N‐Cadherin Is a Major Glycoprotein Component of Isolated Rat Forebrain Postsynaptic Densities

Abstract

Abstract: We have previously described a monoclonal antibody, PAC 1, that recognises two postsynaptic density (PSD)‐enriched glycoproteins (pgps) of apparent M r 130,000 (pgp130) and 117,000 (pgp117). Immunodevelopment of western blots of rat forebrain homogenate, synaptic membrane (SM), and PSD samples with PAC 1 and an N‐cadherin antiserum shows that pgp130 and N‐cadherin are of identical apparent M r and show identical patterns of enrichment in these fractions. The apparent molecular masses of pgp130 and N‐cadherin are both lowered by 11 kDa following removal of N ‐linked carbohydrate with endoglycosidase‐F containing N ‐glycopeptidase. The two molecules show an identical pattern of migration when separated by two‐dimensional electrophoresis. A single 130‐kDa band immunoprecipitated from solubilised PSD preparations by the N‐cadherin antiserum is recognised by PAC 1 on western blots. We conclude that pgp130 is N‐cadherin. Development of western blots of two‐dimensional gel separations of SM and PSD glycoproteins shows that N‐cadherin is a major glycoprotein component of PSDs. The immunoprecipitation experiments show that the M r of N‐cadherin is greater than that of the major pgp, PSD gp116. The PAC 1 antibody recognises two concanavalin A‐binding glycoproteins with apparent molecular masses of 136 and 127 kDa in liver samples. The 136‐kDa band is also recognised by the N‐cadherin antiserum. These observations, together with data showing that the PAC 1 epitope is intracellular, suggest that PAC 1 is a pan‐cadherin antibody and recognises an epitope on the conserved cadherin intracellular carboxyl‐terminal domain.