Article

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.

Research Institute, The Hospital for Sick Children, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada.
Journal of Neuroscience Research (impact factor: 2.74). 11/2002; 70(1):8-23. DOI:10.1002/jnr.10383 pp.8-23
Source: PubMed

ABSTRACT 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.

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Keywords

2'3'-cyclic nucleotide 3'-phosphodiesterase
 
30 kDa phosphoserine-containing protein
 
anti-MAG monoclonal antibodies
 
anti-PLP
 
immunoprecipitated complex
 
large MAG isoform L-MAG
 
large membrane fragment
 
Lipid analysis
 
major myelin proteins
 
myelin proteins
 
myelin-associated glycoprotein
 
myelin-axonal interactions
 
phosphotyrosine-containing proteins
 
PLP-MBP-S-MAG coimmunoprecipitated
 
PLP-MBP-S-MAG complex
 
protein complexes
 
Sepharose CL6B column
 
small isoform
 
small PLP isoform DM20
 
sucrose density gradient sedimentation