Myelin proteolipid protein, basic protein, the small isoform of myelin-associated glycoprotein, and p42MAPK are associated in the Triton X-100 extract of central nervous system myelin.
To further our understanding of the functions of the major myelin proteins, myelin basic protein (MBP) and proteolipid protein (PLP), and other myelin proteins, such as 2'3'-cyclic nucleotide 3'-phosphodiesterase (CNP) and myelin-associated glycoprotein (MAG), bovine brain myelin was extracted with Triton X-100, and protein complexes in the detergent-soluble fraction were isolated by coimmunoprecipitation and sucrose density gradient sedimentation. MBP, PLP, and the small isoform of MAG (S-MAG) were coimmunoprecipitated from the detergent-soluble fraction by anti-PLP, anti-MBP or anti-MAG monoclonal antibodies. Additionally, a 30 kDa phosphoserine-containing protein and two phosphotyrosine-containing proteins (M(r) 30 and 42 kDa) were found in the coimmunoprecipitates. The 42 kDa protein is probably p42MAPK, in that MAPK was shown also to be present in the immunoprecipitated complex. CNP, the small PLP isoform DM20, the large MAG isoform L-MAG, MOG, CD44, MEK, p44MAPK, and actin were not present in the immunoprecipitates, although they were present in the detergent-soluble fraction. Lipid analysis revealed that the PLP-MBP-S-MAG coimmunoprecipitated with some phospholipids and sulfatide but not cholesterol or galactosylceramide. However, the complex had a high density, indicating that the lipid/protein ratio is low, and it was retained on a Sepharose CL6B column, indicating that it is not a large membrane fragment. Given that MAG is localized mainly in the periaxonal region of myelin, where it interacts with axonal ligands, the PLP-MBP-S-MAG complex may come from these regions, where it could participate in dynamic functions in the myelin sheath and myelin-axonal interactions.
Arvanitis
Dina N
DN
Research Institute, The Hospital for Sick Children, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada.
Yang
Wenhong
W
Boggs
Joan M
JM
D000818:Animals; D015153:Blotting, Western; D002417:Cattle; D002457:Cell Extracts / Q000737:chemistry; D002490:Central Nervous System / Q000737:chemistry*; D002499:Centrifugation, Density Gradient / Q000379:methods; D002850:Chromatography, Gel / Q000379:methods; D015151:Immunoblotting; D019950:Mitogen-Activated Protein Kinase 1 / Q000032:analysis*; D004676:Myelin Basic Protein / Q000032:analysis*; D018991:Myelin Proteolipid Protein / Q000032:analysis*; D018992:Myelin-Associated Glycoprotein / Q000032:analysis; D017830:Octoxynol; D010768:Phosphoserine / Q000032:analysis; D019000:Phosphotyrosine / Q000032:analysis; D011233:Precipitin Tests / Q000379:methods; D012995:Solubility
D002457:Cell Extracts; D004676:Myelin Basic Protein; D018991:Myelin Proteolipid Protein; D018992:Myelin-Associated Glycoprotein; D010768:Phosphoserine; D019000:Phosphotyrosine; D017830:Octoxynol; D019950:Mitogen-Activated Protein Kinase 1