Resonant x-ray scattering and absorption for the global and local structures of Cu-modified metallothioneins in solution

Biophys J. 2009 Jul 22;97(2):609-17. doi: 10.1016/j.bpj.2009.05.004.

Abstract

With Cd and Zn metal ions removed from the native rabbit-liver metallothionein upon unfolding, Cu-modified metallothioneins (Cu-MTs) were obtained during refolding in solutions containing Cu(I) or Cu(II) ions. X-ray absorption near-edge spectroscopic results confirm the respectively assigned oxidation states of the copper ions in Cu(I)-MT and Cu(II)-MT. Global and local structures of the Cu-MTs were subsequently characterized by anomalous small-angle x-ray scattering (ASAXS) and extended x-ray absorption fine structure. Energy-dependent ASAXS results indicate that the morphology of Cu(II)-MT resembles that of the native MT, whereas Cu(I)-MT forms oligomers with a higher copper content. Both dummy-residue simulation and model-shape fitting of the ASAXS data reveal consistently rodlike morphology for Cu(II)-MT. Clearly identified Cu-S, Cu-O, and Cu-Cu contributions in the extended x-ray absorption fine structure analysis indicate that both Cu(I) and Cu(II) ions are bonded with O and S atoms of nearby amino acids in a four-coordination environment, forming metal clusters smaller than metal thiolate clusters in the native MT. It is demonstrated that a combination of resonant x-ray scattering and x-ray absorption can be particularly useful in revealing complementary global and local structures of metalloproteins due to the atom specific characteristics of the two techniques.

MeSH terms

  • Absorption
  • Animals
  • Apoproteins / chemistry
  • Apoproteins / metabolism
  • Copper / chemistry*
  • Copper / metabolism*
  • Metallothionein / chemistry*
  • Metallothionein / metabolism*
  • Models, Molecular
  • Oxidation-Reduction
  • Protein Conformation
  • Protein Denaturation
  • Protein Renaturation
  • Rabbits
  • Scattering, Small Angle
  • Solutions
  • X-Ray Diffraction*

Substances

  • Apoproteins
  • Solutions
  • Copper
  • Metallothionein