Kirrel2 (kin of irregular chiasm-1-like 2), also known as filtrin, NEPH3 (nephrin-like 3) or NLG1 (nephrin-like gene 1), is a 107kD type I transmembrane adhesion protein belonging to the immunoglobulin superfamily.1, 2 Kirrel2 is one of several proteins expressed both in pancreatic islet b cells and kidney glomerulus, and is also found in brain and lymph nodes.1-9 Mouse Kirrel2 cDNA encodes a 700 aa protein that contains a 16 aa signal sequence, a 491 aa extracellular domain with five C2-type Ig-like domains, a 21 aa transmembrane sequence and a 172 aa intracellular domain with a nephrin-like, conserved podocin binding site (mouse aa 589-598).4, 5 An extracellular RGD sequence allows for cell attachment.4 The extracellular domain of mouse Kirrel2 shares 96%, 86%, 85% and 85% amino acid (aa) identity with rat, human, equine and bovine Kirrel2, respectively. It shares 35-37% aa identity with other mouse Kirrel proteins. One mouse isoform that has been described is missing the transmembrane domain (aa 501-533), while another encodes only portions of Ig domains 1-4.5 Human Kirrel2 is downregulated in glomeruli of patients with proteinuria, suggesting an involvement in the maintenance of the glomerular filtration barrier.6 Autoantibodies to Kirrel2 have been identified in a subset of humans with type I diabetes, indicating its involvement with islet b cell function.7 In the brain, Kirrel2 is present in olfactory neurons, but only when they are active, homophilic adhesion of Kirrel2 is postulated to help correlate nerves identifying the same odorant.8 It is also a marker for mouse early postmitotic neural precursors in the ventricular zone of the developing mouse spinal cord.9 A DNA sequence encoding the extracellular domain of mouse Kirrel2 (Met 1-Asp 501, Accession NP_766486) was fused to a ten-histidine tag at the C-terminus. The protein was expressed in a mouse myeloma cell line, NS0. Calculated molecular mass of 52.7kD. As a result of glycosylation, the recombinant protein migrates as an ~ 66kD protein in SDS-PAGE under reducing conditions. Activity: Measured by the ability of the immobilized protein to support the adhesion of MS-1 cells (mouse pancreatic islet endothelial cell line). Storage and Stability: Lyophilized powder may be stored at 4C for short-term only. Reconstitute to nominal volume by adding sterile PBS and store at -20C. Reconstituted product is stable for 12 months at -20C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. Further dilutions can be made in assay buffer.
