Polymorphism among NILE-related glycoproteins from different types of neurons

We have used biosynthetic, degradative and immunochemical techniques to examine some of the structural features of the NILE (nerve growth factor inducible large external) glycoprotein. Biosynthetic experiments show that the NILE species present on PC12 cells has a core polypeptide with a molecular weight of 160,000 dalton. This polypeptide is initially glycosylated by immature, high mannose oligosaccharides to yield a precursor glycoprotein of 190,000 dalton. Oligosaccharide processing of this precursor in the Golgi apparatus yields the mature 230,000 dalton NILE glycoprotein. NILE-related glycoproteins from different neuronal cell types have molecular weights ranging from 215,000 to 230,000 dalton. Degradative experiments using neuraminidase to remove sialic acid residues and endoglycosidase F to remove all N-linked oligosaccharides indicate that the polymorphism of the NILE-related glycoproteins may be due to differences both at the polypeptide level and at the level of glycosylation. Although NILE glycoproteins and the neural cell adhesion molecule (N-CAM) both appear to be involved in neurite fasciculation, NILE and N-CAM components can be shown to be different from each other by several criteria. (1) The electrophoretic mobilities of NILE and N-CAM are different. NILE-related molecules from various sources migrate as single bands in the range of 215,000-230,000 dalton, while N-CAM from these same sources can exist as 3 separate components of 180,000, 140,000 and 120,000 dalton. (2) Rabbit antibody against NILE does not recognize N-CAM, and rabbit antibody against N-CAM does not recognize NILE. (3) N-CAM is present on some cell types that lack NILE. (4) The core polypeptides of NILE components have apparent molecular weights of about 160,000 dalton, while the N-CAM core polypeptide is about 120,000 dalton in size.