Attempting to Create a Pathway to 15-Deacetylcalonectrin with Limited Accumulation in Cultures of Mutants: Insight into Trichothecene Biosynthesis Machinery.

The compound 15-deacetylcalonectrin (15-deCAL) is a common pathway intermediate in the biosynthesis of trichothecenes. This tricyclic intermediate is metabolized to calonectrin (CAL) by trichothecene 15--acetyltransferase encoded by . Unlike other trichothecene pathway gene mutants, the Δ mutant produces lower amounts of the knocked-out enzyme's substrate 15-deCAL, and instead, accumulates higher quantities of earlier bicyclic intermediate and shunt metabolites. Furthermore, evolutionary studies suggest that may play a role in shaping the chemotypes of trichothecene-producing strains. To better understand the functional role of Tri3p in biosynthesis and evolution, we aimed to develop a method to produce 15-deCAL by using transgenic strains derived from a trichothecene overproducer. Unfortunately, introducing mutant , encoding a catalytically impaired but structurally intact acetylase, did not improve the low 15-deCAL production level of the Δ deletion strain, and the bicyclic products continued to accumulate as the major metabolites of the active-site mutant. These findings are discussed in light of the enzyme responsible for 15-deCAL production in trichothecene biosynthesis machinery. To efficiently produce 15-deCAL, we tested an alternative strategy of using a CAL-overproducing transformant. By feeding a crude CAL extract to a strain that was isolated in this study and capable of specifically deacetylating C-15 acetyl, 15-deCAL was efficiently recovered. The substrate produced in this manner can be used for kinetic investigations of this enzyme and its possible role in chemotype diversification.