Thermal motion in proteins at biological temperatures significantly influences quantum biological functions, particularly those sensitive to changes in the relative orientation of the relevant protein parts and to the speed and magnitude of intra-protein motion.
To quantify the impact of thermal motion, we developed a multi-scale computational approach combining all-atom molecular dynamics (MD) simulations, density functional theory (DFT)-based calculations, and Bloch–Redfield-Wangness spin dynamics for relevant protein parts involved in chemical reactions.
We previously studied the effects of thermal motion on the magnetic compass mechanism in migratory birds, which is thought to rely on a radical pair in cryptochrome photoreceptors. For the associated chemical reaction product to be influenced by the Earth's magnetic field, the radical pair must stay sufficiently long in a non-equilibrium coherent state, which is vulnerable to spin relaxation driven by thermal motion. Through analysis of cryptochrome dynamics, we quantified how various degrees of freedom affect the coherence lifetime of the radical pair, which influences the sensitivity of the bird's magnetic compass.
In a new project, we are investigating the role of thermal motion in exciton transfer within the light-harvesting system of cryptophytes. X-ray crystallography and cryo-EM are used to obtain the structures of phycobiliproteins in the antenna complex and of the light-harvesting system. The structures will then be used in MD simulations and quantum chemical calculations to understand how thermal motion affects exciton transfer dynamics in the system.