Computational analysis of stability of the β-sheet structure

Ab initio quantum chemical calculations were carried out on the main factor responsible for the formation of beta-sheet structures in specific regions of proteins. Geometry optimization was performed at the Hartree-Fock level using a 3-21G** basis functional set. Total energies of alpha-helix and beta-sheet structures were compared using several types of computational models. The computational models for the beta-sheet structure were constructed by extracting a part of the protein from X-ray crystallographic data of HIV-1 or myosin, and the computational models for the alpha-helix structure were constructed by modifying the model for the beta-sheet structure. The results of computations indicated that all helix-like structures were more stable than were the beta-sheet structures under the condition of absence of any other molecules. On the other hand, all of the beta-sheet structures became more stable than the helix-like structures when water molecules existed around them. This finding suggests that beta-sheet structures are stabilized by the presence of water molecules and are primarily determined by local interaction among several neighboring residues.