Molecular Dynamics-Derived Coloured Noise Mediates Anderson Localisation and Environment-Assisted Transport of Tryptophan Excitons in Tubulin

This study investigates the quantum excitonic properties of the tryptophan network within tubulin $\alpha\beta$-dimers. Moving beyond traditional white-noise models (like the Haken-Strobl approximation), the author utilizes all-atom molecular dynamics (MD) simulations at 310 K to characterize the protein-solvent environment. By combining high-frequency (10 fs) and long-time (10 ps) sampling, the research captures a broad spectrum of environmental fluctuations, allowing for a microscopic derivation of the bath's statistical properties.

The analysis identifies three distinct relaxation modes in the site-energy autocorrelation function: sub-100-fs and picosecond fluctuations driven by water dynamics, and a nanosecond mode arising from protein conformational rearrangements. All three modes are found to be deeply non-Markovian. The slow protein-driven mode induces significant quasi-static disorder, leading to Anderson localization of excitons. Conversely, the faster water-driven modes provide the necessary resonance tuning to facilitate environment-assisted quantum transport (ENAQT). Notably, the study demonstrates that electrostatic anticorrelation between the protein and water effectively screens disorder, a mechanism that helps explain the high optical dielectric constant of tubulin.

When applied to the full eight-site tryptophan network, this coloured-noise model predicts that excitons are largely confined to strongly coupled proximal tryptophan pairs. This result contrasts sharply with the uniform delocalization predicted by standard white-noise models. The findings suggest that the tubulin environment is not merely a source of decoherence but an active participant in shaping energy transport, providing a more accurate, atomistically grounded framework for understanding quantum effects in biological systems.