Recent Advances in Magnetosensing Cryptochrome Model Systems

Abstract

Although it has been widely and deeply studied for half a century that many animals sense the Earth's magnetic field for navigation, the exact mechanism of magnetoreception is still largely unclear. In 1978, Schulten et al. proposed that the radical-pair mechanism provides the operational principle of light-depended biological magnetoreception. This hypothesis has been developed in recent years, assuming that the flavoprotein and blue-light photoreceptor cryptochrome is the biological magnetosensitive molecule undergoing light-triggered radical-pair dynamics. Evidence is accumulating in favor of this radical-pair-based magnetoreception and the cryptochrome hypothesis. However, Complex in vivo and photochemical properties of cryptochrome hamper to identify the exact mechanism of biological magnetoreception. According to the radical-pair mechanism, magnetic fields may alter the rate and yields of chemical reactions involving spin-correlated radical pairs (SCRP) as intermediates. Such magnetic field effects (MFE) have been studied in detail in a variety of chemical systems both exper-imentally and theoretically. To improve the understanding of the radical-pair mechanism and the magnetosensitivity of cryp-tochrome, several artificial model systems have been constructed and studied by different analytical means. Model systems greatly simplify the complexity of the biological environment and allow for systematic variation of properties. Based on the research of domestic and foreign scholars, we here review studies on the radical-pair-based biological magnetoreception and magnetosensitivity of cryptochrome, and we discuss the recent progresses on three major artificial model systems:(1) a variety of flavin-based radical pair systems in mixture solution, micellar solution or protein environment; (2) chemical magnetosensitive model molecules, e.g. flavin adenine dinucleotide (FAD), a carotenoid-porphyrin-fullerene triad (C-P-F) and a flavin-tryptophan dyad (F10T); (3) artificial flavoprotein magnetosensors, i.e., a family of simplified, adaptable proteins-flavomaquettes. We also briefly summarize characteristics and advantages of those different artificial model systems and raise some key scientific issues in the further research on radical-pair-based biological magnetoreception.