G-Protein Coupled Receptors (GPCR) sense extracellular signals and activate different Guanine nucleotide binding proteins (G-proteins) that have alpha, beta and gamma subunits. Upon activation, the alpha subunit of G-proteins dissociates from beta-gamma and the both are then free to regulate downstream effectors. G-protein beta-gamma complex, along with phosphatidylinositol 3,4,5-trisphosphate (PIP3), recruits the non-receptor Tyrosine-protein kinase BTK to the cell membrane. In the membrane, the G-protein beta-gamma complex binds to the catalytic domain of BTK and activates it. Active BTK is then released to the cytoplasm. Physiologically, BTK plays a key role in B lymphocyte development, differentiation and signalling.