Recombinant Fusarium sporotrichioides Trichodiene synthase (TRI5)

Trichodiene synthase; part of the core gene cluster that mediates the biosynthesis of trichothecenes, a very large family of chemically related bicyclic sesquiterpene compounds acting as mycotoxins, including T2-toxin. The biosynthesis of trichothecenes begins with the cyclization of farnesyl diphosphate to trichodiene and is catalyzed by the trichodiene synthase TRI5. Trichodiene undergoes a series of oxygenations catalyzed by the cytochrome P450 monooxygenase TRI4. TRI4 controls the addition of four oxygens at C-2, C-3, C-11, and the C-12, C-13-epoxide to form the intermediate isotrichotriol. Isotrichotriol then undergoes a non-enzymatic isomerization and cyclization to form isotrichodermol. During this process, the oxygen at the C-2 position becomes the pyran ring oxygen and the hydroxyl group at C-11 is lost. More complex type A trichothecenes are built by modifying isotrichodermol through a series of paired hydroxylation and acetylation or acylation steps. Isotrichodermol is converted to isotrichodermin by the acetyltransferase TRI101. TRI101 encodes a C-3 transacetylase that acts as a self-protection or resistance factor during biosynthesis and that the presence of a free C-3 hydroxyl group is a key component of Fusarium trichothecene phytotoxicity. A second hydroxyl group is added to C-15 by the trichothecene C-15 hydroxylase TRI11, producing 15-decalonectrin, which is then acetylated by TRI3, producing calonectrin. A third hydroxyl group is added at C-4 by the cytochrome P450 monooxygenase TRI13, converting calonectrin to 3,15-diacetoxyspirpenol, which is subsequently acetylated by the acetyltransferase TRI7. A fourth hydroxyl group is added to C-8 by the cytochrome P450 monooxygenase TRI1, followed by the addition of an isovaleryl moiety by TRI16. Finally, the acetyl group is removed from the C-3 position by the trichothecene C-3 esterase TRI8 to produce T-2 toxin.