title: Resonant x-ray scattering and absorption for the global and local structures of Cu-modified metallothioneins in solution.
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.
authors.affiliation: Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan.
authors.forename: Meiyi
authors.initials: M
authors.lastname: Li
authors.forename: Yu-Shan
authors.initials: YS
authors.lastname: Huang
authors.forename: U-Ser
authors.initials: US
authors.lastname: Jeng
authors.forename: I-Jui
authors.initials: IJ
authors.lastname: Hsu
authors.forename: Yewchung
authors.initials: Y
authors.lastname: Sermon Wu
authors.forename: Ying-Huang
authors.initials: YH
authors.lastname: Lai
authors.forename: Chiu-Hun
authors.initials: CH
authors.lastname: Su
authors.forename: Jyh-Fu
authors.initials: JF
authors.lastname: Lee
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Chia-Ching
authors.initials: CC
authors.lastname: Chang
mesh_terms: D000042:Absorption; D000818:Animals; D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D003300:Copper / Q000737:chemistry* / Q000378:metabolism*; D008668:Metallothionein / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011487:Protein Conformation; D011489:Protein Denaturation; D020673:Protein Renaturation; D011817:Rabbits; D053838:Scattering, Small Angle; D012996:Solutions; D014961:X-Ray Diffraction
chemical_list: D001059:Apoproteins; D012996:Solutions; D003300:Copper; D008668:Metallothionein