Abstract: The invention relates to a method of identifying any protein tyrosine phosphatase (PTP) that undergoes reversible modification of PTP active site invariant cysteine within a cell, such that the phosphatase is transiently protected from irreversible active site invariant cysteine-directed PTP inactivating agents. Methods related to regulation of PTPs by reactive oxygen species (ROS) in a cellular environment are provided. Multiple PTPs are shown to be reversibly oxidized and inactivated following treatment of cells with H2O2 or with physiological stimuli that promote ROS formation, and inhibition of PTP function is shown to contribute to ROS-induced mitogenesis. Transient oxidation of the PTP catalytic site invariant cysteine is exploited in methods to identify which of multiple candidate PTPs are components of a given biological signal transduction pathway, without a requirement for first specifically purifying any particular candidate PTP.

Abstract: The invention relates in part to screening assays for identifying agents that alter the interaction between a protein tyrosine phosphatase (PTP) and its tyrosine phosphorylated polypeptide substrate, using fluorescence energy signals generated by detectably labeled substrates. Assays are provided in certain embodiments, including high throughput screening assays, wherein candidate agents are screened by fluorescence polarization for their ability to influence (i) binding of substrate trapping mutant PTPs to substrates, or (ii) dephosphorylation of tyrosine phosphorylated substrates by PTPs.

Abstract: Methods and compositions useful for protein tyrosine phosphatases (PTPs) are disclosed. Peptides are provided which, in one aspect, are useful as substrates for the determination of PTP activity. In contrast to the current approaches, such peptides provide a general substrate for which variations in PTP enzymatic activity due to the assay are minimized. The present invention also discloses methods for determining the presence or amount of PTP. Because of the increased sensitivity of the methods, PTPs can be detected in situations where only limiting amounts of sample, e.g., tissue extracts or immunoprecipitates, are available.