Intermolecular Transfer of Copper Ions from the CopC Protein of Pseudomonas syringae. Crystal Structures of Fully Loaded CuICuII Forms
详细信息 查看全文
- 作者：Lianyi Zhang ; Melissa Koay ; Megan J. Maher ; Zhiguang Xiao ; and Anthony G. Wedd
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：May 3, 2006
- 年：2006
- 卷：128
- 期：17
- 页码：5834 - 5850
- 全文大小：523K
- 年卷期：v.128,no.17(May 3, 2006)
- ISSN：1520-5126
文摘
CopC is a small soluble protein expressed in the periplasm of Pseudomonas syringae pathovartomato as part of its copper resistance response (cop operon). Equilibrium competition reactions confirmedtwo separated binding sites with high affinities for CuI (10-7 
s/entities/ge.gif"> KD s/entities/ge.gif"> 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 CuICuII-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 eachof the four different types of intermolecular copper transfer reactions possible between wild type and variantforms: CuI site to CuII site; CuII site to CuI site; CuI site to CuI site; CuII site to CuII site. The availability ofan unoccupied site of higher affinity induced intermolecular transfer of either CuI or CuII in the presence ofO2 while buffering concentrations of cupric ion at sub-picomolar levels. Crystal structures of two crystalforms of wild-type CuICuII-CopC and of the apo-H91F variant demonstrate that the core structures of themolecules in the three crystal forms are conserved. However, the conformations of the amino terminus (aCuII ligand) and the two copper-binding loops (at each end of the molecule) differ significantly, providingthe structural lability needed to allow transfer of copper between partners, with or without change of oxidationstate. CopC has the potential to interact directly with each of the four cop proteins coexpressed to theperiplasm.