Neuroplastin (NPTN; also stromal cell-derived receptor 1 and Np55) is a 52 - 57 kDa member of the Ig-superfamily. Neuroplastin is widely expressed and likely serves as a cell adhesion molecule in multiple tissues. Human Neuroplastin is 282 amino acids (aa) in length. It is a type I transmembrane glycoprotein that contains two Ig-like domains (aa 32 - 119 and 122 - 213) and a 38 aa cytoplasmic region (aa 245 - 282).
There is a brain-enriched 65 kDa form of Neuroplastin 65 (Np65) that negatively regulates LTP in the hippocampus. Neuroplastin 65 contains an N-terminal 116 aa Ig-like domain-containing insert after Asn30 and interacts homotypically. Notably, human and rodent Np65 expression patterns are different in brain, with rodent Np65 not predominating in cerebellum. Over aa 29 - 336, human Np65 is 95% aa identical to mouse Np65.