Myelin Basic Protein, A Saucy Molecule With High Responsiveness to the Environment or Just an Unusual Membrane Protein? - Molecules: Nucleation, Aggregation and Crystallization - page 174

Introduction
The physiological environment of MBP is the myelin membrane. About
95% of MBP is associated with lipids and requires a detergent for its
extraction. The membrane-bound MBP can be found within or outside
lipid rafts, depending on methylation, phosphorylation, deimidation and
other chemical modifications of its residues. Part of MBP cannot be
extracted even with SDS and urea. In all lipid-bound MBP preparations,
the protein appears to be structured. Thus, MBP structure could be best
analyzed after reincorporation of the protein in liposomes made of
myelin lipids. In conclusion, rather than being an intrinsic unstructured
protein, as suggested in recent years, MBP is a membrane protein with an
easily modifiable structure.
The classic acid-extracted, water-soluble MBP is really a mixture of
different isomers, and this might explain why MBP has never been crys-
tallized. New crystallization attempts could be made using as starting
material the protein purified from specific membrane microdomains,
since in this case MBP may have the same post-translational modifica-
tions and be more homogeneous. Then, the knowledge of MBP structure
will lead to a better understanding of myelin structure and of its degrada-
tion in demyelinating diseases.
Myelin Basic Protein: What Is It and What Does It Do?
The myelin sheath of the central nervous system (CNS) is the lipid-rich,
multi-lamellar membrane process extending from the oligodendrocytes
to cover all around segments of the nerve axon and to facilitate rapid
and efficient nerve conduction (Kirschner, Blaurock, 1992; Moscarello,
1996).
Myelin basic protein (MBP) is the second major protein in CNS
myelin and perhaps the most studied among its components (Smith, 1992;
Harauz et al ., 2004). Human MBP is present in different isoforms — of
17, 18.5, 20.2, 21.5 kDa — deriving from the alternate splicing of the
mRNA transcript (Givogri et al ., 2000). The MBP gene, which is made of
seven exons, belongs to the larger Golli gene (Givogri et al ., 2001).