title: Structural basis for macrolactonization by the pikromycin thioesterase.
abstract: Polyketides are a class of biologically active microbial and plant-derived metabolites that possess a high degree of structural and functional diversity and include many human therapeutics, among them anti-infective and anti-cancer drugs, growth promoters and anti-parasitic agents. The macrolide antibiotics, characterized by a glycoside-linked macrolactone, constitute an important class of polyketides, including erythromycin and the natural ketolide anti-infective agent pikromycin. Here we describe new mechanistic details of macrolactone ring formation catalyzed by the pikromycin polyketide synthase thioesterase domain from Streptomyces venezuelae. A pentaketide phosphonate mimic of the final pikromycin linear chain-elongation intermediate was synthesized and shown to be an active site affinity label. The crystal structures of the affinity-labeled enzyme and of a 12-membered-ring macrolactone product complex suggest a mechanism for cyclization in which a hydrophilic barrier in the enzyme and structural restraints of the substrate induce a curled conformation to direct macrolactone ring formation.
authors.affiliation: Life Sciences Institute, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, Michigan 48109-2216, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: Akey
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Kittendorf
authors.forename: John W
authors.initials: JW
authors.lastname: Giraldes
authors.forename: Robert A
authors.initials: RA
authors.lastname: Fecik
authors.forename: David H
authors.initials: DH
authors.lastname: Sherman
authors.forename: Janet L
authors.initials: JL
authors.lastname: Smith
mesh_terms: D001665:Binding Sites / Q000187:drug effects; D001713:Biphenyl Compounds / Q000737:chemistry / Q000494:pharmacology; D002384:Catalysis; D003460:Crystallization; D003500:Cyclization; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D018942:Macrolides / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008968:Molecular Conformation; D063065:Organophosphonates / Q000737:chemistry / Q000494:pharmacology; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013237:Stereoisomerism; D013302:Streptomyces / Q000201:enzymology; D013329:Structure-Activity Relationship; D013869:Thiolester Hydrolases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D001713:Biphenyl Compounds; D004791:Enzyme Inhibitors; D018942:Macrolides; D063065:Organophosphonates; D013869:Thiolester Hydrolases; C003145:picromycin