Energy transport in peptide helices

• Published in: Proceedings of the National Academy of Sciences - PNAS 2007-07, Vol.104 (31), p.12749-12754
• Main Authors: Botan, Virgiliu, Backus, Ellen H.G, Pfister, Rolf, Moretto, Alessandro, Crisma, Marco, Toniolo, Claudio, Nguyen, Phuong H, Stock, Gerhard, Hamm, Peter
• Format: Article
• Language: English
• Subjects: Atoms; Biological Sciences; Biophysics; Cells; Computer Simulation; Crystallography, X-Ray; Energy; Energy transfer; Functional groups; Heat; Heaters; Hydrogen bonds; Kinetic energy; Models, Molecular; Molecular biology; Molecules; Peptides; Peptides - chemistry; Peptides - metabolism; Protein Structure, Secondary; Protein Structure, Tertiary; Simulation; Solvents; Spectrum Analysis; Time Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0701762104

We investigate energy transport through an α-aminoisobutyric acid-based 3₁₀-helix dissolved in chloroform in a combined experimental-theoretical approach. Vibrational energy is locally deposited at the N terminus of the helix by ultrafast internal conversion of a covalently attached, electronically excited, azobenzene moiety. Heat flow through the helix is detected with subpicosecond time resolution by employing vibrational probes as local thermo meters at various distances from the heat source. The experiment is supplemented by detailed nonequilibrium molecular dynamics (MD) simulations of the process, revealing good qualitative agreement with experiment: Both theory and experiment exhibit an almost instantaneous temperature jump of the reporter units next to the heater which is attributed to the direct impact of the isomerizing azobenzene moiety. After this impact event, helix and azobenzene moiety appear to be thermally decoupled. The energy deposited in the helix thermalizes on a subpicosecond timescale and propagates along the helix in a diffusive-like process, accompanied by a significant loss into the solvent. However, in terms of quantitative numbers, theory and experiment differ. In particular, the MD simulation seems to overestimate the heat diffusion constant (2 Ų ps⁻¹ from the experiment) by a factor of five.