Intermolecular transfer of copper ions from the CopC protein of Pseudomonas syringae. Crystal structures of fully loaded CuICuII forms

Abstract

CopC is a small soluble protein expressed in the periplasm of Pseudomonas syringae pathovar tomato as part of its copper resistance response (cop operon). Equilibrium competition reactions confirmed two separated binding sites with high affinities for CuI (10-7 ≥ KD ≥ 10-13 M) and CuII (KD = 10-13(1) M), respectively. While CuI-CopC was converted cleanly by O2 to CuII-CopC, the fully loaded form CuICu II-CopC was stable in air. Variant forms H1F and H91F exhibited a lower affinity for CuII than does the wild-type protein while variant E27G exhibited a higher affinity. Cation exchange chromatography detected each of the four different types of intermolecular copper transfer reactions possible..