Structural and functional studies on N-CAM neural cell adhesion molecules.
The neural cell adhesion molecules N-CAM are to date the best characterized adhesion molecules of the nervous system. They have a high content of sialic acid residues which are present in the form of unusual sialic acid polymers. During development, a 3 fold decrease in the sialic acid content is observed. These changes in the degree of sialylation profoundly affect the binding properties of the molecules. A subpopulation of mouse brain N-CAM bears a carbohydrate determinant shared with other brain cell surface proteins and with the HNK-1 antigen of natural killer cells. Not only the carbohydrate side chains but also the protein moieties of the N-CAMs are heterogeneous. Three polypeptides of 180 K, 140 K and 120 K have been characterized in mouse brain. The 180 K and 140 K chains span the membrane. They differ mainly by the length of their cytoplasmic extensions. These intracellular domains are unusually long and contain phosphorylated serine residues. The 120 K chain exists in two forms, one membrane-bound and one soluble. Earlier studies had shown the presence of N-CAM on neurones and astrocytes of the mouse central nervous system, whereas cultured astrocytes had been reported to be N-CAM-negative. Recent results show that N-CAM is also expressed on astrocytes in culture. To study expression and heterogeneity of N-CAM polypeptides at the mRNA and gene level, cDNA clones for mouse N-CAM have been isolated. They reveal multiple mRNA species in mouse brain. By contrast, the corresponding sequences seem to be present only a few times, perhaps only once, in the mouse genome.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D000954:Antigens, Surface / Q000235:genetics / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules; D055598:Chemical Phenomena; D002621:Chemistry; D003001:Cloning, Molecular; D004247:DNA / Q000378:metabolism; D006023:Glycoproteins / Q000502:physiology*; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D009447:Neuroblastoma; D012333:RNA, Messenger / Q000378:metabolism; D013329:Structure-Activity Relationship
D000954:Antigens, Surface; D015815:Cell Adhesion Molecules; D006023:Glycoproteins; D008565:Membrane Proteins; D012333:RNA, Messenger; D004247:DNA