Transmembrane domains protein tyrosine kinases

Receptor protein tyrosine kinases consist of an extracellular domain, a single transmembrane domain and a cytoplasmic domain 419... 

FIGURE 24-6 Schematic structures of receptor protein tyrosine kinase (RPTK) families. RPTKs can be divided into different families according to the structural features in the extracellular domain. Following the extracellular domain are the transmembrane and intracellular domains the latter contains the catalytic domain. (From reference [5], with permission of Nature. Nature 2001.)... 

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]). 

Receptor Single transmembrane a helix intrinsic protein tyrosine kinase activity in cytosolic domain... 

Receptors that are a transmembrane protein with a ligand-binding site on the extracellular side and a catalytic domain on the cytosolic side. In the insulin receptor, for example, the catalyst is a protein tyrosine kinase, which is stimulated by insulin binding to the extracellular domain of the receptor. 

The cytoplasmic domains of all of these receptors have an intrinsic protein tyrosine kinase activity, and all the receptors have hydrophobic transmembrane sequences. Their extracellular regions are more variable in stmcture. Depending on the receptor, they may contain a range of domains, including (1) immrmoglobulin domains, (2) cysteine-rich motifs, (3) fibronectin type III repeats, and (4) EGF motifs. These can be present singly or in different combinations. Growth factor receptors are therefore examples of mosaic proteins. 

Besides cytoplasmic protein kinases, membrane receptors can exert protein kinase activity. These so-called receptor tyrosine kinases (RTK) contain a ligandbinding extracellular domain, a transmembrane motif, and an intracellular catalytic domain with specificity for tyrosine residues. Upon ligand binding and subsequent receptor oligomerization, the tyrosine residues of the intracellular domain become phosphory-lated by the intrinsic tyrosine kinase activity of the receptor [3, 4]. The phosphotyrosine residues ftmction as docking sites for other proteins that will transmit the signal received by the RTK. 

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