X-ray absorption studies of yeast copper metallothionein

The local structures of the metal sites in copper metallothionein from Saccharomyces cerevisiae have been investigated by x-ray absorption spectroscopy at the copper and sulfur K edges. Analysis of the EXAFS (extended x-ray absorption fine structure) data indicates that each copper is trigonally coordinated to sulfur at a distance of 2.23 A. Cu-Cu interactions at 2.7 and 3.9 A have also been tentatively identified. Sulfur K edge data are compatible with cysteinyl thiolates bridging each of the eight Cu(I) ions. The data support a model for the copper cluster in yeast metallothionein consisting of a Cu8S12 core. EXAFS data on two specifically engineered carboxyl-terminal truncated mutants reveal that the copper coordination in the mutants is similar to that observed in the wild-type protein.