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Figure 1 | BMC Genomics

Figure 1

From: Comparative genome sequencing reveals chemotype-specific gene clusters in the toxigenic black mold Stachybotrys

Figure 1

The two toxin chemotypes of Stachybotrys. Both atranones and satratoxins are terpenoid secondary metabolites thought to derive from the primary metabolite farnesyl pyrophosphate (FPP). Box colors indicate each class of molecule and its specific secondary metabolite precursors: blue for atranones, green for simple trichothecenes, and pink for macrocyclic trichothecenes, which include satratoxins. Atranones are diterpenoids thought to originate from cyclization of geranylgeranyl pyrophosphate to form dolabellane, which has an eleven-membered ring [11]. Shown are the structures of all atranones solved by Hinkley et al.[11], as well as types of enzymes capable of catalyzing the two postulated reactions in the pathway. Trichothecenes are sesquiterpenoids that are products of FPP cyclization. The pathway of trichodermol biosynthesis from FPP is known experimentally [12, 13], but there are no experimental data regarding biosynthesis pathways of satratoxins or other trichodermol derivatives. Shown is a conceptual pathway adapted from [14] and references therein. It integrates results from several trichothecene producers. Enzymes shown have been functionally characterized from Fusarium (Tri5) or Trichoderma (Tri4 and Tri11). Trichodiol is shown to represent several intermediates that undergo both enzymatic hydroxylation and spontaneous rearrangement to form trichodermol, which is the first molecule shown that contains the trichothecene skeleton, i.e., the tricyclic ring 12,13-epoxytrichothec-9-ene (EPT). In Fusarium, trichodermol is not observed. Instead, the pathway after trichodiol diverges into a series of products substituted at C-3 of EPT. There are two known trichoverrols (A and B) and two known trichoverrins (A and B), but the respective pairs differ only in the stereochemistry of the C-4 side chain. The satratoxin F/G skeleton is shown as representative of satratoxins, and roridin E as representative of roridins. Omitted for brevity are the verrucarins (double arrow between roridins and satratoxins).

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