title: Electronic structures of Ascaris trypsin inhibitor in solution.
abstract: The electronic structures of Ascaris trypsin inhibitor in solution are obtained by the first-principles, all-electron, ab initio calculation using the self-consistent cluster-embedding (SCCE) method. The inhibitor, made up of 62 amino acid residues with 912 atoms, has two three-dimensional solution structures: 1ata and 1atb. The calculated ground-state energy of structure 1atb is lower than that of structure 1ata by 6.12 eV. The active sites are determined and explained: only structure 1atb has a N terminal at residue ARG+31. This shows that the structure 1atb is the stable and active form of the inhibitor, which is in agreement with the experimental results. The calculation reveals that some parts of the inhibitor can be easily changed while the inhibitor's biological activity may be kept. This kind of information may be helpful in fighting viruses such as AIDS, SARS, and flu, since these viruses have higher variability. The calculation offers an independent theoretical estimate of the precision of structure determination.
authors.affiliation: Pohl Institute of Solid State Physics, Tongji University, Shanghai 200092, China. zhenghp@mail.tongji.edu.cn
authors.forename: Haoping
authors.initials: H
authors.lastname: Zheng
mesh_terms: D000818:Animals; D001200:Ascaris / Q000378:metabolism*; D001665:Binding Sites; D004583:Electrons; D007091:Image Processing, Computer-Assisted; D008958:Models, Molecular; D015233:Models, Statistical; D017434:Protein Structure, Tertiary