Biochemical Demonstration of the Myelin‐Associated Glycoprotein in the Peripheral Nervous System

Abstract

Recent immunocytochemical studies indicated that the myelin-associated glycoprotein (MAG) is localized in the periaxonal region of central nervous system (CNS) and peripheral nervous system (PNS) myelin sheaths but previous biochemical studies had not demonstrated the presence of MAG in peripheral nerve. The glycoproteins in rat sciatic nerves were heavily labeled by injection of [3H]fucose in order to re-examine whether MAG could be detected chemically in peripheral nerve. Myelin and a myelin-related fraction, W1, were isolated from the nerves. Labeled glycoproteins in the PNS fractions were extracted by the lithium diiodosalicylate (LIS)-phenol procedure, and the extracts were treated with antiserum prepared to CNS MAG in a double antibody precipitation. This resulted in the immune precipitation of a single [3H]fucose-labeled glycoprotein with electrophoretic mobility very similar to that of [14C]fucose-labeled MAG from rat brain. A sensitive peptide mapping procedure involving iodination with Bolton-Hunter reagent and autoradiography was used to compare the peptide maps generated by limited proteolysis from this PNS component and CNS MAG. The peptide maps produced by three distinct proteases were virtually identical for the two glycoproteins, showing that the PNS glycoprotein is MAG. The MAG in the PNS myelin and W1 fractions was also demonstrated by Coomassie blue and periodic acid-Schiff staining of gels on which the whole LIS-phenol extracts were electrophoresed, and densitometric scanning of the gels indicated that both fractions contained substantially less MAG than purified rat brain myelin. The presence of MAG in the periaxonal region of both peripheral and central myelin sheaths is consistent with a similar involvement of this glycoprotein in axon-sheath cell interactions in the PNS and CNS.

Axonal modulation of myelin gene expression in the peripheral nerve

“…P, is strongly homologous to lipid binding proteins and is thought to have an active role in fatty acid elongation or transport during the process of myelination (Narayanan et al, 1988). MAG is found mostly at the periaxonal region, and its localization supports a role for this protein in the initial formation of Schwann cell-axon contact (Figlewicz et al, 1981;Trapp and Quarles, 1982;Quark s , 1983). Cloning of the myelin specific genes has revealed single copy genes per haploid genome (reviewed by Lemke, 1986Lemke, , 1988Sutcliffe, 1987).…”

Quantitative and Integrative Proteome Analysis of Peripheral Nerve Myelin Identifies Novel Myelin Proteins and Candidate Neuropathy Loci

“…Sixty-three membranespanning proteins were identified (Table 1), including established myelin proteins such as P0 (D'Urso et al, 1990;Filbin et al, 1990;Giese et al, 1992); MAG (Figlewicz et al, 1981); sarcoglycan-␦ (Cai et al, 2007), nectin-like protein-4 (NECL4) (Spiegel et al, 2007); and the tetraspan-transmembrane proteins proteolipid protein (PLP/DM20), plasmolipin (PLLP), CD81, and CD9 (Garbern et al, 1997;Bosse et al, 2003;Ishibashi et al, 2004 Figure 2. Two-dimensional myelin proteome maps.…”

“…It became evident that PNS myelin contains more proteins than assumed upon the immunoblot-based demonstration that a known CNS myelin component, the Ig-CAM myelin-associated glycoprotein (MAG), is also present in PNS myelin (Figlewicz et al, 1981). Later, additional myelin proteins were identified by using myelin-directed antibodies or amino acid sequence information gained from purified myelin, such as the tetraspan peripheral myelin protein of 22 kDa (PMP22) (Welcher et al, 1992) and the scaffolding protein periaxin (PRX) (Gillespie et al, 1994).…”

Methods for the Identification and Characterization of Glycoproteins in Central and Peripheral Myelin

“…Its presence was only demonstrated by immune precipitation. (The radioactive profile in this figure was reproduced from Figlewicz et al, 1981. with the permission of Raven Press.…”