Myelin glycosylation

Glycosylation of myelin protein elements in the peripheral and central nervous system (V5) may have fundamental implications for nerve conduction and central nervous system functions. 

V6. Vlassara, H., Brownlee, M., and Cerami, A., Excessive nonenzymatic glycosylation of peripheral and central nervous system myelin components in diabetic rats. Diabetes 32, 670-674 (1983). 

Less information is available about the possible recognition site of the glycosyltransferases which add sugar residues to serine or threonine in proteins. In some cases there appears to be a correlation between the occurrence of proline residues and glycosylation. In bovine myelin Al protein, the carbohydrate chain occurs in the sequence -Pro-Arg-Thr-... 

Fig. 5. Glycoproteins. Known reactions in the synthesis of submaxillary gland glycoproteins. The specificity of AZ-acetylgalactosaminyl transferase responsible for synthesis of I was studied using basic myelin protein [an unusual substrate which is not normally glycosylated partial structure Val(94) Thr-Pro-Arg-Thr-Pro-Pro-Pro(IOI)-]. Glyeosylation is specific for Thr 98 (Thr 95 is not glycosylated) a proline-rich environment appears to be necessary around the glycosylated hydroxyamino acid residue.

Surfactant convertase, a diisopropylfluorophos-phate (DFP)-binding and DFP inhibitable carboxyl-esterase (Gross et al. 1997) of 70 kDa (reduced), is required for conversion of heavy density (tubular myelin) to fight density (small vesicle) subtypes of surfactant. Carboxylesterase ES-2 mRNA was localised to type II pneumocytes and alveolar macrophages but not to Clara cells (Clark et al. 1997). Lamellar bodies contain both glycosylated (70 kDa)... 

Thirty years ago, Quarles et al. described a heavily glycosylated protein from myelin preparatimis [4], which they called myelin-associated glycoprotein [5], abbreviated MAG. Over the following 10 years, Quarles and his coworkers characterized this protein before it drew further attention from other laboratories, induced by the seminal observatiOTi that MAG is developmentally regulated in myelinating cells [6] and is possibly involved in multiple sclerosis [7], two publications, which together have been cited over 500 times. 

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