Redox regulation of dimerization of the receptor protein-tyrosine phosphatases RPTPα, LAR, RPTPμ and CD45

Whether dimerization is a general regulatory mechanism of receptor protein-tyrosine phosphatases (RPTPs) is a subject of debate. Biochemical evidence demonstrates that RPTP alpha and cluster of differentiation (CD)45 dimerize. Their catalytic activity is regulated by dimerization and structural evidence from RPTP alpha supports dimerization-induced inhibition of catalytic activity. The crystal structures of CD45 and leukocyte common antigen related (LAR) indicate that dimerization would result in a steric clash. Here, we investigate dimerization of four RPTPs. We demonstrate that LAR and RPTP mu dimerized constitutively, which is likely to be due to their ectodomains. To investigate the role of the cytoplasmic domain in dimerization we generated RPTP alpha ectodomain (ED alpha)/RPTP chimeras and found that - similarly to native RPTP alpha- oxidation stabilized their dimerization. Limited tryptic proteolysis demonstrated that oxidation induced conformational changes in the cytoplasmic domains of these RPTPs, indicating that the cytoplasmic domains are not rigid structures, but rather that there is flexibility. Moreover, oxidation induced changes in the rotational coupling of dimers of full length ED alpha/RPTP chimeras in living cells, which were largely dependent on the catalytic cysteine in the membrane-distal protein-tyrosine phosphatase domain of RPTP alpha and LAR. Our results provide new evidence for redox regulation of dimerized RPTPs.