Structural basis of negative regulation of thioredoxin by thioredoxin-interacting protein

Abstract

TXNIP has a large number of TRX-dependent and -independent functions in many biological systems. In the TRX-dependent manner, TXNIP, as a negative regulator of TRX, modulates the redox system by binding to TRX and inhibiting its function. Thus, elucidation of regulatory mechanism in the TRX-TXNIP system will improve our understanding of how TRX behaves in cells and whole organisms, both under normal conditions and in human disease. Together with coimmunoprecipitation assays and NMR experiment results, crystallo-graphic results provide insight into the molecular basis of the negative regulation of TRX by TXNIP. Disulfide switching event is necessary for binding to TRX and inhibiting its activity. The interaction between TRX and TXNIP molecules causes the disulfide bond switching from interprotomer disulfide bond between Cys63 and Cys247 to interdomain Cys63-Cys190 disulfide bond and intermolecular TXNIP Cys247-TRX Cys32 disulfide bond. This disulfide switching event results in different structural rearrangement from those of arrestin family. The intermolecular disulfide bond in the TRX-TXNIP complex is susceptible to the level of oxidative stress such as ROS. This mode of disulfide switching, revealed here for the first time to our knowledge, provides the key insight into the negative regulation of TRX by TXNIP.