Protein tyrosine phosphatase sigma (PTPσ) plays a vital role in neural development. The extracellular domain of PTPσ binds to various proteoglycans, which control the activity of 2 intracellular PTP domains (D1 and D2). To understand the regulatory mechanism of PTPσ, we carried out structural and biochemical analyses of PTPσ D1D2. In the crystal structure analysis of a mutant form of D1D2 of PTPσ, we unexpectedly found that the catalytic cysteine of D1 is oxidized to cysteine sulfenic acid, while that of D2 remained in its reduced form, suggesting that D1 is more sensitive to oxidation than D2. This finding contrasts previous observations on PTPα. The cysteine sulfenic acid of D1 was further confirmed by immunoblot and mass spectrometric analyses. The stabilization of the cysteine sulfenic
acid in the active site of PTP suggests that the formation of cysteine sulfenic acid may function as a stable intermediate
during the redox-regulation of PTPs.

Keywords: crystal structure, protein tyrosine phosphatase sigma, proteoglycan, redox regulation, sulfenic acid