Multiple interactions between receptor protein-tyrosine phosphatase (RPTP) α and membrane-distal protein-tyrosine phosphatase domains of various RPTPs

Receptor protein-tyrosine phosphatase (RPTP) alpha belongs to the large family of receptor protein-tyrosine phosphatases containing two tandem phosphatase domains. Most of the catalytic activity is retained in the first, membrane-proximal domain (RPTP alpha-D1), and little is known about the function of the second, membrane distal domain (RPTP alpha-D2). We investigated whether proteins bound to RPTP alpha using the two-hybrid system and found that the second domain of RPTP sigma interacted with the juxtamembrane domain of RPTP alpha, We confirmed this interaction by co-immunoprecipitation experiments. Furthermore, RPTP alpha not only interacted with RPTP sigma-D2 but also with RPTP alpha-D2, LAR-D2, RPTP delta-D2, and RPTP mu-D2, members of various RPTP subfamilies, although with different affinities. In the yeast two-hybrid system and in glutathione S-transferase pull-down assays, we show that the RPTP-D2s interacted directly with the wedge structure of RPTP alpha-D1 that has been demonstrated to be involved in inactivation of the RPTP alpha-D1/RPTP alpha-D1 homodimer, The interaction was specific because the equivalent wedge structure in LAR was unable to interact with RPTP alpha-D2 or LAR-D2. In vitro, we show that other interaction sites exist as well, including the C terminus of RPTP alpha-D2. The observation that RPTP alpha, but not LAR, bound to multiple RPTP-D2s with varying affinities suggests a specific mechanism of cross-talk between RPTPs that may regulate their biological function.