Caspr is a contactin-associated protein. Caspr is part of the neurexin family of proteins. It lies in the paranodal section of the myelin sheath, between the Nodes of Ranvier containing Na+ channels, and K+ channels in the juxtaparanodal region. Its role is for myelin sheath attachment along with contactin (laterally) in a cis-complex. In staining, it shows up as green with immunohistochemical steps, and along with VNa (red) shows a red/green contrast to stain for defects in myelin sheath, and size of Nodes of Ranvier. In Western Blotting it has a predicted Molecular Weight around 156kDa but due to a number of potential glycosylation sites, is 180kDa.