Biosynthesis of Mycotoxin Fumonisins: Characterization of Enzymes for Vicinal Diol and Tricarballylic Ester Formation

University Of Nebraska-Lincoln, Lincoln NE

Investigators

Abstract

Fumonisins are small molecular toxins, which are produced by several fungal pathogens, including Fusarium verticillioides. This fungus is a widespread contaminant of corn and maize-derived products. Despite the importance of fumonisins, the biochemical and molecular basis for the production of these toxins remains largely uncharacterized. The overall goal of the research is to understand the molecular mechanistic details of the individual biosynthetic steps that lead to the formation of fumonisins in F. verticillioides. The goal of this project is to characterize two groups of enzymes that introduce two unusual functionalities, a vicinal diol and tricarballylic esters, on the carbon backbone of fumonisins. The introduction of these functional groups is crucial for the maturation of mycotoxins, without which the metabolites are not biologically active. Two objectives are set forth for the project: (1) to express and characterize oxidation enzymes that directly introduce the vicinal diol on the linear carbon chain of the toxins and (2) to determine the chemical reactions catalyzed by a unique nonribosomal peptide synthetase complex that converts the diol into two tricarballylic esters. The introduction of a vicinal diol by the direct oxidation of two neighboring carbons represents a new approach to functionalize the carbon chain, whereas the ester bond formation catalyzed by the complex is the first example that a nonribosomal peptide synthetase catalyzes a carbon-oxygen, instead of the typical carbon-nitrogen, bond formation. The research has several significant broader impacts. First and foremost, graduate and undergraduate students will receive extensive training in the area of natural product biosynthesis. In addition, research-based knowledge obtained from the project will enrich and enhance the development of a new course in natural product biosynthesis at the University of Nebraska-Lincoln. Furthermore, the project will promote strong collaborations between a synthetic chemist and a biochemist, which will help provide critical knowledge regarding widespread mechanisms utilized by pathogenic fungi and help promote public awareness of mycotoxins. This is especially significant in an agricultural state like Nebraska, one of the nation's major corn producers.