Time‐dependent inhibitors of Lymphoid Tyrosine Phosphatase

Lymphoid tyrosine phosphatase (Lyp) is a 105‐kDa Class I protein tyrosine phosphatase (PTP) encoded by the PTPN22 gene and is expressed exclusively in immune cells. Lyp is known to potently inhibit T cell receptor signaling by dephosphorylating several substrates, including the Src family kinases Lck and Fyn, ZAP70, and TCRzeta. Lyp has recently emerged as a key player in a range of human autoimmune diseases including type I diabetes, rheumatoid arthritis, systemic lupus erythematosus, Graves’ and Addison's disease. The basis for Lyp's involvement in autoimmune disease is a single nucleotide polymorphism in PTPN22 that results in an amino acid change from Arg620 to Trp620 in the non‐catalytic C‐terminal domain of Lyp. The result is an increase in phosphatase activity although the molecular basis is not well understood. To reverse the pathogenic effect of this Lyp‐W620 variant, small molecule inhibitors are desired for therapeutic treatment of autoimmune disorders. The objective of the work presented here is to develop small molecules that can function as Michael acceptors to inactivate Lyp activity in vitro. Kinetic analysis has shown that these inhibitors inhibit Lyp in a time‐ and concentration‐dependent manner under pseudo‐first order conditions, and that Lyp activity does not return after extensive dialysis. Furthermore, the compounds appear to bind in the active site, as inhibition is reduced by co‐incubation of the enzyme with a known competitive inhibitor of PTPs. Further characterization is underway to gain more information on the mechanism of inhibition and selectivity among other members of the PTP family.