title: Distance dependence of electron transfer across peptides with different secondary structures: the role of Peptide energetics and electronic coupling.
abstract: The charge-transfer transition energies and the electronic-coupling matrix element, |H(DA)|, for electron transfer from aminopyridine (ap) to the 4-carbonyl-2,2'-bipyridine (cbpy) in cbpy-(gly)(n)-ap (gly = glycine, n = 0-6) molecules were calculated using the Zerner's INDO/S, together with the Cave and Newton methods. The oligopeptide linkages used were those of the idealized protein secondary structures, the alpha-helix, 3(10)-helix, beta-strand, and polyproline I- and II-helices. The charge-transfer transition energies are influenced by the magnitude and direction of the dipole generated by the peptide secondary structure. The electronic coupling |H(DA)| between (cbpy) and (ap) is also dependent on the nature of the secondary structure of the peptide. A plot of 2.ln|H(DA)| versus the charge-transfer distance (assumed to be the dipole moment change between the ground state and the charge-transfer states) showed that the polyproline II structure is a more efficient bridge for long-distance electron-transfer reactions (beta = 0.7 A(-1)) than the other secondary structures (beta approximately 1.3 A(-1)). Similar calculations on charged dipeptide derivatives, [CH(3)CONHCH(2)CONHCH(3)](+/)(-), showed that peptide-peptide interaction is more dependent on conformation in the cationic than in the anionic dipeptides. The alpha-helix and polyproline II-helix both have large peptide-peptide interactions (|H(DA)| > 800 cm(-1)) which arise from the angular dependence of their pi-orbitals. Such an interaction is much weaker than in the beta-strand peptides. These combined results were found to be consistent with electron-transfer rates experimentally observed across short peptide bridges in polyproline II (n = 1-3). These results can also account for directional electron transfer observed in an alpha-helical structure (different ET rates versus the direction of the molecular dipole).
authors.affiliation: Department of Chemistry, Rutgers, the State University of New Jersey, Piscataway 08855, USA.
authors.forename: Yeung-gyo K
authors.initials: YG
authors.lastname: Shin
authors.forename: Marshall D
authors.initials: MD
authors.lastname: Newton
authors.forename: Stephan S
authors.initials: SS
authors.lastname: Isied
mesh_terms: D015082:2,2'-Dipyridyl / Q000031:analogs & derivatives / Q000737:chemistry; D004151:Dipeptides / Q000737:chemistry; D004583:Electrons; D008956:Models, Chemical; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013816:Thermodynamics
chemical_list: D004151:Dipeptides; D009842:Oligopeptides; D010455:Peptides; C011080:polyglycine; D015082:2,2'-Dipyridyl