Bioinformatics of Myelin Membrane Proteins - Molecules: Nucleation, Aggregation and Crystallization - page 47

membrane, and regions around residues 40-59, 178-191 and 215-232 to
the extracellular side. Disulfide bonds are thought to form between
residues 184-228 and 201-220, suggesting an extracellular location for
these residues. Taken together, the data strongly suggests an N in -4TM-C in
topology with both termini in the cytosol, cf. Wahle, Stoffel (1998). The
DM-20 isoform lacks residues 117-151 in the central cytosolic loop.
Proteolipid is implicated in Pelizaeus-Merzbacher disease, a neurological
condition that affects myelin (insulation surrounding the axons) in the
brain and spinal cord. The symptoms are first noticed shortly after birth or
in infancy (Garbern et al ., 1999). There is no known cure for this disease.

MAG

Human MAG (Uniprot P20916) is 626 residues long, including a strongly
predicted N-terminal signal peptide (residues 1-19) and a very stable
transmembrane -helix (Fig. 6). It carries multiple N-linked glycans and

disulfide bonds in the first 500 residues (consistent with an extracellular
location of this region). The topology of the mature protein (after removal
of the signal peptide) is hence N out -1TM-C in .

α

MOG

Human MOG (Uniprot Q16653) is 247 residues long, including a strongly
predicted N-terminal signal peptide (residues 1-29) and two C-terminal
hydrophobic segments (Fig. 7). It carries a potential N-linked glycan at
residue 60 and a potential disulfide between residues 53 and 127 (consis-
tent with an extracellular location of this region). The most C-terminal
hydrophobic domain is lacking in a number of isoforms of the protein.
Available biochemical data suggest that only the first of the two
hydrophobic domains forms a transmembrane -helix, and that the

C-terminus is cytosolic (della Gaspera, 1998). The topology of the mature
protein (after removal of the signal peptide) is hence N out -1TM-C in . Given

α