Purification and characterization of the D2 cell adhesion protein: analysis of the postnatally regulated polymorphic forms and their cellular distribution.

The developmentally regulated, D2 cell adhesion protein has been purified from 10-12 day old rat synaptosomes by sequential hydroxyapatite chromatography, wheat germ lectin affinity chromatography and gel filtration. The purified protein was found to be composed of two polypeptide components of 200 and 140 kd molecular weight which comprised 0.5-1.0% of total synaptosomal membrane protein. Lysine-Sepharose affinity chromatography could further separate the purified protein into sialic acid-rich and sialic acid-poor forms. Immunoblot analysis of whole brain homogenates and synaptosomes with an antiserum raised against the purified protein (anti-D2) revealed the presence of three immunologically related polypeptides of 200, 140, and 115 kd molecular weight. These polypeptides, which appeared as a diffuse zone (greater than 200 kd) in fetal material, were found to developmentally regulate by altering their relative expression. This was particularly marked in the 200 kd component. Furthermore, the 200 kd polypeptide appeared to be neuron-specific as both the 140 and 115 kd components were common to synaptosomes and primary cultures of astrocytes.