cd05036: PTKc_ALK_LTK (this model, PSSM-Id:133168 is obsolete and has been replaced by 270632)
Catalytic domain of the Protein Tyrosine Kinases, Anaplastic Lymphoma Kinase and Leukocyte Tyrosine Kinase
Protein Tyrosine Kinase (PTK) family; Anaplastic Lymphoma Kinase (ALK) and Leukocyte Tyrosine (tyr) Kinase (LTK); catalytic (c) domain. The PTKc family is part of a larger superfamily that includes the catalytic domains of other kinases such as protein serine/threonine kinases, RIO kinases, and phosphoinositide 3-kinase (PI3K). PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyr residues in protein substrates. ALK and LTK are orphan receptor tyr kinases (RTKs) whose ligands are not yet well-defined. RTKs contain an extracellular ligand-binding domain, a transmembrane region, and an intracellular tyr kinase domain. They are usually activated through ligand binding, which causes dimerization and autophosphorylation of the intracellular tyr kinase catalytic domain. ALK appears to play an important role in mammalian neural development as well as visceral muscle differentiation in Drosophila. ALK is aberrantly expressed as fusion proteins, due to chromosomal translocations, in about 60% of anaplastic large cell lymphomas (ALCLs). ALK fusion proteins are also found in rare cases of diffuse large B cell lymphomas (DLBCLs). LTK is mainly expressed in B lymphocytes and neuronal tissues. It is important in cell proliferation and survival. Transgenic mice expressing TLK display retarded growth and high mortality rate. In addition, a polymorphism in mouse and human LTK is implicated in the pathogenesis of systemic lupus erythematosus.