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JP25

Conformational Analysis for Oligopeptides using Hamiltonian Algorithm coupled with ab initio Molecular Orbital Calculation -Hydrogen-bond controlled conformational analysis-

○Hiroko Ieiri（Faculty of Science, Rikkyo University），Hiroaki Tokiwa（Faculty of Science, Rikkyo University），Umpei Nagashima（Grid Tecnology Research Center, National Institute of Advanced Industrial Science and Technology），Hiroaki Teramae（Depertment of Chemistry, Faculty of Science, Josai University）

Hydrogen bond and hydrophobic interaction are important to determine three-dimensional structure of protein. We analyzed conformational change of oligopeptides caused by intra-molecular hydrogen-bond formation and/or deformation using ab initio MO-MD method based on the Hamiltonian Algorithm at the HF/3-21G level. All initial conformations were assumed as alpha-helix structures. A glycine pentamer has two intra-molecular hydrogen bonds an initial alpha-helix conformation. One of these hydrogen bonds was formed between 1- and 4-residues, the other was between 2- and 5-residues. Both hydrogen bonds were deformed at around 3000 steps in an energy trajectory and new three intra-molecular hydrogen bonds were formed simultaneously. In the case of alanine pentamer, two hydrogen bonds between similar residues as a glycine pentamer exist at an initial conformation. These hydrogen bonds were deformed at earlier (about 1500) steps than the glycine pentamer. After 4000 steps, new hydrogen bond between 1- and 5-residues was furthermore formed. We also carried out the analysis for typical acidic oligopeptides such as asparatic and glutamic acids pentamers. Our proposed ab initio MO-MD method is efficient to theoretically analyze dynamical process of hydrogen-bond formation/deformation in oligopeptides.