Macromolecular crowding amplifies allosteric regulation of T-Cell Protein Tyrosine Phosphatase.

T-Cell Protein Tyrosine Phosphatase (TC-PTP) is a negative regulator of T-Cell Receptor and oncogenic Receptor Tyrosine Kinase signaling and implicated in cancer and autoimmune disease. TC-PTP activity is modulated by an intrinsically disordered C-terminal region (IDR) and suppressed in cells under basal conditions. In vitro structural studies have shown that the IDR's dynamic reorganization around the catalytic domain, driven by electrostatic interactions, can lead to TC-PTP activity inhibition, however the process has not been studied in cells. Here, by assessing a mutant (KRKRPR mutated into EAAAPE, called TC45) with impaired tail-PTP domain interaction, we obtained evidence that the downmodulation of TC-PTP enzymatic activity by the IDR occurs in cells. However, we found that the regulation of TC-PTP by the IDR is only recapitulated in vitro when crowding polymers that mimic the intracellular environment are present in kinetic assays using a physiological phosphopeptide. Our FRET-based assays in vitro and in cells confirmed that the effect of the mutant correlates with an impairment of the intramolecular inhibitory remodeling of TC-PTP by the IDR. This work presents an early example of the allosteric regulation of a Protein Tyrosine Phosphatase being controlled by the cellular environment and provides a framework for future studies and targeting of TC-PTP function.