Structure of Nm23-H1 under oxidative conditions

Nm23‐H1/NDPK‐A, a tumour metastasis suppressor, is a multifunctional housekeeping enzyme with nucleoside diphosphate kinase activity. Hexameric Nm23‐H1 is required for suppression of tumour metastasis and it is dissociated into dimers under oxidative conditions. Here, the crystal structure of oxidized Nm23‐H1 is presented. It reveals the formation of an intramolecular disulfide bond between Cys4 and Cys145 that triggers a large conformational change that destabilizes the hexameric state. The dependence of the dissociation dynamics on the H2O2 concentration was determined using hydrogen/deuterium‐exchange experiments. The quaternary conformational change provides a suitable environment for the oxidation of Cys109 to sulfonic acid, as demonstrated by peptide sequencing using nanoUPLC‐ESI‐q‐TOF tandem MS. From these and other data, it is proposed that the molecular and cellular functions of Nm23‐H1 are regulated by a series of oxidative modifications coupled to its oligomeric states and that the modified cysteines are resolvable by NADPH‐dependent reduction systems. These findings broaden the understanding of the complicated enzyme‐regulatory mechanisms that operate under oxidative conditions.