Myelin based protein

Tsekenis, G., et al., 2008. Label-less immunosensor assay for myelin basic protein based upon an AC impedance protocol. Anal. Chem. 80 (6), 2058-2062. Available at http //pubs.acs. org/doi/abs/10.1021/ac702070e. 

Myelin in situ has a water content of about 40%. The dry mass of both CNS and PNS myelin is characterized by a high proportion of lipid (70-85%) and, consequently, a low proportion of protein (15-30%). By comparison, most biological membranes have a higher ratio of proteins to lipids. The currently accepted view of membrane structure is that of a lipid bilayer with integral membrane proteins embedded in the bilayer and other extrinsic proteins attached to one surface or the other by weaker linkages. Proteins and lipids are asymmetrically distributed in this bilayer, with only partial asymmetry of the lipids. The proposed molecular architecture of the layered membranes of compact myelin fits such a concept (Fig. 4-11). Models of compact myelin are based on data from electron microscopy, immunostaining, X-ray diffraction, surface probes studies, structural abnormalities in mutant mice, correlations between structure and composition in various species, and predictions of protein structure from sequencing information [4]. 

The MBPs are extrinsic proteins localized exclusively at the cytoplasmic surface in the major dense line (Fig. 4-11), a conclusion based on their amino acid sequence, inaccessibility to surface probes and direct localization at the electron microscope level by immunocytochemistry. There is evidence to suggest that MBP forms dimers, and it is believed to be the principal protein stabilizing the major dense line of CNS myelin, possibly by interacting with negatively charged lipids. A severe hypomyelination and failure of compaction of the major dense line in MBP deficient shiverer mutants supports this hypothesis (Table 4-2). 

Figure 15.4 Four compounds that are methylated either by SAM or methyl FH4 (CH3 FH4). The processes are (i) cytidine bases in DNA (11) methylatlon of deoxyUMP to produce deoxythymidine monophosphate (111) formation of phosphatidylcholine from phos-phatldylethanolamlne (Chapter 17) (Iv) methylatlon of a protein In myelin. The base cytidine Is methylated In DNA to produce methylcytidine which. If deamlnated, produces methylthymidine In DNA. Methylatlon of the bases can modify gene transcription (see text). (PR 5 -phosphor1bose).

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