Nogo-B belongs to the reticulon family of proteins, characterized by having the reticulon homology domains (RHDs) at the C-termini. The best characterized member of the reticulon family is RTN4, which has three isoforms: Nogo-A, the largest among the three isoforms with full length human protein consisting of 1192 aa and a calculated molecular weight of 135 kD; Nogo-B, an intermediate form with 373 aa and a molecular weight of ~37 kD; and a shorter form, Nogo-C, with 199 aa, a molecular weight of ~25 kD, and a very small N-terminal region. Nogo-B is a spliced variant of Nogo-A, while Nogo-C uses an alternative promoter and unique exon to encode its short amino terminus. Nogo-A and Nogo-B share an identical N-terminal region (aa 1-185), while this region is absent in Nogo-C.