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Poster Presentations

Ph.D./Postdoc Poster Presentation

PPP01

Tryptophan-tyrosine Interactions in Photosystem II- and Ribonucleotide Reductase-inspired Beta Hairpins

Tyler G. McCaslin1,2, Cynthia V. Pagba1,2, San-Hui Chi1,3, Hyea J. Hwang4, James C. Gumbart1,2,5, Joseph W. Perry1,3, Cristina Oliveri6,7, Fernando Porcelli8, Gianluigi Veglia6.7, Zhanjun Guo1,2  ,Miranda McDaniel1,2, and Bridgette A. Barry1,2,*

1School of Chemistry and Biochemistry, 2The Parker H. Petit Institute of Bioengineering and Bioscience, 3Center of Organic Photonics and Electronics, 4School of Materials Science and Engineering,5School of Physics, Georgia Institute of Technology, Atlanta, GA 30332; 6Department of Biochemistry, Molecular Biophysics, and Biophysics, and 7Department of Chemistry, University of Minnesota, St. Paul, Minnesota 55455; 8Department of Environmental Sciences, University of Tuscia, Viterbo, Italy, *Email: bb213@mail.gatech.edu

Tyrosine and tryptophan play essential roles in biological proton coupled electron transfer (PCET).  In this process, oxidation of tyrosine or tryptophan is associated with movement of a proton.  PCET is essential in photosynthesis and DNA synthesis.  To elucidate the factors that control the rate and energetics of PCET reactions in such complex enzymes, we have designed, synthesized, and characterized reactions in a structurally well-defined family of 18-mer peptides, which conduct tyrosine/tryptophan-based PCET (Sibert et al 2007, Pagba et al 2015). The tyrosine or tryptophan is oxidized either electrochemically or by UV photolysis.  In this model system, the peptides fold to give a beta hairpin, and cross-strand interactions are tuned to control the reactivity of the aromatic side chain.  The structures of the peptides are determined with NMR spectroscopy. Molecular dynamics simulations are used to evaluate the effect of sequence variation and tyrosine charge state on peptide structure. A combination of techniques, including electron paramagnetic resonance, UV resonance Raman, and circular dichroism spectroscopies, is employed to study the structure of the radical and singlet states.  Time-resolved absorption spectroscopy was used to evaluate the effect of non-covalent interactions on the rate of excited state decay. A unique cross-strand interaction, which alters the physiochemical properties, is observed in tyrosine and tryptophan containing peptides.  The biological relevance will be discussed.

Figure 1. Frame from molecular dynamics simulation of Peptide MW13A14 illustrating a cross-strand Y5-W13 interaction.

Sibert R, Josowicz M, Porcelli F, Veglia G, Range K, and Barry BA (2007) J. Am. Chem. Soc., 129, 4393-4400.

Pagba CV, McCaslin TG, Veglia G, Porcelli F, Yohannan J, Guo Z, McDaniel M, and Barry BA (2015) Nat. Commun., 6, 10100.