Fig. 2.

BTK’s structure and interactions. BTK contains 659 amino acids and five domains from the N-terminus to the C-terminus, including an amino-terminal pleckstrin homology domain (PH domain), a proline-rich TEC homology (TH) domain, the SRC homology domains SH2 and SH3 domains, and a catalytic domain. Phosphorylation of the Y551 and Y223 sites is necessary for the activation of BTK. Cys481 residues on the catalytic domain are the main targets for the approved BTK inhibitors