title: Structural properties of metal-free apometallothioneins.
abstract: The metalated forms of metallothionein are well studied (particularly Zn-MT, Cu-MT and Cd-MT), but almost nothing is known about the chemical and structural properties of apometallothioneins despite their importance in initial metalation and subsequent demetalation. Electrospray ionization mass spectrometry was used to provide a detailed view of the structural properties of the metal-free protein. Mass spectra of Zn(7)-MT and apo-MT at pH 7 exhibit the same charge state distribution, indicating that apo-MT is tightly folded like the metallated protein, whereas apo-MT at pH 3 exhibits a charge state spectrum associated with unfolding or denaturation. Benzoquinone was used to modify the cysteines in the β-MT (9 Bq), and α-MT (11 Bq) fragments, and the full βα-MT (20 Bq) protein. ESI-MS showed that the overall volume and, therefore, the extent of folding for the modified proteins is similar to that of Zn-MT. Molecular modeling using MM3-MD methods provided the volume of each modified protein. The volumes of the partially modified proteins follow the same trend as the charge states, showing that ESI-MS is an excellent method with which to follow small changes in protein folding as a function of applied chemical stress. The data suggest that the structure of apo-βα-MT is more organized than previously considered.
authors.affiliation: Department of Biology, The University of Western Ontario, London, Ontario, Canada N6A 5B7.
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Summers
authors.forename: AnjanPreet K
authors.initials: AK
authors.lastname: Mahrok
authors.forename: Michael D M
authors.initials: MD
authors.lastname: Dryden
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Stillman
mesh_terms: D016227:Benzoquinones / Q000737:chemistry; D003545:Cysteine / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008668:Metallothionein / Q000737:chemistry*; D008670:Metals; D008958:Models, Molecular; D017510:Protein Folding; D017433:Protein Structure, Secondary; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D016227:Benzoquinones; D008670:Metals; C004532:quinone; D008668:Metallothionein; D003545:Cysteine