Molecular Insights into Lipoxygenases in Diatoms Based on Structure Prediction: a Pioneering Study on Lipoxygenases Found in Pseudo-nitzschia arenysensis and Fragilariopsis cylindrus.

Diatoms produce a variety of oxylipins which are oxygenated polyunsaturated fatty acids and are involved in chemical defense and intercellular communication, among other roles. Although the chemistry of diatom oxylipins has long been studied, the enzymes involved in their production, in particular lipoxygenase (LOX), which catalyzes the initial reaction of the synthesis, have not been discovered in diatom genomes. Recently, diatom LOXs were found in two species, Pseudo-nitzschia arenysensis (PaLOX) and Fragilariopsis cylindrus (FcLOX); however, the enzymology of these LOXs is largely unknown. In this review article, we discuss the potential functions of the diatom LOXs based on previously reported structures of LOXs derived from various organisms other than diatoms. Since the structures of PaLOX and FcLOX have not yet been solved, we discussed their functions, such as regio- and stereospecificities, on the basis of their structures predicted using a computational tool based on deep learning technology. Both diatom LOXs were predicted to conserve common core domains with relatively wide substrate-binding pockets. The stereo-determinant residues in PaLOX and FcLOX suggest S specificity. We assume that the highly conserved common core domain can be a clue to reveal unidentified lox genes from the accumulated diatom genome information with the aid of high-throughput structure prediction tools and structure-based alignment tools in the near future.