Fig. 1.

The Nogo receptor family. The Nogo receptors NgR1, NgR2, and NgR3 comprise a small subfamily of leucine-rich repeat (LRR) proteins. The three receptors share an identical overall domain organization composed of a cluster of 8.5 canonical LRRs flanked N-terminally by a LRRNT capping domain and C-terminally by a LRRCT capping domain. The LRRNT-LRR-LRRCT domains are connected via a stalk region to a glycosylphosphatidyl inositol (GPI) anchor. We identified s-NgR2, a soluble form of NgR2 that is the product of alternative splicing of exon III of the NgR2 gene. The first 171 amino acid residues of s-NgR2 are identical with full-length NgR2 and are followed by 22 amino acids unique to s-NgR2. NgR1 is a 65-kDa glycoprotein that supports binding of Nogo, MAG, and OMgp. NgR2 is a 65-kDa glycoprotein and supports binding of MAG but not Nogo or OMgp. Thus far no binding partners for NgR3 have been identified.