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In-Depth Information
In particular, the 18.5 kDa MBP, the major human isoform, is an inter-
esting protein to study for different reasons:
(i) It is believed to have the key role of biological “glue” in the forma-
tion, compaction and maintenance of the multi-lamellar structure of
the myelin sheath (Privat
et al
., 1979; Riccio
et al
., 1986; Readhead
et al
., 1987; Riccio
et al
., 2000).
(ii) It is a candidate autoantigen in the context of multiple sclerosis (MS)
research, since it can induce the Experimental Allergic Encephalo-
myelitis (EAE), an animal model of MS (Alvord
et al
., 1984; Massacesi
et al
., 1993; Gold
et al
., 2006).
(iii) Its possible relationship with the IUPs, the “intrinsically unstruc-
tured proteins” or “natively unfolded proteins” (Harauz
et al
.,
2004) and the difficulty to achieve its crystallization (Sedzik,
Kirschner, 1992).
The IUPs
IUPs (intrinsically unstructured proteins) are proteins lacking a precise
folded structure (Wright, Dyson, 1999; Tompa, 2002). Under physiologi-
cal conditions (the native and functional state), IUPs are present with a
highly flexible, random coil structure but are prone to adopt a folded con-
formation upon binding to different ligands and consequently switch to
distinct, unrelated functions (Tompa, 2005). Structural disorder is then
the basis for a protein to fulfil different tasks. In general, IUPs are mainly
hydrophilic, charged molecules, and do not possess a hydrophobic core.
Their amino acid composition is different from the average amino acid
distribution of globular proteins reported in the Protein Data Bank
(Dawson
et al
., 2003).
The assignment of MBP to the IUPs was made on the basis of its
high net charge, low hydrophobicity and the claimed absence of struc-
ture in the native form (Harauz
et al
., 2004). However, with respect to
amino acid usage, MBP differs from IUPs in the content of A, R, E, G,
H, F and V.
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