title: Tricarballylic ester formation during biosynthesis of fumonisin mycotoxins inFusarium verticillioides.
abstract: Fumonisins are agriculturally important mycotoxins produced by the maize pathogenFusarium verticillioides.The chemical structure of fumonisins contains two tricarballylic esters, which are rare structural moieties and important for toxicity. The mechanism for the tricarballylic ester formation is not well understood.FUM7gene ofF. verticillioideswas predicted to encode a dehydrogenase/reductase, and when it was deleted, the mutant produced tetradehydro fumonisins (DH4-FB). MS and NMR analysis of DH4-FB1indicated that the esters consist of aconitate with a 3'-alkene function, rather than a 2'-alkene function. Interestingly, the purified DH4-FB1eventually yielded three chromatographic peaks in HPLC. However, MS revealed that the metabolites of the three peaks all had the same mass as the initial single-peak DH4-FB1. The results suggest that DH4-FB1can undergo spontaneous isomerization, probably including bothcis-transstereoisomerization and 3'- to 2'-ene regioisomerization. In addition, whenFUM7was expressed inEscherichia coliand the resulting enzyme, Fum7p, was incubated with DH4-FB, no fumonisin with typical tricarballylic esters was formed. Instead, new fumonisin analogs that probably contained isocitrate and/or oxalosuccinate esters were formed, which reveals new insight into fumonisin biosynthesis. Together, the data provided both genetic and biochemical evidence for the mechanism of tricarballylic ester formation in fumonisin biosynthesis.
authors.affiliation: Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588, USA ; School of Pharmaceutical Sciences, Shandong University, Jinan 250100, China.
authors.forename: Yaoyao
authors.initials: Y
authors.lastname: Lia
authors.affiliation: Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588, USA.
authors.forename: Lili
authors.initials: L
authors.lastname: Lou
authors.affiliation: Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588, USA.
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Cerny
authors.affiliation: National Center for Agriculture Utilization Research, ARS-USDA, 1815 North University Street, Peoria, IL 61604, USA.
authors.forename: Robert A E
authors.initials: RA
authors.lastname: Butchko
authors.affiliation: National Center for Agriculture Utilization Research, ARS-USDA, 1815 North University Street, Peoria, IL 61604, USA.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Proctor
authors.affiliation: School of Pharmaceutical Sciences, Shandong University, Jinan 250100, China.
authors.forename: Yuemao
authors.initials: Y
authors.lastname: Shen
authors.affiliation: School of Pharmaceutical Sciences, Shandong University, Jinan 250100, China.
authors.forename: Liangcheng
authors.initials: L
authors.lastname: Du
keywords: Fusarium verticillioides; biosynthesis; fumonisins; mycotoxins