STRUCTURAL AND ELECTRON-MICROSCOPIC ANALYSIS OF NEUROCAN AND RECOMBINANT NEUROCAN FRAGMENTS

Neurocan, a nervous tissue-specific chondroitin sulfate proteoglycan o f the aggrecan family which has been shown to interact with neural cel l adhesion molecules and tenascin, could be visualized by rotary shado wing electron microscopy as two globular domains interconnected by an extended flexible filament of 60-90 nm, Several recombinant neurocan f ragments generated in the human embryonic kidney cell line 293 represe nt as observed by electron microscopy the expected parts of this struc ture, which indicates a correct folding of these molecules. Biological activity of the recombinant N-terminal globular domain could be demon strated by its coelution with hyaluronan in gel permeation chromatogra phy. In addition, the modification of the recombinant fragments with c ertain carbohydrate structures was analyzed. High mannose oligosacchar ides could be mapped to the N-terminal globular domain of the brain-de rived molecule. Only recombinant fragments containing parts of the cen tral region of the molecule were modified with chondroitin sulfate cha ins and with the HNK-1 epitope, and could be considerably altered in t heir migratory behavior on SDS-polyacrylamide gel electrophoresis by n euraminidase treatment, These findings and the electron microscopic sh ape indicate a mucin-like character for the central neurocan region.