title: Crystal structure of Epiphyas postvittana takeout 1 with bound ubiquinone supports a role as ligand carriers for takeout proteins in insects.
abstract: Takeout (To) proteins are found exclusively in insects and have been proposed to have important roles in various aspects of their physiology and behavior. Limited sequence similarity with juvenile hormone-binding proteins (JHBPs), which specifically bind and transport juvenile hormones in Lepidoptera, suggested a role for To proteins in binding hydrophobic ligands. We present the first crystal structure of a To protein, EpTo1 from the light brown apple moth Epiphyas postvittana, solved in-house by the single-wavelength anomalous diffraction technique using sulfur anomalous dispersion, and refined to 1.3 angstroms resolution. EpTo1 adopts the unusual alpha/beta-wrap fold, seen only for JHBP and several mammalian lipid carrier proteins, a scaffold tailored for the binding and/or transport of hydrophobic ligands. EpTo1 has a 45 angstroms long, purely hydrophobic, internal tunnel that extends for the full length of the protein and accommodates a bound ligand. The latter was shown by mass spectrometry to be ubiquinone-8 and is probably derived from Escherichia coli. The structure provides the first direct experimental evidence that To proteins are ligand carriers; gives insights into the nature of endogenous ligand(s) of EpTo1; shows, by comparison with JHBP, a basis for different ligand specificities; and suggests a mechanism for the binding/release of ligands.
authors.affiliation: The Horticulture and Food Research Institute of New Zealand Limited (HortResearch), Private Bag 92169, Auckland 1142, New Zealand.
authors.forename: Cyril
authors.initials: C
authors.lastname: Hamiaux
authors.forename: Duncan
authors.initials: D
authors.lastname: Stanley
authors.forename: Dave R
authors.initials: DR
authors.lastname: Greenwood
authors.forename: Edward N
authors.initials: EN
authors.lastname: Baker
authors.forename: Richard D
authors.initials: RD
authors.lastname: Newcomb
mesh_terms: D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D057927:Hydrophobic and Hydrophilic Interactions; D019476:Insect Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008024:Ligands; D008969:Molecular Sequence Data; D009036:Moths / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014451:Ubiquinone / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D019476:Insect Proteins; D008024:Ligands; D014451:Ubiquinone