Open AccessZinc transfer potentials of the α- and β-clusters of metallothionein are affected by domain interactions in the whole molecule
Author(s) -
Lijuan Jiang,
Milan Vašák,
Bert L. Vallée,
Wolfgang Maret
Publication year - 2000
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.97.6.2503
Subject(s) - zinc , chemistry , metallothionein , titration , molecule , stereochemistry , cysteine , reactivity (psychology) , crystallography , binding constant , metalloprotein , chelation , binding site , inorganic chemistry , biochemistry , enzyme , organic chemistry , medicine , alternative medicine , pathology
The α- and β-polypeptides of human metallothionein (isoform 2), obtained by chemical synthesis, were converted into their respective zinc/thiolate clusters, and each domain was investigated separately. Proton titration data for the N-terminal β-domain fit a simple model with three ionizations of the same apparent pKa value of 4.9 and a collective binding constant for zinc of 5 × 10−12 M at pH 7.0. The zinc cluster in the C-terminal α-domain is more stable than that in the β-domain. Its pH titration is also more complex, indicating at least two classes of zinc sites with different affinities. The whole molecule is stabilized with regard to the individual domains. Chemical modification implicates lysine side chains in both the stabilization of the β-domain cluster and the mutual stabilization of the domains in the whole molecule. The two zinc clusters also differ in the reactivity of their cysteine sulfurs and their potential to donate zinc to an acceptor molecule dependent on its type and characteristics. The isolated β-domain cluster reacts faster with Ellman's reagent and is a better zinc donor toward zinc-depleted sorbitol dehydrogenase than is the isolated α-domain cluster, whereas the reverse is observed when a chelating agent is the zinc acceptor. Thus, although each cluster assembles independently of the other, the cumulative properties of the individual domains do not suffice to describe metallothionein either structurally or functionally. The two-domain structure of the whole molecule is important for its interaction with ligands and for control of its reactivity and overall conformation.