MYELIN PROTEINS

MYELIN PROTEINS:

Myelin proteins, which comprise 30% dry weight of myelin, are for most of the known ones, specific components of myelin and oligodendrocytes (Baumann et al., 1983). The major CNS myelin proteins MBP and PLP (and isoform DM-20) are low-molecular-weight proteins and constitute 80% of the total proteins. Another group of myelin proteins, insoluble after solubilization of purified myelin in chloroform- methanol 2:1, have been designated as the Wolfgram proteins, since their existence was suspected already in 1966 by Wolfgram (Wolfgram, 1966). These proteins comprise the CNP and other proteins. Several glycoproteins are present in myelin (Quarles, 1997), among which are MAG and MOG. Other proteins have also been identified, some of which have enzyme activities.

FIG. 5. Myelinating glial cells, myelin structure, and composition in the peripheral nervous system (PNS) and in the CNS. In the PNS, the myelinating Schwann cell myelinates only one segment of axon (top left corner), whereas in the CNS (top right corner), the oligodendrocyte is able to myelinate several axons. The compact myelin is formed by the opposition of the external faces of the membrane of the myelinating cell, forming the “double intraperiodic line”; the opposition of the internal faces followed by the extrusion of the cytoplasm, form the “major dense line.” The myelin proteins are schematically described; they differ between PNS and CNS. [Adapted from Pham-Dinh]

The large number of glycoproteins associated with central-nervous-system myelin suggests an unsuspected complexity in the interactions involved in the development and maintenance of plasma membrane.