1u0m

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spinqualitylabelsall models 1u0m, resolution 2.22Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Crystal Structure of 1,3,6,8-Tetrahydroxynaphthalene Synthase (THNS) from Streptomyces coelicolor A3(2): a Bacterial Type III Polyketide Synthase (PKS) Provides Insights into Enzymatic Control of Reactive Polyketide Intermediates

Overview

In bacteria, a structurally simple type III polyketide synthase (PKS), known as 1,3,6,8-tetrahydroxynaphthlene synthase (THNS) catalyzes the, iterative condensation of five CoA-linked malonyl units to form a, pentaketide intermediate. THNS subsequently catalyzes dual intramolecular, Claisen and aldol condensations of this linear intermediate to produce the, fused ring tetrahydroxynaphthalene (THN) skeleton. The type III, PKS-catalyzed polyketide extension mechanism, utilizing a conserved, Cys-His-Asn catalytic triad in an internal active site cavity, is fairly, well understood. However, the mechanistic basis for the unusual production, of THN and dual cyclization of its malonyl-primed pentaketide is obscure., Here we present the first bacterial type III PKS crystal structure, that, of Streptomyces coelicolor THNS, and identify by mutagenesis, structural, modeling, and chemical analysis the unexpected catalytic participation of, an additional THNS-conserved cysteine residue in facilitating, malonyl-primed polyketide extension beyond the triketide stage. The, resulting new mechanistic model, involving the use of additional cysteines, to alter and steer polyketide reactivity, may generally apply to other PKS, reaction mechanisms, including those catalyzed by iterative type I and II, PKS enzymes. Our crystal structure also reveals an unanticipated novel, cavity extending into the "floor" of the traditional active site cavity, providing the first plausible structural and mechanistic explanation for, yet another unusual THNS catalytic activity: its previously inexplicable, extra polyketide extension step when primed with a long acyl starter. This, tunnel allows for selective expansion of available active site cavity, volume by sequestration of aliphatic starter-derived polyketide tails, and, further suggests another distinct protection mechanism involving, maintenance of a linear polyketide conformation.

About this Structure

1U0M is a Single protein structure of sequence from Bacteria with 15P and GOL as ligands. Full crystallographic information is available from OCA.

Reference

Crystal structure of a bacterial type III polyketide synthase and enzymatic control of reactive polyketide intermediates., Austin MB, Izumikawa M, Bowman ME, Udwary DW, Ferrer JL, Moore BS, Noel JP, J Biol Chem. 2004 Oct 22;279(43):45162-74. Epub 2004 Jul 20. PMID:15265863

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