T. Kim et Se. Pfeiffer, Myelin glycosphingolipid/cholesterol-enriched microdomains selectively sequester the non-compact myelin proteins CNP and MOG, J NEUROCYT, 28(4-5), 1999, pp. 281-293
Plasma membranes are complex arrays of protein and lipid subdomains. Deterg
ent-insoluble, glycosphingolipid/cholesterol-enriched micro-domains (DIGCEM
s) have been implicated in protein sorting and/or as sites for signaling ca
scades in the plasma membrane. We previously identified the presence of DIG
CEMs in oligodendrocytes in culture and purified myelin and characterized a
novel DIGCEM-associated tetraspan protein, MVP17/rMAL (Kim et al. (1995) J
ournal of Neuroscience Research 42, 413-422). We have now analyzed the asso
ciation of known myelin proteins with DIGCEMs in order to provide a better
understanding of their roles during myelin biogenesis. We used four well-es
tablished criteria to identify myelin DIGCEM-associated proteins: insolubil
ity in a non-ionic detergent Triton X-100 at low temperature (4 degrees C),
flotation of the insoluble complexes to low density fractions in sucrose g
radients, and TX-100 solubilization at 37 degrees C, or at 4 degrees C foll
owing treatment with the cholesterol-binding detergent saponin. We demonstr
ate that these proteins fall into four distinct groups. Although all tested
proteins could be floated to a low-density fraction, proteolipid protein (
PLP), myelin basic protein (MBP) and myelin associated glycoprotein (MAG) w
ere solubilized by the detergent extraction, and connexin32 (Cx32) and olig
odendrocyte-specific protein (OSP) met only some of the criteria for DIGCEM
s. Only the non-compact myelin proteins 2',3'-cyclic nucleotide 3'-phosphod
iesterase (CNP) and myelin/oligodendrocyte glycoprotein (MOG) satisfied all
four criteria for DIGCEM-associated proteins. Significantly, only similar
to 40% of CNP and MOG were selectively associated with DIGCEMs. This sugges
ts that they may have both non-active "soluble", and functionally active DI
GCEM-associated, forms in the membrane, consistent with current views that
DIGCEMs provide platforms for bringing together and activating components o
f the signal transduction apparatus. We therefore propose that CNP and MOG
may have unique roles among the major myelin proteins in signaling pathways
mediated by lipid-protein microdomains formed in myelin.