Crystal structure of Epiphyas postvittana takeout 1 with bound ubiquinone supports a role as ligand carriers for takeout proteins in insects

J Biol Chem. 2009 Feb 6;284(6):3496-503. doi: 10.1074/jbc.M807467200. Epub 2008 Dec 10.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Carrier Proteins / chemistry*
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Crystallography, X-Ray
  • Hydrophobic and Hydrophilic Interactions
  • Insect Proteins / chemistry*
  • Insect Proteins / genetics
  • Insect Proteins / metabolism
  • Ligands
  • Molecular Sequence Data
  • Moths / chemistry*
  • Moths / genetics
  • Moths / metabolism
  • Protein Structure, Tertiary / physiology
  • Sequence Homology, Amino Acid
  • Substrate Specificity
  • Ubiquinone / chemistry*
  • Ubiquinone / genetics
  • Ubiquinone / metabolism

Substances

  • Carrier Proteins
  • Insect Proteins
  • Ligands
  • Ubiquinone

Associated data

  • GENBANK/EU834740
  • GENBANK/EU834741
  • GENBANK/EU834742
  • GENBANK/EU834743
  • PDB/3E8T
  • PDB/3E8W