Protein disulfide isomerase, a multifunctional protein chaperone, shows copper-binding activity.
Protein disulfide isomerase (PDI) is a 55 kDa multifunctional protein of the endoplasmic reticulum (ER) involved in protein folding and isomerization. In addition to the chaperone and catalytic functions, PDI is a major calcium-binding protein of the ER. Although the active site of PDI has a similar motif CXXC to the Cu-binding motif in Wilson and Menkes proteins and in other copper chaperones, there has been no report on any metal-binding capability of PDI other than calcium binding. We present evidence that PDI is a copper-binding protein. In the absence of reducing agent freshly reduced PDI can bind a maximum of 4 mol of Cu(II) and convert to Cu(I). These bound Cu(I) are surface exposed as they can be competed readily by BCS reagent, a Cu(I) specific chelator. However, when the binding is performed using the mixture of Cu(II) and 1mM DTT, the total number of Cu(I) bound increases to 10 mol/mol, and it is slower to react with BCS, indicating a more protected environment. In both cases, the copper-bound forms of PDI exist as tetramers while apo-protein is a monomer. These findings suggest that PDI plays a role in intracellular copper disposition.
Department of Structural Biology and Biochemistry, The Research Institute of the Hospital for Sick Children, Toronto, Ont., Canada M5G 1X8.
Suree
S
Narindrasorasak
Ping
P
Yao
Bibudhendra
B
Sarkar
D001665:Binding Sites; D003300:Copper / Q000737:chemistry*; D004229:Dithiothreitol / Q000737:chemistry; D004789:Enzyme Activation; D018832:Molecular Chaperones / Q000737:chemistry*; D011485:Protein Binding; D019704:Protein Disulfide-Isomerases / Q000737:chemistry*
D018832:Molecular Chaperones; D003300:Copper; D019704:Protein Disulfide-Isomerases; D004229:Dithiothreitol