title: Redox-induced conformational switching in photosystem-II-inspired biomimetic peptides: a UV resonance Raman study.
abstract: Long-distance electron transfer (ET) plays a critical role in solar energy conversion, DNA synthesis, and mitochondrial respiration. Tyrosine (Y) side chains can function as intermediates in these reactions. The oxidized form of tyrosine deprotonates to form a neutral tyrosyl radical, Y(•), a powerful oxidant. In photosystem II (PSII) and ribonucleotide reductase, redox-active tyrosines are involved in the proton-coupled electron transfer (PCET) reactions, which are key in catalysis. In these proteins, redox-linked structural dynamics may play a role in controlling the radical's extraordinary oxidizing power. To define these dynamics in a structurally tractable system, we have constructed biomimetic peptide maquettes, which are inspired by PSII. UV resonance Raman studies were conducted of ET and PCET reactions in these β-hairpins, which contain a single tyrosine residue. At pH 11, UV photolysis induces ET from the deprotonated phenolate side chain to solvent. At pH 8.5, interstrand proton transfer to a π-stacked histidine accompanies the Y oxidation reaction. The UV resonance Raman difference spectrum, associated with Y oxidation, was obtained from the peptide maquettes in D(2)O buffers. The difference spectra exhibited bands at 1441 and 1472 cm(-1), which are assigned to the amide II' (CN) vibration of the β-hairpin. This amide II' spectral change was attributed to substantial alterations in amide hydrogen bonding, which are coupled with the Y/Y(•) redox reaction and are reversible. These experiments show that ET and PCET reactions can create new minima in the protein conformational landscape. This work suggests that charge-coupled conformational changes can occur in complex proteins that contain redox-active tyrosines. These redox-linked dynamics could play an important role in control of PCET in biological oxygen evolution, respiration, and DNA synthesis.
authors.affiliation: School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
authors.forename: Cynthia V
authors.initials: CV
authors.lastname: Pagba
authors.forename: Bridgette A
authors.initials: BA
authors.lastname: Barry
mesh_terms: D000595:Amino Acid Sequence; D040761:Biomimetic Materials / Q000737:chemistry* / Q000378:metabolism; D017666:Deuterium Oxide / Q000737:chemistry; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D010782:Photolysis; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D011522:Protons; D012997:Solvents / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D014443:Tyrosine / Q000737:chemistry
chemical_list: D010455:Peptides; D045332:Photosystem II Protein Complex; D011522:Protons; D012997:Solvents; D014443:Tyrosine; D017666:Deuterium Oxide