ACTIVE-SITE GEOMETRY IN THE HIGH OXIDOREDUCTION POTENTIAL RUSTICYANINFROM THIOBACILLUS-FERROOXIDANS

Rusticyanin is a blue copper protein involved in the oxidation of iron catalyzed by Thiobacillus ferrooxidans. This protein is characterized by a high oxide-reduction potential and a high stability at low pH. T he three dimensional structure of this protein is still unknown and in order to investigate the geometric properties of the copper center wh ich could be correlated to the high oxide-reduction potential, we have studied rusticyanin by UV-Visible, EPR and NMR spectroscopies, at dif ferent pH values. Our results suggest that rusticyanin is stable betwe en pH 2 and pH 9 and that the copper center does not undergo significa nt geometric modifications in this pH range. Moreover, the copper atom could be buried more deeply in the protein than in other type I coppe r proteins and the atomic distance Cu-S(Met), one of the four bonds in volved in copper coordination, is probably shorter in rusticyanin than in other cupredoxins. These two properties of the copper site are exp ected to be responsible, in part, for the high oxide-reduction potenti al observed in rusticyanin. (C) 1994 Academic Press, Inc.