The neuronal adaptor protein X11 alpha interacts with the copper chaperonefor SOD1 and regulates SOD1 activity

The neuronal adaptor protein X11 alpha: participates in the formation of mu ltiprotein complexes and intracellular trafficking. It contains a series of discrete protein-protein interaction domains including two contiguous C-te rminal PDZ domains. We used the yeast two-hybrid system to screen for prote ins that interact with the PDZ domains of human X11 alpha, and we isolated a clone encoding domains II and III of the copper chaperone for Cu,Zn-super oxide dismutase-1 (CCS). The X11 alpha /CCS interaction was confirmed in co immunoprecipitation studies plus glutathione S-transferase fusion protein p ull-down assays and was shown to be mediated via PDZ2 of X11 alpha and a se quence within the carboxyl terminus of domain III of CCS. CCS delivers the copper cofactor to the antioxidant superoxide dismutase-1 (SOD1) enzyme and is required for its activity. Overexpression of X11 alpha inhibited SOD1 a ctivity in transfected Chinese hamster ovary cells which suggests that X11 alpha binding to CCS is inhibitory to SOD1 activation. X11 alpha also inter acts with another copper-binding protein found in neurons, the Alzheimer's disease amyloid precursor protein. Thus, X11 alpha may participate in coppe r homeostasis within neurons.