Recombinant Human/Feline CXCL12/SDF-1 beta (aa 22-93)

CXCL12, also known as SCYB12, PBSF and SDF-1 beta, is an 8.3 kDa, heparin-binding member of the CXC (or alpha-) family of chemokines (1, 2). Feline CXCL12( beta) is synthesized as a 93 amino acid (aa) precursor that contains a 21 aa signal sequence and a 72 aa mature region (3). The mature molecule exhibits a typical three antiparallel beta-strand chemokine-like fold. There are no potential N-linked glycosylation sites. N-terminal aa’s 1-8 form a receptor binding site, while aa’s 1 and 2 (Lys-Pro) are involved in receptor activation (4). The C-terminus is likely associated with heparin binding (5). SDF-1 beta circulates and undergoes proteolytic processing. CD26 will remove the first two N-terminal amino acids, possibly creating a reduced-activity chemokine (5, 6). In addition to the beta-isoform, alternate splicing of the feline SDF-1 gene generates an alpha-isoform. The alpha isoform is identical to SDF-1 beta, but shorter by four aa’s at the C-terminus (3). Although alpha- and beta-isoforms show similar activity, SDF-1 alpha is differentially processed, and different cells secrete the two isoforms (5, 7). Mature feline SDF-1 beta is 96%, 97% and 100% aa identical to rat, mouse and human SDF-1 beta, respectively. Human (and by inference, feline) SDF-1 is active on mouse cells. SDF-1 alpha and beta are reported to be monomers at neutral pH and physiologic ionic strength (4). SDF-1 alpha is also reported to form dimers in the presence of heparansulfate (8). On the cell surface, this may well facilitate SDF-1 interaction with its two receptors, CXCR4 and syndecan-4 (9). Heparin sulfate is known to protect SDF-1 from proteolysis, and CXCR4 exists constitutively as a dimer (9-11). Among its many functions, CXCL12 is known to influence lymphopoiesis, regulate patterning and cell number of neural progenitors, and promote angiogenesis (12, 13). It also enhances the survival of myeloid progenitor cells.