Protein GAPT (also known as Growth-factor Receptor-Bound protein 2 (GRB2)-binding adaptor protein, transmembrane) belongs to a class of transmembrane (TM) adaptor proteins that couple antigen receptor engagement to downstream signalling cascades in lymphocytes []. Expressed in B cells and myeloid cells, GAPT negatively regulates B-cell proliferation following stimulation through the B-cell receptor; it may also play an important role in the proper maintenance of marginal zone B-cells [].GAPT has an extracellular domain, a TM domain, and a cytoplasmic tail with multiple GRB2-binding motifs; it constitutively associates with GRB2 SH3 domains via a proline-rich region []. Its cytosolic domain contains 7 tyrosine residues (4 of them within GRB2-binding motifs), and 2 cysteines in the juxta-membrane region, which may be palmitoylated [].
