 It also has a role in mast cell activation through the high-affinity IgE receptor.Btk contains a PH domain that binds phosphatidylinositol (3,4,5)-trisphosphate (PIP3).PIP3 binding induces Btk to phosphorylate phospholipase C, which in turn hydrolyzes PIP2, a phosphatidylinositol, into two second messengers, inositol triphosphate (IP3) and diacylglycerol (DAG), which then go on to modulate the activity of downstream proteins during B-cell signalling.