In contrast to the toxic selectivity of some natural products that allow them to be used as antibiotics, fortuitous mainstays of human health and longevity, there are opposing, blunt toxicities by primitive mechanisms of action that overwhelm host defenses in preparation for systemic invasion. Fungi in particular can be pathogenic to animals and plants and use polyketide metabolites as virulence factors in these ways against their victims. Environmental toxins have detrimental effects on human health and must be closely monitored. That vigilance accounts for several $B/yr in losses to grain and nut crops and contaminated milk and meat destroyed. The aflatoxins are a paradigm among mycotoxins and occupy a central place in environmental toxicology. Hepatocarcinomas are the third most common cause of cancer death in the world. Hepatitis infections and dietary aflatoxin are major risk factors where clear epidemiological data correlate exposure to human disease. To the environmental carcinogen aflatoxin B1 can be added polyketide metabolites like T-2 toxin, zearalenone, fumonisin B, ochratoxin, patulin, citrinin and cercosporin. These secondary metabolites all derive from a family of fungal, polydomain enzymes called polyketide synthases (PKSs). They are fundamentally related to animal fatty acid synthases (FASs), but, unlike FASs, they synthesize reactive products that can undergo biosynthetic chemistry to a wide array of structural types. Many of the primitive toxins of pathogenic fungi arise from this versatile biosynthetic machinery. These enzymes have eluded investigation for years, especially compared to other types of PKSs, but the work of this lab in the last decade has made great inroads into this problem. These enzymes exhibit the unusual property of iterative catalysis where a small basis set of catalytic domains is reused multiple times but a fixed number of times to a specific, programmed end. This poorly understood catalytic behavior has been collectively called ?programming? and is the goal of this research effort to understand. Great strides have been made in the current grant period with dramatic technical advances to dissect and reassemble functional domains for biochemical and structural analysis that we intend to drive the Research Plan proposed. A comprehensive approach is advanced to proceed on three fronts: protein X-ray crystallography of individual and multiple domains from the polyketide synthases, mechanistic enzymology of PKS function, and synthetic biology and combinatorial enzymology of a library of catalytic domains to elicit further understanding of function and to carry out syntheses of new products.

Public Health Relevance

The aflatoxins and other fungal mycotoxins occupy a central place in environmental toxicology affecting both agriculture and human health. Iterative polyketide synthases initiate the biosynthesis of most of these natural products. Their functions are poorly understood, but understanding them is central to their control and the focus of this research.

Agency
National Institute of Health (NIH)
Type
Research Project (R01)
Project #
5R01ES001670-36
Application #
8662778
Study Section
Macromolecular Structure and Function E Study Section (MSFE)
Program Officer
Reinlib, Leslie J
Project Start
Project End
Budget Start
Budget End
Support Year
36
Fiscal Year
2014
Total Cost
Indirect Cost
Name
Johns Hopkins University
Department
Chemistry
Type
Schools of Arts and Sciences
DUNS #
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Barajas, Jesus F; Finzel, Kara; Valentic, Timothy R et al. (2016) Structural and Biochemical Analysis of Protein-Protein Interactions Between the Acyl-Carrier Protein and Product Template Domain. Angew Chem Int Ed Engl 55:13005-13009
Zhou, Jiawang; Outlaw, Victor K; Townsend, Craig A et al. (2016) Quenching of pH-Responsive Luminescence of a Benzoindolizine Sensor by an Ultrafast Hydrogen Shift. Chemistry 22:15212-15215
Newman, Adam G; Townsend, Craig A (2016) Molecular Characterization of the Cercosporin Biosynthetic Pathway in the Fungal Plant Pathogen Cercospora nicotianae. J Am Chem Soc 138:4219-28
Outlaw, Victor K; d'Andrea, Felipe B; Townsend, Craig A (2015) One-pot synthesis of highly substituted N-fused heteroaromatic bicycles from azole aldehydes. Org Lett 17:1822-5
Huitt-Roehl, Callie R; Hill, Eric A; Adams, Martina M et al. (2015) Starter unit flexibility for engineered product synthesis by the nonreducing polyketide synthase PksA. ACS Chem Biol 10:1443-9
Conradt, David; Schätzle, Michael A; Haas, Julian et al. (2015) New Insights into the Conversion of Versicolorin A in the Biosynthesis of Aflatoxin B1. J Am Chem Soc 137:10867-9
Newman, Adam G; Vagstad, Anna L; Storm, Philip A et al. (2014) Systematic domain swaps of iterative, nonreducing polyketide synthases provide a mechanistic understanding and rationale for catalytic reprogramming. J Am Chem Soc 136:7348-62
Outlaw, Victor K; Townsend, Craig A (2014) A practical route to substituted 7-aminoindoles from pyrrole-3-carboxaldehydes. Org Lett 16:6334-7
Townsend, Craig A (2014) Aflatoxin and deconstruction of type I, iterative polyketide synthase function. Nat Prod Rep 31:1260-5
Bruegger, Joel; Haushalter, Robert W; Haushalter, Bob et al. (2013) Probing the selectivity and protein·protein interactions of a nonreducing fungal polyketide synthase using mechanism-based crosslinkers. Chem Biol 20:1135-46

Showing the most recent 10 out of 41 publications