The leucine-rich (LRR) repeat is a 20-30 amino acid motif that forms a hydrophobic ?/∫ horseshoe fold, allowing it to accommodate several leucine residues within a tightly packed core. All LRR repeats contain a variable segment and a highly conserved segment, the latter of which accounts for 11 or 12 residues of the entire LRR motif. ISLR2 (immunoglobulin superfamily containing leucine-rich repeat 2), also known as LINX (leucine-rich repeat domain and immunoglobulin domain-containing axon extension protein), is a 745 amino acid single-pass membrane protein that contains five LRR repeats, one Ig-like (immunoglobulin-like) domain, a LRRCT domain and one LRRNT domain. ISLR2 exists as a homomultimer and is essential for axon extension during neural development. The gene encoding ISLR2 maps to human chromosome 15q24.1.