Fig. 4. The 17th FNIII repeat of VE-PTP is sufficient for binding to VE-cadherin. (A) Schematic representation of the domain structure of full-length VE-PTP (dark grey), full-length JAM (light grey) and three chimeric fusion proteins containing an N-terminal Flag-tag and various parts of VE-PTP and JAM: the cytoplasmic tail of VE-PTP and the extracellular and transmembrane domain of JAM (JAM–VE1), the cytoplasmic and transmembrane domain of VE-PTP fused to the extracellular domain of JAM (JAM–VE2) or the extracellular 17th FNIII repeat of VE-PTP and the cytoplasmic and transmembrane domain of JAM (VE–JAM). (B) COS cells were transfected with truncated VE-cadherin lacking its cytoplasmic tail (VE-cad EC, lanes 1–4) and, in addition, co-transfected with one of the three different VE-PTP– JAM fusion proteins (lanes 1–3). Proteins immunoprecipitated with anti-Flag antibodies were immunoblotted first with anti-VE-cadherin antibodies (top), and then the same filters were re-probed with anti-Flag antibodies (middle). Total cell lysates were immunoblotted with anti-VE-cadherin antibodies (bottom). Note that truncated VE-cadherin was only co-precipitated with the VE-PTP–JAM fusion protein that included the 17th FNIII repeat of VE-PTP (lane 3). The asterisk marks the IgG heavy chain detected by the secondary antibody. Molecular mass markers (in kDa) are shown on the left.