Protein-water coupling tunes the anharmonicity of amide I modes in the interfacial membrane-bound proteins

• Published in: The Journal of chemical physics Vol. 156; no. 10; p. 105103
• Main Authors: Tan, Junjun, Ni, Zijian, Ye, Shuji
• Format: Journal Article
• Language: English
• Published: United States 14.03.2022
• ISSN: 1089-7690
• DOI: 10.1063/5.0078632

The diagonal anharmonicity of an amide I mode of protein backbones plays a critical role in a protein's vibrational dynamics and energy transfer. However, this anharmonicity of long-chain peptides and proteins in H O environment is still lacking. Here, we investigate the anharmonicity of the amide I band of proteins at the lipid membrane/H O interface using a surface-sensitive pump-probe setup in which a femtosecond infrared pump is followed by a femtosecond broadband sum frequency generation vibrational spectroscopy probe. It is found that the anharmonicity of the amide I mode in ideal α-helical and β-sheet structures at hydrophobic environments is 3-4 cm , indicating that the amide I mode in ideal α-helical and β-sheet structures is delocalized over eight peptide bonds. The anharmonicity increases as the bandwidth of the amide I mode increases due to the exposure of peptide bonds to H O. More H O exposure amounts lead to a larger anharmonicity. The amide I mode of the peptides with large H O exposure amounts is localized in one to two peptide bonds. Our finding reveals that the coupling between the amide I mode and the H O bending mode does not facilitate the delocalization of the amide I mode along the peptide chain, highlighting the impact of H O on energy transfer and structural dynamics of proteins.