Virtual Molecule: P0 Myelin Glycoprotein. I. Homology Modeling and Prediction of the Secondary and Tertiary Structure - Molecules: Nucleation, Aggregation and Crystallization - page 250

Fig. 9. Four projections of the extracellular part of the P0 protein: (B) from the top/from the
next lipid bilayer side and (C) from the bottom/from the membrane side. The disulfide bridge
21 Cys-S—S- 98 Cys is shown as a stick model and is visible in the central part of protein
(A)-(D). Breaking the disulfide bridge (marked with orange arrows) can result in the opening
of the molecule and uncover the strongly hydrophobic core of the protein. Three functional
parts for the opening of the P0_Ex subunit are shown. The green colored part of this model is
the stable and anchored lipid bilayer; this part does not move during the opening process. The
blue colored part is movable after taking up the 21 Cys-S—S- 98 Cys bond, because it is linked
with the unmovable part by the single flexible and longest loop of the P0_Ex subunit (red).
bridge strongly stabilizes the 3D structure of the protein and its disruption
can change the spatial conformation of the polypeptide chain causing dys-
function of the whole molecule. The disulfide bridge brings together the
short part of the extracellular domain (24 a.a.: 1 Ile … 24 Trp) with the
biggest part of the P0_Ex subunit (Figs. 3 and 9). The long ( 25 Ser … 33 Ile)
and dynamic loop, is stabilized by the hydrophobic interaction between
28 Trp and the membrane (Shapiro et al ., 1996), and links the first 24-a.a.-
long part with the large and stable remainder of the subunit anchored in
the membrane (Figs. 7(A), 9 and 10).