Abstract
Microalgae tend to accumulate lipids as an energy storage material in the specific organelle, oleosomes. Current studies have demonstrated that lipids derived from microalgal oleosomes are a promising source of biofuels, while the oleosome formation mechanism has not been fully elucidated. Oleosome-associated proteins have been identified from several microalgae to elucidate the fundamental mechanisms of oleosome formation, although understanding their functions is still in infancy. Recently, we discovered a diatom-oleosome-associated-protein 1 (DOAP1) from the oleaginous diatom, Fistulifera solaris JPCC DA0580. The DOAP1 sequence implied that this protein might be transported into the endoplasmic reticulum (ER) due to the signal sequence. To ensure this, we fused the signal sequence to green fluorescence protein. The fusion protein distributed around the chloroplast as like a meshwork membrane structure, indicating the ER localization. This result suggests that DOAP1 could firstly localize at the ER, then move to the oleosomes. This study also demonstrated that the DOAP1 signal sequence allowed recombinant proteins to be specifically expressed in the ER of the oleaginous diatom. It would be a useful technique for engineering the lipid synthesis pathways existing in the ER, and finally controlling the biofuel quality.
Highlights
With an increased demand for a sustainable energy supply, biofuel production has attracted much attention
It would be reasonable to consider that translation of diatom-oleosome-associated-protein 1 (DOAP1) starts from the most forward start codon in the RNA-seq supporting region, the start codon was predicted to locate 93 bp-downstream from the transcription initiation site (Supplementary Figure S1)
Sequence features of DOAP1 were examined with the SignalP [27] and InterProScan algorisms, and it was predicted that DOAP1 contains an N-terminal signal sequence, as well as quinonprotein alcohol dehydrogenase-like superfamily (IPR011047, ranging from Q18 to P184)
Summary
With an increased demand for a sustainable energy supply, biofuel production has attracted much attention. Several oleaginous microalgae can accumulate triacylglycerol (TAG) in high level as a form of the oleosome ( known as oil body), and such promising oil producers have been intensively studied to understand the TAG biosynthesis [2,3,4,5,6]. The proteomic approach is expected to identify the novel protein machineries directly participating in the oleosome formation, which conventional pathway analysis can hardly address. It leads to the elucidation of the biological mechanism for oleosome development, and can provide promising targets of genetic engineering for the purpose of oil production improvements. The oleosome-associated proteins have been studied in only a few microalgae [12,13,14,15,16,17,18,19]
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