Bruton's tyrosine kinase

• OMIM: 300300
• UniProt: Q06187

Bruton's tyrosine kinase ( BTK ) is an enzyme found in vertebrates, which catalyses the phosphorylation of certain proteins. Therefore, there is a kinase. It belongs to the tyrosine kinases of the Tec family that is predominantly expressed in B cells. BTK has important functions in mediating B- cell receptor signal into the cell. A mutation in the BTK gene of man is the cause of so-called Bruton's syndrome ( XLA ).

Construction

The Bruton tyrosine kinase consists of a PH domain at the N -terminus, followed by a TH domain ( Tec homology ), an SH3 domain, an SH2 domain and a C -terminal kinase domain. The TH domain consists in turn of a BH domain ( Btk homology ) and one or two proline-rich regions.

Activation

The first step in the activation of Btk is recruiting to the plasma membrane by the PH domain, which binds to phosphatidylinostiol -3 ,4,5- trisphosphate ( PIP3 ). PIP3 is a product of PI3- kinase. Simultaneously, the adapter protein BLNK is important for the recruitment of Btk to the membrane and thus to the B-cell receptor. The activity of Btk in B cells is presumably on the kinases Syk and Lyn.

Function

An important function of the activation of Btk PLCγ2. Btk phosphorylates the tyrosines 753 and 759 here in PLCγ2 what these enabled. In addition, Btk recruits phosphatidylinositol -4 -phosphate 5 kinase ( PIP5K ) to the plasma membrane. PIP5K in turn synthesizes the important PLCγ2 substrate phosphatitylinsitol -4 ,5- bisphosphate ( PIP2 ) from PIP.

A point mutation in Btk in mice leads to the fact that the kinase is not directed to the plasma membrane. These mice are called xid mice ( X -linked immunodeficient ).