Recombinant Human ROBO2 Fc Chimera Protein, CF

Human ROBO2 is a 175 kDa member of the ROBO family of guidance molecules (1-3). The term ROBO derives from round-about, a description of the circuitous pathway axons take in the absence of a functional ROBO gene (3, 4). Human ROBO2 is a type I transmembrane (TM) glycoptotein that is synthesized as a 1378 amino acid (aa) precursor. It contains a 21 aa signal sequence, an 838 aa extracellular domain (ECD), a 21 aa transmembrane segment, and a 498 aa cytoplasmic region (5, 6). The ECD contains five C2-type Ig-like domains (aa 31-504) and three fibronectin (FN) type III domains (aa 522-826). The cytoplasmic region contains multiple 15-20 aa long CC (conserved cytoplasmic) motifs (C0-C2) that are found in ROBO-1 (7, 8). Human ROBO2 has at least two potential isoforms. One isoform shows a cytoplasmic truncation of the C-terminus (aa 1186-1378) (9). A second isoform is a 570 aa soluble form that shows a deletion of the first two and one-half C2-type Ig-like domains (aa 22 - 285) and terminates after the third fibronectin domain with a unique 20 aa sequence (10). Based on mouse and rat ROBO2 GenBank sequences, considerably more alternate splice forms may occur. Human ROBO2 ECD is 98% aa identical to the ECD in mouse and canine ROBO2. ROBO2 would appear to play a number of roles in cell adhesion. In the neural tube, it is the receptor for a chemorepulsant. Axons that cross the midline are directed, presumably by ROBO2/SLIT chemorepulsion, to lateral positions in the contralateral spinal cord (6, 11, 12). In addition, ROBO2 is both permissive for neurite outgrowth (via ROBO1‑ROBO2 interaction) and inhibitory for neurite outgrowth (via ROBO2-SLIT interaction) (13, 14).