Chemokines

The SDF‐1 proteins are stromal‐derived CXC chemokines that signal primarily through the CXCR4 receptor. SDF‐1 proteins exert chemotactic activity over a broad range of immune system cell types and may also be involved in other processes including metastasis of certain cancers, inflammation, and angiogenesis. Additionally, SDF‐1 can suppress HIV entry into cells expressing the CXCR4 receptor. Five isomers of SDF‐1 have been found with SDF‐1α being the predominant form, expressing in a wide range of cell types. The SDF‐1γ isoform is distinctive in that it contains a highly basic C‐terminal region, which presumably is the reason for its high binding affinity to gylcosaminoglycans (GAG) and heparin sulfate (HS). Consequently, most of SDF‐1γ exists in a cell‐ and membrane‐bound form, which confers greater stability compared to other isoforms via increased resistance to proteolytic degradation. SDF‐1γ binds with reduced affinity to the CXCR4 receptor when compared to the α and β isoforms, but because of its increased stability can, over time, exert equal or greater activity when compared to other SDF‐1 isoforms. SDF‐1γ expression has been found primarily in the heart (human and mouse) and in the brain and central nervous system (rat). Recombinant Human SDF‐1γ (CXCL12) is an 11.6 kDa protein containing 98 amino acid residues.