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Related Experiment Videos

Structure-guided programming of polyketide chain-length determination in chalcone synthase.

J M Jez1, M E Bowman, J P Noel

  • 1Structural Biology Laboratory, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, California 92037, USA.

Biochemistry
|December 6, 2001
PubMed
Summary
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Mutating chalcone synthase (CHS) at position 256 alters polyketide chain length by changing active site cavity volume. This reveals how CHS enzymes diversify products while maintaining activity.

Area of Science:

  • Biochemistry
  • Enzymology
  • Structural Biology

Background:

  • Chalcone synthase (CHS) is a type III polyketide synthase (PKS) crucial for synthesizing diverse polyketides.
  • CHS catalyzes the formation of a tetraketide via sequential condensation reactions involving malonyl-CoA and a starter molecule.
  • The active site cavity volume is hypothesized to influence polyketide chain length determination in type III PKS.

Purpose of the Study:

  • To investigate the role of active site cavity volume at position 256 in chalcone synthase (CHS) activity and product specificity.
  • To determine how altering the side chain volume at residue 256 affects polyketide chain extension and cyclization.

Main Methods:

  • Site-directed mutagenesis of CHS at Gly256 to alanine (G256A), valine (G256V), leucine (G256L), and phenylalanine (G256F).

Related Experiment Videos

  • Functional characterization of CHS mutants using p-coumaroyl-CoA as a starter molecule.
  • X-ray crystallography to determine the structural basis of altered enzymatic activity in the mutants.

    • Main Results:

    • CHS mutants G256A and G256V showed increased production of tetraketide lactone compared to wild-type CHS.
    • Mutants G256L and G256F, with further reduced cavity volume, produced higher levels of styrylpyrone bis-noryangonin.
    • Structural analysis confirmed that substitutions at position 256 decrease active site cavity size without major backbone conformational changes.

    Conclusions:

    • The side chain volume at position 256 directly influences the number of condensation reactions and intermediate conformations in CHS.
    • Modifications at residue 256 can lead to rapid diversification of CHS product specificity.
    • Evolutionary changes in side chain volume at position 256 may allow related CHS-like enzymes to diversify products without losing catalytic efficiency.