Abstract

The presence of two protein-tyrosine phosphatase (PTP) domains is a striking feature in most transmembrane receptor PTPs (RPTPs). The function of the generally inactive membrane-distal PTP domain (RPTP-D2) is unknown. Here we report that an intramolecular interaction between the spacer region (Sp) and the C-terminus in RPTP prohibited intermolecular interactions. Interestingly, stress factors such as H₂O₂, UV and heat shock induced reversible, free radical-dependent, intermolecular interactions between RPTP and RPTP-SpD2, suggesting an inducible switch in conformation and binding. The catalytic site cysteine of RPTP-SpD2, Cys723, was required for the H₂O₂ effect on RPTP. H₂O₂ induced a rapid, reversible, Cys723-dependent conformational change in vivo, as detected by fluorescence resonance energy transfer, with cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP) flanking RPTP-SpD2 in a single chimeric protein. Importantly, H₂O₂ treatment stabilized RPTP dimers, resulting in inactivation. We propose a model in which oxidative stress induces a conformational change in RPTP-D2, leading to stabilization of RPTP dimers, and thus to inhibition of RPTP activity.