Recombinant Human IGSF4B/SynCAM3 Protein, CF

IGSF4B (immunoglobulin superfamily member 4B), also called CADM3, TSLL1, Necl-1 and SynCAM-3, is a neural tissue-specific member of the nectin-like family of immunoglobulin superfamily (1, 2). It is a 48 - 50 kDa type I transmembrane (TM) glycoprotein that is concentrated at non-junctional contact sites of neuronal axons and glial processes (2, 3). In myelinated peripheral nerve fibers, IGSF4B is concentrated at nodes of Ranvier in contact sites of Schwann cells (2). The 398 amino acid (aa) human IGSF4B contains a 24 aa signal sequence, a 306 aa extracellular domain (ECD), a 21 aa transmembrane domain and a 47 aa cytoplasmic domain. The ECD contains an N-terminal V-type Ig-like domain that is responsible for Ca⁺⁺‑independent homophilic and heterophilic interactions with Nectin-1, Nectin-3 or Necl-2 (IGSF-4) in trans. It also contains two C2‑type Ig-like domains that are responsible for Ca⁺⁺-independent homophilic dimerization in cis that is thought to precede trans interaction (2, 4, 5). The cytoplasmic domain binds members of the MAGUK guanylate kinase subfamily, such as Dlg3, Pals2 and CASK (2). These activities are thought to play roles in adhesion and architecture at the synapse (2). We have also shown that IGSF4B promotes in vitro outgrowth of cortical neurons. Of two known splice variants, one shows an insertion of 34 aa near the mature N-terminus and probably represents a 60 kDa form. A smaller variant shows deletions of aa 185 - 231, and 281 - 398, which includes the first C2‑type Ig-like domain and the TM segment. The IGSF4B ECD is highly conserved, sharing 95 - 96% aa identity between human mouse, rat, canine and bovine sequences. The ECD of IGSF4A, B, C and D proteins share 35 - 50% aa identity.