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catalytic domain of tyrosine-protein phosphatase non-receptor type 22 Tyrosine-protein phosphatase non-receptor type 22 (PTPN22), also called lymphoid phosphatase (LyP), PEST-domain phosphatase (PEP), or hematopoietic cell protein-tyrosine phosphatase 70Z-PEP, belongs to the family of classical tyrosine-specific protein tyrosine phosphatases (PTPs). PTPs (EC 3.1.3.48) catalyze the dephosphorylation of phosphotyrosine peptides. PTPN22 is expressed in hematopoietic cells and it functions as a key regulator of immune homeostasis by inhibiting T-cell receptor signaling through the direct dephosphorylation of Src family kinases (Lck and Fyn), ITAMs of the TCRz/CD3 complex, and other signaling molecules. Mutations in the PTPN22 gene are associated with multiple connective tissue and autoimmune diseases including type 1 diabetes mellitus, rheumatoid arthritis, and systemic lupus erythematosus. PTPN22 contains an N-terminal catalytic PTP domain and four proline-rich regions at the C-terminus.
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