Virtual Molecule: P0 Myelin Glycoprotein. I. Homology Modeling and Prediction of the Secondary and Tertiary Structure - Molecules: Nucleation, Aggregation and Crystallization - page 251

Fig. 10. Four steps of the P0_Ex protein opening (columns A, B C and D) caused by
disulfide bridge breaking and interactions with detergent (Sedzik et al ., 1999). The cartoon
models of P0_Ex presented in row I are colored green to represent hydrophilicity. The two
cysteines creating the disulfide bond are represented as VDW spheres and are visible in
the center of the molecule. The 28 Trp on the top of the model is colored red. The two
tryptophans participating in dimer and tetramer creation by molecular associations
observed in crystals of P0_Ex (Shapiro et al ., 1996) are shown as a stick model. The space-
filling models colored in accordance with the Kyte, Doolittle (1982) hydrophobicity scale
(hydrophobic residues — red spectrum; hydrophilic residues — blue spectrum) are shown
in row II. Hydrophilic residues located on the external surface of molecule (blue) are
clearly visible in IIA and IIIA. The hydrophobic core of the P0_Ex molecule is uncovered
during opening (rows II and III, columns B, C and D). The hydrophobic pocket is consti-
tuted during this process (the red region in rows II and III).
This S-S bridge can be disrupted during SDS-PAGE electrophore-
sis causing P0 molecules to migrate in the electrostatic field more
slowly, indicating the higher molecular weight of 3 kDa (Sedzik et al .,
1997).