title: Computational insights into the charge relaying properties of β-turn peptides in protein charge transfers.
abstract: Density functional theory calculations suggest that β-turn peptide segments can act as a novel dual-relay elements to facilitate long-range charge hopping transport in proteins, with the N terminus relaying electron hopping transfer and the C terminus relaying hole hopping migration. The electron- or hole-binding ability of such a β-turn is subject to the conformations of oligopeptides and lengths of its linking strands. On the one hand, strand extension at the C-terminal end of a β-turn considerably enhances the electron-binding of the β-turn N terminus, due to its unique electropositivity in the macro-dipole, but does not enhance hole-forming of the β-turn C terminus because of competition from other sites within the β-strand. On the other hand, strand extension at the N terminal end of the β-turn greatly enhances hole-binding of the β-turn C terminus, due to its distinct electronegativity in the macro-dipole, but does not considerably enhance electron-binding ability of the N terminus because of the shared responsibility of other sites in the β-strand. Thus, in the β-hairpin structures, electron- or hole-binding abilities of both termini of the β-turn motif degenerate compared with those of the two hook structures, due to the decreased macro-dipole polarity caused by the extending the two terminal strands. In general, the high polarity of a macro-dipole always plays a principal role in determining charge-relay properties through modifying the components and energies of the highest occupied and lowest unoccupied molecular orbitals of the β-turn motif, whereas local dipoles with low polarity only play a cooperative assisting role. Further exploration is needed to identify other factors that influence relay properties in these protein motifs.
authors.affiliation: Institute of Theoretical Chemistry, School of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100 (P.R. China).
authors.forename: Ru
authors.initials: R
authors.lastname: Zhang
authors.forename: Jinxiang
authors.initials: J
authors.lastname: Liu
authors.forename: Hongfang
authors.initials: H
authors.lastname: Yang
authors.forename: Shoushan
authors.initials: S
authors.lastname: Wang
authors.forename: Meng
authors.initials: M
authors.lastname: Zhang
authors.forename: Yuxiang
authors.initials: Y
authors.lastname: Bu
mesh_terms: D004583:Electrons; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D009842:Oligopeptides; D011506:Proteins
keywords: charge relay; density functional theory calculations; ionization potential; spin density distribution; β-turn oligopeptides