Unfolding of tertiary structures of proteins.

The unfolding pathway of lysozyme was investigated by carrying out the computer simulation. Taking into account the simultaneous change of both the dihedral angels phi and psi of a residue, we explore the detailed features of the conformational energy profiles. The triangle distance map shows that the lysozyme molecule is divided into three domains, 1-40, 41-101 and 102-129 in amino acid residue numbers (referred to as the domains I, II and III, respectively). The calculated unfolding process indicates that in the early stage of unfolding domain III located at the C-terminal begins to be detached from the other two, and then domain I can be unfolded. The long-range interactions between domains I and III stabilize the whole molecule and give the cooperative nature of the folding. The calculated unfolding pathway of lysozyme is consistent with the folding pathway proposed by Anderson & Wetlaufer [J. Biol. Chem. (1976). 251, 3147-3153] who identified the disulfide bondings in the early stage of the glutathione regeneration. A simplified treatment of unfolding for myoglobin is also discussed in the Appendix.