Decoding Structural Dynamics of Charge Transfer in Avian Cryptochromes by Time-Resolved Crystallography

forthcoming

Charge transfer is crucial in many biological processes, including photosynthesis, respiration, and DNA repair. While the kinetics of charge transfer are well studied, the associated protein structural dynamics that guide these reactions remain largely unexplored. This proposal aims to uncover, for the first time, the protein structural rearrangements that occur during charge transfer events, with a particular focus on avian cryptochromes involved in magnetoreception. Our primary objective is to reveal the structural response of two cryptochromes during charge transfer events using cutting-edge time-resolved serial crystallography (SX) at X-ray free-electron lasers (XFEL) facilities. We intend to elucidate the structure and dynamics of the radical pair state in non-magnetoactive ClCRY4 from non-migratory pigeon (Columba livia) (Objective 1) and magnetoactive ErCRY4 from night-migratory European robin (Erithacus rubecula) (Objective 2). Through comparative analysis of the two samples, we aim to identify the structural adaptations that correlate with their differing biological responses to magnetic fields. We hypothesize that highly directed structural rearrangements in proteins occur for stabilizing charge transfer states. This contrast current textbook knowledge. By focusing on radical pair states in cryptochromes, our comparative study between ErCRY4 and ClCRY4 will enable us to determine whether and how structural adaptations are aligned with their biological functions. This research is poised to make a significant impact in charge transfer theory, and will provide the first structural basis to understand magnetosensing in crpytochromes. We anticipate establishing a new paradigm in which protein structural fluctuations actively drive charge transfer reactions, and may reveal evolutionary optimizations in how cryptchromes have facilitated this for optimization of their sensing functions.