title: Structure of a specialized acyl carrier protein essential for lipid A biosynthesis with very long-chain fatty acids in open and closed conformations.
abstract: The solution nuclear magnetic resonance (NMR) structures and backbone (15)N dynamics of the specialized acyl carrier protein (ACP), RpAcpXL, from Rhodopseudomonas palustris, in both the apo form and holo form modified by covalent attachment of 4'-phosphopantetheine at S37, are virtually identical, monomeric, and correspond to the closed conformation. The structures have an extra α-helix compared to the archetypical ACP from Escherichia coli, which has four helices, resulting in a larger opening to the hydrophobic cavity. Chemical shift differences between apo- and holo-RpAcpXL indicated some differences in the hinge region between α2 and α3 and in the hydrophobic cavity environment, but corresponding changes in nuclear Overhauser effect cross-peak patterns were not detected. In contrast to the NMR structures, apo-RpAcpXL was observed in an open conformation in crystals that diffracted to 2.0 Å resolution, which resulted from movement of α3. On the basis of the crystal structure, the predicted biological assembly is a homodimer. Although the possible biological significance of dimerization is unknown, there is potential that the resulting large shared hydrophobic cavity could accommodate the very long-chain fatty acid (28-30 carbons) that this specialized ACP is known to synthesize and transfer to lipid A. These structures are the first representatives of the AcpXL family and the first to indicate that dimerization may be important for the function of these specialized ACPs.
authors.affiliation: Department of Chemistry and Biochemistry, Northeast Structural Genomics Consortium, Miami University, Oxford, Ohio 45056, United States. ramelota@miamiOH.edu
authors.forename: Theresa A
authors.initials: TA
authors.lastname: Ramelot
authors.forename: Paolo
authors.initials: P
authors.lastname: Rossi
authors.forename: Farhad
authors.initials: F
authors.lastname: Forouhar
authors.forename: Hsiau-Wei
authors.initials: HW
authors.lastname: Lee
authors.forename: Yunhuang
authors.initials: Y
authors.lastname: Yang
authors.forename: Shuisong
authors.initials: S
authors.lastname: Ni
authors.forename: Sarah
authors.initials: S
authors.lastname: Unser
authors.forename: Scott
authors.initials: S
authors.lastname: Lew
authors.forename: Jayaraman
authors.initials: J
authors.lastname: Seetharaman
authors.forename: Rong
authors.initials: R
authors.lastname: Xiao
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Acton
authors.forename: John K
authors.initials: JK
authors.lastname: Everett
authors.forename: James H
authors.initials: JH
authors.lastname: Prestegard
authors.forename: John F
authors.initials: JF
authors.lastname: Hunt
authors.forename: Gaetano T
authors.initials: GT
authors.lastname: Montelione
authors.forename: Michael A
authors.initials: MA
authors.lastname: Kennedy
mesh_terms: D000213:Acyl Carrier Protein / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D008050:Lipid A / Q000096:biosynthesis* / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012241:Rhodopseudomonas / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000213:Acyl Carrier Protein; D001426:Bacterial Proteins; D008050:Lipid A