title: Evidence that a novel thioesterase is responsible for polyketide chain release during biosynthesis of the polyether ionophore monensin.
abstract: Polyether ionophores, such as monensin A, are known to be biosynthesised, like many other antibiotic polyketides, on giant modular polyketide synthases (PKSs), but the intermediates and enzymes involved in the subsequent steps of oxidative cyclisation remain undefined. In particular there has been no agreement on the mechanism and timing of the final polyketide chain release. We now report evidence that MonCII from the monensin biosynthetic gene cluster in Streptomyces cinnamonensis, which was previously thought to be an epoxide hydrolase, is a novel thioesterase that belongs to the alpha/beta-hydrolase structural family and might catalyse this step. Purified recombinant MonCII was found to hydrolyse several thioester substrates, including an N-acetylcysteamine thioester derivative of monensin A. Further, incubation with a hallmark inhibitor of such enzymes, phenylmethanesulfonyl fluoride, led to inhibition of the thioesterase activity and to the accumulation of an acylated form of MonCII. These findings require a reassessment of the role of other enzymes implicated in the late stages of polyether ionophore biosynthesis.
authors.affiliation: The University Chemical Laboratory, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.
authors.forename: Barbara M
authors.initials: BM
authors.lastname: Harvey
authors.forename: Hui
authors.initials: H
authors.lastname: Hong
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Jones
authors.forename: Zoë A
authors.initials: ZA
authors.lastname: Hughes-Thomas
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Goss
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Heathcote
authors.forename: Victor M
authors.initials: VM
authors.lastname: Bolanos-Garcia
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kroutil
authors.forename: James
authors.initials: J
authors.lastname: Staunton
authors.forename: Peter F
authors.initials: PF
authors.lastname: Leadlay
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Spencer
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D020134:Catalytic Domain; D004228:Dithionitrobenzoic Acid / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics; D017353:Gene Deletion; D018942:Macrolides / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D008970:Molecular Weight; D008985:Monensin / Q000031:analogs & derivatives / Q000096:biosynthesis*; D010664:Phenylmethylsulfonyl Fluoride / Q000737:chemistry; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry; D013302:Streptomyces / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D013869:Thiolester Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D018942:Macrolides; D011993:Recombinant Fusion Proteins; D010664:Phenylmethylsulfonyl Fluoride; D008985:Monensin; D004228:Dithionitrobenzoic Acid; D013869:Thiolester Hydrolases