Principles of protein architecture.

The three-dimensional structure of a protein is governed by the thermodynamical principle established experimentally by Anfinsen, Isemura, and others. The rapidity of the folding process is another important key phenomenon. With these basics in mind an island model is proposed which requires a restricted folding pathway. A physicochemical method of the prediction of alpha-helices and beta-strands is also discussed. By virtue of the long-range hydrophobic interaction and the specific interactions between hydrophobic residues which are determined by the basic idea underlying the island model, one can fold the polypeptide chain into a tertiary structure upon determination of the secondary structures. Several examples of folding are presented. In myoglobin the heme group must be considered to reach the correct final tertiary structure. In lysozyme and phospholipase, the disulfide bondings are necessary to fasten the polypeptide chain. The selection of proper cysteine pairs among other possible ones is carried out by drawing the lampshades (locus of H atom of SH) of cysteines. In flavodoxin and thioredoxin the formation of parallel beta-structure from beta-strands is considered. The formations of antiparallel beta-structure in lysozyme and phospholipase are also discussed.