Characterization of protein-linked glycoconjugates produced by identified neurons of Aplysia californica.

The biosynthetic capabilities of individual neurons of the abdominal ganglion of the marine mollusc Aplysia californica have been analyzed after intrasomatic injection of 3H-monosaccharides. Glycopeptides prepared from the metabolically labeled cells were fractionated using serial lectin affinity and gel filtration chromatography. The fractionation procedure yielded eight populations of glycopeptides, and comparison of two different neurons (R2 and R14) showed that the quantity of the individual species produced is cell-dependent. Structural analysis indicated that the glycoconjugates produced by the Aplysia neuron constitute both O- and N-linked structures as well as an unusual class of oligosaccharide whose linkage to protein is unknown. The O-linked units are small and consist only of N-acetylglucosamine or N-acetylgalactosamine attached to protein. High-mannose-type asparagine-linked units are produced by the neurons, and some of these appear to be processed to biantennary complex-type units that bind to lentil lectin-agarose. Overall, although the Aplysia neurons produce oligosaccharides of a nature similar to that produced by higher eucaryotes, the N- and O-linked structures produced by the neurons do not achieve the complexity of the comparable structures produced by mammalian cells. The results provide a basis for further studies aimed at understanding the role of glycoconjugates in the development of the nervous system.