BTK
Bruton's tyrosine kinase (abbreviated Btk or BTK) also known as tyrosine-protein kinase BTK is an enzyme that in humans is encoded by the BTK gene. BTK plays a crucial role in B cell maturation as well as 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.