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MBP Ligands and Functions
On the other hand, when looking to its capability to bind a number of
different ligands (Campagnoni, Skoff, 2001), MBP appears to be a good
candidate as an IUP. MBP can bind many divalent cations, in particular
zinc, a physiological ligand present in myelin (Earl et al ., 1991;
Cavatorta et al ., 1994; Riccio et al ., 1995; Tsang et al ., 1997). MBP can
also bind small molecules such as the heme group (Vacher et al ., 1984;
Morris et al ., 1987); azo compounds (Liebes et al ., 1976); serotonin and
hallucinogens (Alivisatos et al ., 1971; Carnegie et al ., 1972) and GTP
(Chan et al ., 1988).
Binding of MBP to detergent and lipids has been studied in depth,
although MBP was considered to be an extrinsic, lipid-free and water-
soluble protein (Riccio et al ., 1984; Smith 1992; Riccio, Quagliariello,
1993; Beniac et al ., 1997; Hu et al ., 2004; Harauz et al ., 2004). MBP can
also bind to other myelin proteins: myelin proteolipid protein [(PLP) (Golds,
Braun, 1978; Boggs, Wang, 2004)], and myelin 2
,3
-cyclic nucleotide
-phosphodiesterase [(CNP) (Dyer, Benjamins, 1989; Richter-Landsberg,
2001)]. MBP can bind to polyanionic proteins: calmodulin [(CaM) (Chan
et al ., 1994; Polverini et al ., 2004)]; actin (Barylko, Dobrowolski, 1984;
Boggs et al ., 2005); tubulin (Modesti, Barra, 1986; Gendreau et al ., 2003)
and clathrin (Boggs, 2006). MBP can also bind to alfa 2 -macroglobulin
(Gunnarson et al ., 1998, 2003) and heat shock protein 70 (Aquino et al .,
1998; Cwiklinska et al ., 2003). Adherence of MBP to T cells has been
reported (Bobba et al ., 1991).
According to their ability to interact with different ions, molecules
and cells, all MBP isoforms seem to fulfil different functions in
myelin (Boggs, 2006), and seem to be involved also in apparently
unrelated activities outside the CNS (Harauz et al ., 2004). In fact,
besides the main role in compacting myelin, MBP may be involved
in various different functions, such as modulation of signal transduc-
tion pathways (Dyer, 1997; Campagnoni et al ., 2003), and induction of
insulin and glucagon release from the pancreas (Kolehmainen,
Sormunen, 1998).
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