPUFA supply, research is ongoing to establish VLCPUFA production in heterologous systems like for example oilseed plants. For this purpose it is crucial to identify the required enzymes from primary producers of VLCPUFA. Here, we describe a cDNA from the microalga Ostreococcus lucimarinus coding for a Delta 4-fatty acid desaturase. It exhibits a cytochrome b(5) domain fused to its amino terminus and three histidine boxes that are typically found in front-end desaturases. Heterologous expression of the partly codon-optimized version of the cDNA in yeast revealed that the encoded protein catalyzes the desaturation of (n-3)- as well as (n-6)-substrates with a preference for VLCPUFA. In yeast it localized at the endoplasmic reticulum (ER) membrane and analysis of the product distribution into different lipid classes suggested that the enzyme most likely acts in a lipid-dependent manner. Practical applications: The identified Delta 4-desaturase may be useful for the production of DHA in transgenic oleaginous organisms like annual oilseed crops.