title: Thioesterase-like role for fungal PKS-NRPS hybrid reductive domains.
abstract: Fungal reduced polyketides possess diverse structures exploring a broad region of chemical space despite their synthesis by very similar enzymes. Many fungal polyketides are capped by diverse amino acid-derived five-membered rings, the tetramic acids and related pyrrolidine-2-ones. The known tetramic acid synthetase enzymes in fungi contain C-terminal reductive (R) domains that were proposed to release reduced pyrrolidine-2-one intermediates en route to the tetramic acids. To determine the enzymatic basis of pyrrolidine-2-one diversity, we overexpressed equisetin synthetase (EqiS) R domains and analyzed their reactivity with synthetic substrate analogs. We show that the EqiS R domain does not perform a reducing function and does not bind reducing cofactors. Instead, the EqiS R catalyzes a Dieckmann condensation, with an estimated kcat approximately 15 s(-1). This role differs from the redox reactions normally catalyzed by short chain dehydrogenase/reductase superfamily enzymes.
authors.affiliation: Department of Medicinal Chemistry, University of Utah, 30 South 2000 East Rm 201, Salt Lake City, Utah 84112, USA.
authors.forename: James W
authors.initials: JW
authors.lastname: Sims
authors.forename: Eric W
authors.initials: EW
authors.lastname: Schmidt
mesh_terms: D019755:Carbon-Carbon Lyases / Q000737:chemistry; D020134:Catalytic Domain; D004950:Esterases / Q000737:chemistry*; D005658:Fungi / Q000737:chemistry*; D007700:Kinetics; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010453:Peptide Synthases / Q000737:chemistry*; D048630:Polyketide Synthases / Q000737:chemistry*; D017510:Protein Folding; D017434:Protein Structure, Tertiary / Q000502:physiology; D011760:Pyrrolidinones / Q000138:chemical synthesis / Q000737:chemistry; D013379:Substrate Specificity; D013764:Tetrahydronaphthalenes / Q000138:chemical synthesis / Q000737:chemistry
chemical_list: D011760:Pyrrolidinones; D013764:Tetrahydronaphthalenes; C024509:equisetin; D048630:Polyketide Synthases; D004950:Esterases; D019755:Carbon-Carbon Lyases; D010453:Peptide Synthases