title: Sticky swinging arm dynamics: studies of an acyl carrier protein domain from the mycolactone polyketide synthase.
abstract: Type I modular polyketide synthases (PKSs) produce polyketide natural products by passing a growing acyl substrate chain between a series of enzyme domains housed within a gigantic multifunctional polypeptide assembly. Throughout each round of chain extension and modification reactions, the substrate stays covalently linked to an acyl carrier protein (ACP) domain. In the present study we report on the solution structure and dynamics of an ACP domain excised from MLSA2, module 9 of the PKS system that constructs the macrolactone ring of the toxin mycolactone, cause of the tropical disease Buruli ulcer. After modification of apo ACP with 4'-phosphopantetheine (Ppant) to create the holo form, (15)N nuclear spin relaxation and paramagnetic relaxation enhancement (PRE) experiments suggest that the prosthetic group swings freely. The minimal chemical shift perturbations displayed by Ppant-attached C3 and C4 acyl chains imply that these substrate-mimics remain exposed to solvent at the end of a flexible Ppant arm. By contrast, hexanoyl and octanoyl chains yield much larger chemical shift perturbations, indicating that they interact with the surface of the domain. The solution structure of octanoyl-ACP shows the Ppant arm bending to allow the acyl chain to nestle into a nonpolar pocket, whereas the prosthetic group itself remains largely solvent exposed. Although the highly reduced octanoyl group is not a natural substrate for the ACP from MLSA2, similar presentation modes would permit partner enzyme domains to recognize an acyl group while it is bound to the surface of its carrier protein, allowing simultaneous interactions with both the substrate and the ACP.
authors.affiliation: Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, U.K. Crescendo Biologics Ltd, Meditrina Building 260, Babraham Research Campus, Cambridge CB22 3AT, U.K.
authors.forename: Steven
authors.initials: S
authors.lastname: Vance
authors.affiliation: Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, U.K. Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 5QY, U.K.
authors.forename: Olga
authors.initials: O
authors.lastname: Tkachenko
authors.affiliation: Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, U.K.
authors.forename: Ben
authors.initials: B
authors.lastname: Thomas
authors.affiliation: Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, U.K.
authors.forename: Mona
authors.initials: M
authors.lastname: Bassuni
authors.affiliation: Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, U.K.
authors.forename: Hui
authors.initials: H
authors.lastname: Hong
authors.affiliation: Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, U.K.
authors.forename: Daniel
authors.initials: D
authors.lastname: Nietlispach
authors.affiliation: Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, U.K. rwb1002@cam.ac.uk.
authors.forename: William
authors.initials: W
authors.lastname: Broadhurst
mesh_terms: D000213:Acyl Carrier Protein / Q000737:chemistry* / Q000378:metabolism; D018942:Macrolides / Q000737:chemistry* / Q000378:metabolism; D019911:Mycobacterium ulcerans; D048630:Polyketide Synthases / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D000213:Acyl Carrier Protein; D018942:Macrolides; C117218:mycolactone; D048630:Polyketide Synthases
keywords: 4′-phosphopantetheine; NMR spectroscopy; acyl carrier protein; mycolactone; type I polyketide synthase