Fig. 2. cis-homophilic interactions of PTPRT are reinforced through tyrosine phosphorylation by Fyn tyrosine kinase. (A, B) PTPRT appears to induce synaptic formation through trans-homophilic interactions with each other, and cis-heterophilic interaction with neuroligin and neurexin. (C) Synaptic molecules could be recruited to PTPRT by neuroligin and neurexin. Activated PTPRT dephosphorylates many synaptic substrates and regulates synaptic functions. (D) When Fyn tyrosine kinase phophorylates tyrosine 912 of PTPRT, cis-homophilic interaction is induced, PTPRT activity is inhibited, and synaptic formation is attenuated. (F) In the crystal structure of PTPRK/RPTPκ (pdb code: 2c7s), tyrosine 892 is equivalent to tyrosine 912 fin PTPRT. Left, overall view of PTPRK D1 catalytic domain. The wedge moiety is shown as cyan, while the rest of the molecule is shown as yellow. The catalytic cysteine and the tyrosine residue are colored green. Right, close-up view of PTPRK near tyrosine 892. The residues involving the close contacts with tyrosine 892 are shown as sticks.