Computational Insights into the Charge Relaying Properties of β-Turn Peptides in Protein Charge Transfers

• Published in: Chemphyschem 2015-02, Vol.16 (2), p.436-446
• Main Authors: Zhang, Ru, Liu, Jinxiang, Yang, Hongfang, Wang, Shoushan, Zhang, Meng, Bu, Yuxiang
• Format: Article
• Language: English
• Subjects: charge relay; density functional theory calculations; Electrons; ionization potential; Models, Molecular; Oligopeptides - chemistry; Protein Structure, Secondary; Protein Structure, Tertiary; Proteins - chemistry; Quantum Theory; spin density distribution; β-turn oligopeptides
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201402657

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. Take it in turns: β‐Turn peptide segments can act as 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 conformations and lengths of the linking strands considerably modify charge mediation due to variation in polarity of the macro‐dipole. This work might further the understanding of long‐range charge‐transfer mechanisms in proteins.