Myelin Basic Protein, A Saucy Molecule With High Responsiveness to the Environment or Just an Unusual Membrane Protein? - Molecules: Nucleation, Aggregation and Crystallization - page 180

remained poorly organized (Riccio et al ., 1986, 2000). A comparison
between LF-MBP and LB-MBP has been discussed (Riccio, Quagliariello,
1993).
Partitioning of MBP in the Myelin Membrane
According to the new model of biological membranes proposed by
Simons (Simons, Ikonen, 1997), it was shown that myelin is made of lipid
platforms consisting of glycosphingolipids and cholesterol microdomains
called lipid rafts , moving in a more fluid non-raft region consisting preva-
lently of glycerophospholipids (Taylor et al ., 2002). Lipid rafts can be
involved in a series of biological process, such as signal transduction
pathways, apoptosis, cell adhesion, and protein sorting (Brown, London,
1998; Simons, Toomre, 2000).
Raft and non-raft microdomains are usually recognized by their dif-
ferent solubility in detergents. Non-raft microdomains are soluble in mild
detergents as CHAPS or Triton-X100, whereas lipid rafts are not.
Accordingly, purified myelin proteins extracted with CHAPS have been
found to be associated mainly with glycerophospholipids such as PS and
PE. LB-MBP was the first example of a myelin protein belonging to the
non-raft microdomains.
Further studies have shown that MBP is distributed in all different
microdomains of myelin (DeBruin et al ., 2005; DeBruin, Harauz, 2007).
Accordingly with this finding, we have extracted different MBPs from
myelin under different conditions. First of all, MBP was extracted with
salts (0.5 M NaCl) ( salt-extracted MBP ). The second treatment was based
on the use of CHAPS to extract MBP from the salt-treated myelin residue
( non-raft LB-MBP ). Thereafter, the CHAPS residue was treated with SDS
to extract MBP from the raft domains ( soluble raft LB-MBP ). Part of MBP
was not extracted at all and remained in the so-called hyper-raft domain.
As assessed by high performance thin layer chromatography (HPTLC), all
MBPs extracted with detergents or present in the detergent-insoluble
hyper-raft domain, were found to be associated to lipids, but the lipid pattern
was different. Non-raft MBP (the classical LB-MBP) was extracted and