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Rational reprogramming of fungal polyketide first-ring cyclization.

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Researchers engineered fungal polyketide synthases by altering active sites, reprogramming cyclization to create novel compounds. This work enables the biosynthesis of diverse chemical structures from natural precursors.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Natural Product Biosynthesis

Background:

  • Resorcylic acid and dihydroxyphenylacetic acid lactones are key pharmacophores with immune and heat shock activities.
  • Fungal polyketide biosynthesis involves iterative polyketide synthases (iPKSs), including nonreducing iPKSs (nrPKSs), which dictate product structure through cyclization.
  • Distinct fungal and bacterial folding modes in polyketide cyclization, catalyzed by product template (PT) domains or separate enzymes, lead to different structural outcomes.

Purpose of the Study:

  • To investigate the structural basis for the differing fungal and bacterial folding modes in polyketide biosynthesis.
  • To engineer hybrid enzymes to understand and control polyketide folding.
  • To enable the rational design of novel polyketide structures through directed biosynthesis.

Main Methods:

  • Construction and characterization of hybrid iterative polyketide synthases (iPKSs) combining fungal and bacterial domains.
  • Structure-guided engineering of the active site of a dehydrocurvularin nonreducing iPKS (nrPKS) using site-directed mutagenesis.
  • Structural and biochemical analysis of engineered enzymes and their unnatural products.

Main Results:

  • The fungal versus bacterial folding mode difference is transferable between enzymes, as demonstrated by hybrid iPKSs.
  • Three point mutations in the cyclization chamber of a dehydrocurvularin nrPKS PT domain were sufficient to switch the folding mode from bacterial to fungal.
  • Engineered enzymes produced novel polyketides with altered folding patterns, confirming the reprogramming of regiospecific aldol condensations.

Conclusions:

  • The folding mode of fungal polyketides can be rationally controlled by engineering the active site of the product template domain.
  • This study provides a foundation for the engineered biosynthesis of novel chemical diversity from unreduced polyketides.
  • Understanding and manipulating polyketide folding pathways opens new avenues for drug discovery and natural product synthesis.