Recombinant Human FLRT1 Protein, CF

FLRT1 is one of three FLRT (fibronectin, leucine rich repeat, transmembrane) glycoproteins expressed in distinct areas of the developing brain and other tissues (1, 2). The 90 kDa type I transmembrane (TM) human FLRT1 is synthesized as a 646 amino acid (aa) precursor with a 20 aa signal sequence, a 504 aa extracellular domain (ECD), a 21 aa TM segment and a 101 aa cytoplasmic region. The ECD contains 10 N-terminal leucine-rich repeats flanked by cysteine-rich areas, and a juxtamembrane fibronectin type III domain (1). The human FLRT1 ECD shares 97% aa sequence identity with mouse, rat, and canine, and 95% with bovine FLRT1 ECD. Human FLRT2 and FLRT3 ECDs share 47% and 61% aa identity, respectively, with FLRT1. The fibronectin domain of all three FLRTs can bind FGF receptors (2). This binding is thought to regulate FGF signaling during development (2, 3). The LRR domains are responsible for both the localization of FLRTs in areas of cell contact and homotypic cell-cell association (4). This may be through direct interactions with other FLRT molecules or, as has been shown for FLRT3, by regulating internalization of adhesion molecules such as cadherins (4, 5). Both during development and in adulthood, FLRT1 mRNA is predominantly expressed in brain and kidney (1). FLRT1 is expressed at brain compartmental boundaries in mouse embryos (2). Its expression is distinct from that of FLRT2 and FLRT3 (2).