Photoinduced Electron Transfer in Pentapeptide His-Asp-Ser-Gly-Tyr: Role of Chirality and Self-Association

Abstract

Factors governing electron transfer (ET) in proteins and peptides are widely studied due to the role of ET in biologically important processes. One of them is the influence of the optical configuration of amino acids on the ability of peptides to aggregate into ensembles: dimers, oligomers, fibrils. Such assemblies, called amyloids, are known to contain D-isomers of asparagine and serine, and their presence in aging living organisms leads to a number of diseases, including Alzheimer's disease. However, how these amino acids affect the structure and properties of peptides have not yet been established. Using the example of the pentapeptide (PP)-(L)histidine-(L)asparagine-(L)serine-glycine-(L)tyrosine and its analogues with D-asparagine and D-serine, this article studies the comparative reactivity of optical isomers in photoinduced ET using chemically induced dynamic nuclear polarization (CIDNP), fluorescence spectroscopy and quantum chemical calculations. The CIDNP method was chosen because it had previously demonstrated high sensitivity to ET processes in chiral dyads linked by non-covalent interactions. ET involving Tyr and His residues of PP was detected under UV irradiation both in the presence of an electron acceptor, naproxen, and during photolysis of PP itself. It was shown that the efficiency of ET and PP fluorescence quenching differ for optical isomers of asparagine and serine. In addition, the dependence of the CIDNP efficiency on the PP concentration showed that ET between Tyr and peptide bonds can occur in the dimer of the PP. Quantum chemical calculation confirm the possibility of PP self-association.

Keywords: Peptides, optical isomers, electron transfer, NMR, CIDNP, fluorescence