title: Autonomous folding of interdomain regions of a modular polyketide synthase.
abstract: Domains within the multienzyme polyketide synthases are linked by noncatalytic sequences of variable length and unknown function. Recently, the crystal structure was reported of a portion of the linker between the acyltransferase (AT) and ketoreductase (KR) domains from module 1 of the erythromycin synthase (6-deoxyerythronolide B synthase), as a pseudodimer with the adjacent ketoreductase (KR). On the basis of this structure, the homologous linker region between the dehydratase (DH) and enoyl reductase (ER) domains in fully reducing modules has been proposed to occupy a position on the periphery of the polyketide synthases complex, as in porcine fatty acid synthase. We report here the expression and characterization of the same region of the 6-deoxyerythronolide B synthase module 1 AT-KR linker, without the adjacent KR domain (termed DeltaN AT1-KR1), as well as the corresponding section of the DH-ER linker. The linkers fold autonomously and are well structured. However, analytical gel filtration and ultracentrifugation analysis independently show that DeltaN AT1-KR1 is homodimeric in solution; site-directed mutagenesis further demonstrates that linker self-association is compatible with the formation of a linker-KR pseudodimer. Our data also strongly indicate that the DH-ER linker associates with the upstream DH domain. Both of these findings are incompatible with the proposed model for polyketide synthase architecture, suggesting that it is premature to allocate the linker regions to a position in the multienzymes based on the solved structure of animal fatty acid synthase.
authors.affiliation: Department of Biochemistry, University of Cambridge, UK.
authors.forename: Carsten D
authors.initials: CD
authors.lastname: Richter
authors.forename: David A
authors.initials: DA
authors.lastname: Stanmore
authors.forename: Ricardo N
authors.initials: RN
authors.lastname: Miguel
authors.forename: Martin C
authors.initials: MC
authors.lastname: Moncrieffe
authors.forename: Lucky
authors.initials: L
authors.lastname: Tran
authors.forename: Suzanne
authors.initials: S
authors.lastname: Brewerton
authors.forename: Filip
authors.initials: F
authors.lastname: Meersman
authors.forename: R William
authors.initials: RW
authors.lastname: Broadhurst
authors.forename: Kira J
authors.initials: KJ
authors.lastname: Weissman
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D048630:Polyketide Synthases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017510:Protein Folding; D017434:Protein Structure, Tertiary / Q000235:genetics; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D040681:Structural Homology, Protein
chemical_list: D029968:Escherichia coli Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins; D048630:Polyketide Synthases