ALK/LTK Subfamily

Anaplastic Lymphoma Kinase (ALK) and Leukocyte Tyrosine Kinase (LTK) receptors are grouped within the insulin receptor (IR) superfamily of receptor tyrosine kinases (RTKs). They share distinctive structural features, including highly conserved tyrosine kinase domains and unusual glycine-rich regions in their ligand-binding extracellular domains (ectodomains) that exhibit 55% amino acid identity between the receptors. Until recently, ALK and LTK were deorphanized when their physiological activating ligands, FAM150A (ALKAL1/AUGβ) and FAM150B (ALKAL2/AUGα), were identified. FAM150A functions as a high-affinity ligand of LTK. FAM150B functions as an activating ligand of both ALK and LTK. ALK and LTK have potential oncogenic properties.