Intracellular metal binding and redox behavior of human DJ-1

DJ-1 is a conserved, ubiquitous protein associated to a large number of intracellular processes. Human DJ-1 has been linked to several pathologies, including hereditary forms of Parkinson's disease, cancer, and amyotrophic lateral sclerosis. Several cytoprotective functions of DJ-1 have been reported, however, its actual mechanisms of action remain elusive. In vitro, DJ-1 has been shown to bind zinc and copper(II) at its active site, which contains a conserved cysteine (C106), and copper(I) at a different binding site. C106 is essential to DJ-1 function, and is easily oxidized upon oxidative stress. Here, we investigated the metal-binding- and redox properties of DJ-1 in living human cells by in-cell NMR. Intracellular DJ-1 is surprisingly free from interactions with any other cellular components and as such is clearly detectable by NMR. Metal-bound forms of DJ-1 were not observed upon treating the cells with excess zinc or copper. No copper binding was observed when co-expressing DJ-1 with the copper chaperone for superoxide dismutase 1 (SOD1). Co-expression of DJ-1 with SOD1 itself did not promote copper binding to SOD1, excluding a previously suggested function of DJ-1 as a copper chaperone. Overall, our data do not support the role of DJ-1 as a metalloprotein. Conversely, oxidative treatment to the cells caused the complete and selective oxidation of C106 to sulfinic acid, consistent with the reported role of DJ-1 as a redox sensor.