Nonreceptor tyrosine kinase Structure

Structure and General Function of Nonreceptor Tyrosine Kinases... 

Permanent or transient association with subcellular structures, and variable subcellular distribution, are characteristic for the cytoplasmic tyrosine kinases. Tire nonreceptor tyrosine kinases are intracellular effector molecules that can associate with specific substrates during the process of signal transduction and activate these by tyrosine phosphorylation, to pass on the signal. Many of the functions of the nonreceptor tyrosine kinases are performed in the iimnediate vicinity of the cell membrane, whether a signal is received from an activated membrane receptor or a signal is passed on to a membrane-associated protein. 

In Fig. 8.14, the structures of some nonreceptor tyrosine kinases are shown schematically (review Taniguchi, 1995). Tire nonreceptor tyrosine kinases can be divided into different families based on sequence homology the Src family is the best characterized. In addition to the catalytic domain, the nonreceptor tyrosine kinases often have SH2 and SH3 domains responsible for specific association with substrate proteins. Nonreceptor tyrosine kinases that contain both SH2 and SH3 domains may be involved in signal transduction in larger protein complexes. 

Nonreceptor protein tyrosine kinases contain a catalytic domain, as well as various regulatory domains important for proper functioning of the enzyme. NRPTKs are found in the inner leaflet of the plasma membrane, cytosol, endosomal membranes and nucleus. These include the Src, Jak, Abl, Tec, Ack, Csk, Fak, Fes, Frk and Syk subfamilies (Fig. 24-3). Since a great deal is known about the structure and regulation of the Src family tyrosine kinase, we will use it to illustrate the principles in NRPTK signaling unique features in other subfamilies will be indicated... 

FIGURE 24-10 Schematic structures of nonreceptor protein tyrosine phosphatases (NRPTPs) and receptor protein tyrosine phosphatases (RPTPs). NRPTPs contain a catalytic domain and various regulatory domains. RPTPs are composed of an extracellular domain, a transmembrane domain and an intracellular domain with one or two catalytic domains. Like receptor protein tyrosine kinases, the structural features of the extracellular domains divide the RPTPs into different families. (With permission from reference [12]). 

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