Catalytic domain of the Protein Tyrosine Kinases, Anaplastic Lymphoma Kinase and Leukocyte Tyrosine Kinase
PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyr residues in protein substrates. ALK and LTK are orphan receptor PTKs (RTKs) whose ligands are not yet well-defined. 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. 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. The ALK/LTK subfamily is part of a larger superfamily that includes the catalytic domains of other kinases such as serine/threonine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
Jiyao W et al.(2023). "The conserved domain database in 2023.",