Identification of proteins involved in intracellular copper metabolism: Low levels of a ≈48-kDa copper-binding protein in the brindled mouse model of menkes disease

Little is known about copper metabolism at the cellular level. The brindled mouse is an animal model of Menkes disease which is an inborn error of copper metabolism. Control and brindled mice were used to identify copper-binding proteins with possible roles in normal copper metabolism that are affected by the defect in the brindled mice. When ⁶⁴Cu-labeled hepatic or renal cytosols from control mice were applied to Mono Q or Superose columns, a ≈48-kDa protein coeluted with the protein fractions which contained the radiolabeled copper. Large decreases in copper binding were detected in these fractions from the brindled mice. The same column fractions which showed decreased copper binding showed large decreases in the levels of the ≈48-kDa protein. Decreased copper binding and ≈48-kDa protein were not simply secondary to the abnormal hepatic and renal copper levels that are found in the brindled mice since although their liver copper levels are low, their kidney copper levels are high. Elevated levels of an ≈80-kDa heat shock protein were also detected in the hepatic and renal cytosols from the brindled mice. Consistent with expression of the primary defect in both the liver and kidney, the levels of the ≈48- and ≈80-kDa proteins were affected similarly in both organs. Irrespective of how the low levels of the ≈48-kDa protein may be related to the basic defect in the brindled mice, the data are consistent with an important role for the ≈48-kDa protein in intracellular copper metabolism.