Human SREC-II/SCARF2 Alexa Fluor® 594-conjugated Antibody

The scavenger receptor (SR) family comprises a group of functionally defined membrane receptors that share a common ability to bind and internalize modified forms of low density lipoproteins (LDL) such as acetylated LDL (AcLDL) and oxidized LDL(OxLDL) (1‑3). Family members are classified alphabetically. In general, they play important roles in lipid metabolism, in host defence and in the regulation of acquired immunity (2, 4). Scavenger receptor expressed by endothelial cells-I (SREC-I) and SREC-II are two proteins that belong to the F type scavenger receptor group (SR-F1 and SR-F2). Unlike SREC-I, SREC-II is somewhat unique in that it doesn’t show expected binding to modified LDL (5). The full length cDNA for human SREC-II encodes an 870 amino acid (aa) type I transmembrane protein which contains a 43 aa signal peptide, a 398 aa extracellular region, a 21 aa transmembrane segment, and a 408 aa cytoplasmic domain (5, 6). Depending upon the reference, the extracellular region contains 7‑10 EGF-like repeats, with a cytoplasmic domain that is rich in serine and proline in its N-terminal half and glycine in its C-terminal segment (5, 6). There is at least one alternate splice variant that shows a 5 aa deletion in the juxtamembrane region of the cytoplasmic domain (6, 7). The deletion does not change the reading frame as the distal 390 amino acids are identical in the two isoforms. The Genbank suggests another variant is possible involving amino acids 750‑768 of the precursor. Again, this doesn’t seem to change the reading frame as amino acids downstream of this are unchanged (6, 8). SREC-II is expressed by endothelial cells and vascular smooth muscle cells (5, 9). In the extracellular region human SREC-II is 95% aa identical to mouse SREC-II. The extracellular regions of human SREC-II and SREC-I are 53% aa identical. Notably, more than serving as a scavenger receptor, SREC-II would seem to form heterophilic interactions with SREC-I during cell-to-cell aggregation (5).