Recombinant Human CXCL16 Protein

CXC chemokine ligand 16 (CXCL16) is a type I membrane protein containing a non-ELR motif-containing CXC chemokine domain in its extracellular region. Together with Fractalkine (CX3CL1), CXCL16 constitute the only two transmembrane chemokines within the superfamily. The gene for human CXCL16 predicts a 273 amino acid (aa) residue precursor protein with a putative signal peptide, a CXC chemokine domain, a mucin-like spacer region, a transmembrane domain and a cytoplasmic domain with a potential tyrosine phosphorylation and SH2 protein-binding site. Mouse and human CXCL16 share 70% aa sequence similarity within their chemokine domains and 49% overall aa sequence identity. By northern blot analysis, CXCL16 expression is detected in various human organs except for brain, bone marrow, skeletal muscle or colon. By flow cytometry, CXCL16 has been detected on the surface CD19⁺ B cells, CD14⁺ monocytes/macrophages, and CD11c⁺ splenic and lymph node dendritic cells. Functional CXCL16 can be shed from the cell surface as an approximately 35 kDa soluble protein. The functional receptor for CXCL16 has been identified as CXCR6 (also known as Bonzo, STRL33 or TYMSTR), a receptor previously shown to be a co-receptor for HIV entry. CXCL16 has also been independently cloned and named SRPSOX (scavenger receptor that binds phosphatidylserine and oxidized lipoprotein). It was shown to be a specific receptor for OxLDL but not LDL or acetyl-LDL.