Recombinant Human SCF/c-kit Ligand Biotinylated Protein, CF

Mature stem cell factor consists of a 189 amino acid (aa) extracellular domain (ECD), a 23 aa transmembrane domain, and a 36 aa cytoplasmic tail (10). The ECD shows both N linked and O-linked glycosylation (11). SCF protein exists in two forms, a membrane-bound form and a proteolytically processed soluble form that lacks the transmembrane domain and cytoplasmic tail. The soluble form is created by proteolytic cleavage at two alternate sites in the extracellular juxtamembrane region releasing a 25 kDa soluble SCF protein which is comparable to the only form produced by Steel-dickie mutant mice (12, 13). There is also an alternately spliced isoform of human SCF that lacks 28 amino acids that encompasses the primary proteolytic recognition site (14). This form cannot be cleaved and is only membrane bound. SCF binds to C-kit (CD117). C-kit is expressed on many different cell types including HSCs, mast cells, germ cells, and melanocytes. Binding of SCF to C-kit induces receptor dimerization and autophosphorylation of tyrosine residues in the cytoplasmic domain (15). Tyrosine phosphorylation initiates multiple signaling pathways including RAS, PI3 kinase, Src, and JAK/STAT. Stem cell factor is highly conserved among mammals. Human SCF protein shares 79% 87% aa sequence identity with dog, cat, mouse, and rat SCF. Rat SCF is active on mouse and human cells, but human SCF is only weakly active on mouse cells (10).