Optical backbone-sidechain charge transfer transitions in proteins sensitive to secondary structure and modifications

Area of Science:

• Biophysics
• Computational Chemistry
• Spectroscopy

Background:

• Proteins absorb light, inducing charge transfer (CT) transitions in the UV-visible spectrum.
• Visible light absorption often involves metal-ligand complexes or prosthetic groups, while the protein backbone shows CT in the far UV.
• New near UV-visible CT transitions involving charged amino acids are explored.

Purpose of the Study:

• To computationally investigate new near UV-visible charge transfer (CT) transitions involving charged and phosphorylated amino acids.
• To analyze the electronic donor-bridge-acceptor paradigm in amino acids.
• To understand factors influencing CT transition spectra and direction.

Main Methods:

• Time-dependent density functional theory (TD-DFT) calculations.
• Analysis of absorption spectra for naturally charged and phosphorylated amino acids.
• Utilizing molecular dynamics simulations for protein structures.

Main Results:

• Charged amino acids exhibit a donor-bridge-acceptor electronic structure, leading to backbone-sidechain charge separation.
• The spectral range of these CT transitions depends on chemical composition, conformation, and protein secondary structure.
• Photoinduced charge separation is more efficient in anionic amino acids compared to cationic ones.

Conclusions:

• The findings support the development of spectroscopic markers, Protein Charge Transfer Spectra (ProCharTS).
• These markers are relevant for studying DNA-binding or intrinsically disordered proteins.
• The study elucidates the fundamental mechanisms of light absorption and charge transfer in proteins.