CD117 is a cell surface receptor belonging to the Tyrosine kinase receptor family. The molecule is recognized as a receptor for the stem cell factor (mast cell factor), and is expressed on hematopoeitic stem cells, acute myeloid leukemic cells, tissue mast cells, and melanocytes. Binding of the ligand on to the receptor causes autophosphorylation of the receptor, and leads to its association with substrates such as phosphatidylinsoitol 3-kinase.

The protein is central for the development of several lineages of stem cells, and plays a major role in functions such as hematopoeisis, melanogenesis, and gametogenesis. It induces mast cell differentiation, proliferation, migration, survival, their adhesion to extracellular proteins, and secretion of mast cell mediators, like TNF-alpha, esterase, protease, and others. CD117 is implicated in diseases such as familial gastrointestinal stromal tumors, leukemia, and systemic mast cell disease. Genetic tests are now available to detect mutations in the Kit gene, and assess susceptibility and treatment regimen for GI tumors.

The gene coding for CD117 is an 89 Kb long stretch of DNA, located on chromosome 4. The gene has 21 exons, alternative splicing of which lead to generation of two protein product-KitA and Kit.

The Kit protein is 976 amino acids long. The extracellular region of the protein has 497 amino acids in it, and contains five immunoglobulin-like domains. The transmembrane domain is highly hydrophobic and is made of 23 amino acid residues. The tyrosine kinase domain is seen in the intercellular region of the protein.