Abstract
The influence of hydration water on the vibrational energy relaxation in a protein holds the key to understand ultrafast protein dynamics, but its detection is a major challenge. Here, we report measurements on the ultrafast vibrational dynamics of amide I vibrations of proteins at the lipid membrane/H2O interface using femtosecond time-resolved sum frequency generation vibrational spectroscopy. We find that the relaxation time of the amide I mode shows a very strong dependence on the H2O exposure, but not on the D2O exposure. This observation indicates that the exposure of amide I bond to H2O opens up a resonant relaxation channel and facilitates direct resonant vibrational energy transfer from the amide I mode to the H2O bending mode. The protein backbone motions can thus be energetically coupled with protein-bound water molecules. Our findings highlight the influence of H2O on the ultrafast structure dynamics of proteins.
Highlights
The influence of hydration water on the vibrational energy relaxation in a protein holds the key to understand ultrafast protein dynamics, but its detection is a major challenge
Many major issues on this matter have not been addressed[3], for example, what are the roles of resonant vibrational energy transfer in proteins; is there a “shortcut” for energy to dissipate into the solvent? Because H2O is significantly different from D2O as solvents[12], the ultrafast protein dynamics in the two solvents could be quite different
We investigate the ultrafast vibrational dynamics of amide I mode of proteins at the H2O interface using a surface-sensitive pump–probe set-up in which a femtosecond IR pump is followed by a sum frequency generation vibrational spectroscopy (SFGVS) probe
Summary
The influence of hydration water on the vibrational energy relaxation in a protein holds the key to understand ultrafast protein dynamics, but its detection is a major challenge. We report measurements on the ultrafast vibrational dynamics of amide I vibrations of proteins at the lipid membrane/H2O interface using femtosecond time-resolved sum frequency generation vibrational spectroscopy. The study of vibrational energy dissipation between proteins and their surrounding water provides a powerful approach to unravel the nature of this dynamical coupling[3,8] and analyze protein structures or solvent accessibility[9,10]. We investigate the ultrafast vibrational dynamics of amide I mode of proteins at the H2O interface using a surface-sensitive pump–probe set-up in which a femtosecond IR pump is followed by a sum frequency generation vibrational spectroscopy (SFGVS) probe. We report measurements on the ultrafast vibrational dynamics of amide I vibrations of proteins at the lipid membrane/H2O interface using several peptides, including melittin, LKα14, mastoparan (MP), influenza M2 proteins (AM2 and BM2), and KALP23 as the models. It is known that the exposure of these peptides to water can be tuned by formation of the channel or pore in lipid membrane[36,37,38,39]
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