Abstract
Leucocyte adhesion receptor integrin CD11aCD18 and the transmembrane receptor-like protein tyrosine phosphatase (RPTP) CD45 mediate immune synapse formation and signalling during antigen presentation. Previous cocapping studies on human naïve T cells demonstrate an interaction between CD11aCD18 and CD45. CD45 cross-linking also has an effect on the ligand-binding activity of CD11aCD18. However, the mode of interaction between CD11aCD18 and CD45 remains unclear. Herein, yeast two-hybrid analysis identified a partial CD45 cytoplasmic tail interacting with that of CD11a. The CD45 cytoplasmic tail comprises a membrane proximal (Mp) region, protein tyrosine phosphatase domain 1 (D1), spacer, D2, and carboxyl terminus. CD45 Mp-D1 was found to be the main interacting region for the CD11a cytoplasmic tail. In contrast, the full-length CD45 cytoplasmic tail interacted weakly with that of CD11a. It has been reported that CD45 Mp-D1 but not the full-length cytoplasmic tail forms a homodimer whose enzymatic activity is inhibited. Our in vitro binding and enzymatic assays showed that the homodimeric CD45 cytoplasmic tail interacts with that of CD11a. The biological function of CD45 dimerization and its association with CD11a remains to be investigated.