Myelin-associated glycoproteins

Rodriguez-Pena A, Ibarrola N, Iniguez MA, Munoz A, Bernal J 1993 Neonatal hypothyroidism affects the timely expression of myelin-associated glycoprotein in the rat brain. J Clin Invest 91 812-818... 

Georgiou, J., Tropak, M. P. and Roder, J. C. Myelin-associated glycoprotein gene. In R. A. Lazzarini (ed.), Myelin biology and disorders. San Diego, CA Elsevier Academic Press, 2004, 421-467. 

FIGURE 7-1 The immunoglobulin (Ig) gene family of molecules. Several varieties of Ig domain-containing molecules are contained within the Ig gene superfamily. Most are type I membrane proteins some have only Ig domains or other moieties that may convey function (see text). V, variable Ig domain C, constant Ig domain MAG, myelin-associated glycoprotein NCAM, neural cell adhesion molecule GPI, glycosylphosphatidyl-inositol EC, extracellular domain FN, fibronectin. 

Kelm, S., Pelz, A., Schauer, R. etal. Sialoadhesin, myelin-associated glycoprotein and CD22 define a new family of sialic acid-dependent adhesion molecules of the immunoglobulin superfamily. Curr. Biol. 4 965-972,1994. 

Filbin, M. T. Myelin-associated glycoprotein a role in myelination and in the inhibition of axonal regeneration Curr. Opin. Neurobiol. 5 588-595,1995. 

The syndrome of IgMk paraproteinemia and sensory ataxia is usually encountered in elderly men. Nerve biopsy in these patients shows focal abnormalities in compaction of PNS myelin lamellae, and their IgM paraprotein recognizes epitopes of myelin-associated glycoprotein (MAG) and sulfate-3-glucuronyl paragloboside [24,42]. 

Peripheral neuropathy occurs in about 16% of patients with MGUS, being particularly common in those with an IgM monoclonal gammopathy [128], The IgM fraction of such patients includes antibodies to myelin-associated glycoprotein (MAG antibodies) that bind to determinants in peripheral nerve myelin, and, as shown by animal models, the antibodies mediate the myelin injury and secondary nerve damage [129]. The patients usually have a distal symmetric neuropathy, usually with predominant sensory affection, and the neurological symptoms frequently precede the detection of gammopathy [130]. 

Myelin is modified plasma membrane. Myelin of the PNS resembles that of the CNS with respect to lipid composition. There is an enrichment in such specialized lipids as cerebroside and ethanolamine plasmalogen, and the high content of cholesterol plays an important role in control of membrane fluidity. The protein composition of PNS myelin is, however, distinct from that of CNS myelin. A single protein, P0, accounts for half of all protein of PNS myelin. Of the other proteins present, most are expressed in the CNS as well as the PNS but in quantitatively different amounts. Prominent among these proteins are myelin basic proteins and myelin-associated glycoprotein. 

Fig. 11. Schematic representation of the myelin-associated glycoproteins and their receptors and co-receptors involved in inhibition of neurite outgrowth. The Nogo receptor (NgR) and associated co-receptors are expressed on neurons while its ligands, NogoA, OMgp, and MAG, are expressed on the oligodendrocyte cell surface.

Tang, S., Shen, Y. J., DeBellard, M. E., Mukhopadhyay, G., Salzer,J. L., Crocker, P. R., and Filbin, M. T. (1997). Myelin-associated glycoprotein interacts vdth neurons via a sialic acid binding site at ARG118 and a distinct neurite inhibition site./ Cell Biol. 138, 1355-1366. 

Owens GC, Bunge RP (1989) Evidence for an early role for myelin-associated glycoprotein in the process of myeUnation. GUa 2 119-128... 

Vyas A, Patel H, Eromholt S, Heffer-Lauc M, Vyas K, Dang J, Schachner M, Schnaar R. Gangliosides are functional nerve cell ligands for myelin-associated glycoprotein (MAG), an inhibitor of nerve regeneration. Proc. Natl. Acad. Sci. U.S.A. 2002 99 8412-8417. 

Vyas AA, Blixt O, Paulson JC, Schnaar RL. Potent glycan inhibitors of myelin-associated glycoprotein enhance axon outgrowth in vitro. J. Biol. Chem. 2005 280 16305-16310. Iwabuchi K, Zhang Y, Handa K, Withers DA, Sinay P, Hako-mori S. Reconstitution of membranes simulating glycosignaling domain and their susceptibility to lyso-GM3. J. Biol. Chem. 2000 275 15174-15181. 

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