Expression and characterization of manganese lipoxygenase of the rice blast fungus reveals prominent sequential lipoxygenation of α-linolenic acid

• The lipoxygenase (LOX) of Magnaporthe oryzae was partially cloned and expressed.
• The LOX was purified to homogeneity and contained catalytic manganese.
• 18:2n-6 was oxidized to 9S-, 11S-, and 13R-hydroperoxy metabolites.
• Metabolites were formed by suprafacial hydrogen abstraction and oxygenation.
• 18:3n-3 was sequentially oxidized to 9S,16S-dihydroperoxy compound as end product.

Magnaporthe oryzae causes rice blast disease and has become a model organism of fungal infections. M. oryzae can oxygenate fatty acids by 7,8-linoleate diol synthase, 10R-dioxygenase-epoxy alcohol synthase, and by a putative manganese lipoxygenase (Mo-MnLOX). The latter two are transcribed during infection. The open reading frame of Mo-MnLOX was deduced from genome and cDNA analysis. Recombinant Mo-MnLOX was expressed in Pichia pastoris and purified to homogeneity. The enzyme contained protein-bound Mn and oxidized 18:2n-6 and 18:3n-3 to 9S-, 11-, and 13R-hydroperoxy metabolites by suprafacial hydrogen abstraction and oxygenation. The 11-hydroperoxides were subject to β-fragmentation with formation of 9S- and 13R-hydroperoxy fatty acids. Oxygen consumption indicated apparent kcat values of 2.8 s−1 (18:2n-6) and 3.9 s−1 (18:3n-3), and UV analysis yielded apparent Km values of 8 and 12 μM, respectively, for biosynthesis of cis-trans conjugated metabolites. 9S-Hydroperoxy-10E,12Z,15Z-octadecatrienoic acid was rapidly further oxidized to a triene, 9S,16S-dihydroperoxy-10E,12Z,14E-octadecatrienoic acid. In conclusion, we have expressed, purified and characterized a new MnLOX from M. oryzae. The pathogen likely secretes Mo-MnLOX and phospholipases to generate oxylipins and to oxidize lipid membranes of rice cells and the cuticle.