The Quantum Environment in Cryptochrome Enhances Light Absorption of FAD

Area of Science:

• Biophysics
• Quantum Chemistry
• Spectroscopy

Background:

• Cryptochromes are proteins vital for circadian rhythms and magnetoreception.
• Accurate spectroscopic calculations of cryptochromes are computationally expensive.
• Current methods typically focus quantum mechanics on a small chromophore region.

Purpose of the Study:

• To present a novel computational formalism for quantum-mechanical treatment of cryptochrome absorption spectra.
• To enable the inclusion of surrounding amino acids and cofactors in quantum calculations.
• To investigate the role of the protein environment in light absorption.

Main Methods:

• Utilized the real-time time-dependent Hartree-Fock (RT-TDHF) method.
• Extended the quantum mechanical treatment from dozens to over a thousand atoms.
• Incorporated neighboring amino acids, tryptophan residues, and the MTHF cofactor.

Main Results:

• Successfully computed absorption spectra with an expanded quantum mechanical domain.
• Identified specific regions responsible for light absorption at different wavelengths.
• Demonstrated that the FAD chromophore's environment amplifies light absorption within cryptochrome.

Conclusions:

• The developed formalism offers a more comprehensive understanding of cryptochrome photophysics.
• This method allows for species-specific environmental effects to be accurately modeled.
• The findings highlight the significant contribution of the protein microenvironment to cryptochrome function.