PROJECT SUMMARY Mounting evidence suggests that magnetic fields may modulate important functions in cells. For example, magnetic fields can influence the spin state of photo-generated radical pairs in many flavoproteins, determining the rate of downstream reactions that govern cellular behaviors including circadian rhythms, DNA repair, and navigation of migratory birds. However, only low-to-moderate efficacy has been reported in clinical applications such as transcranial magnetic stimulation (TMS) and magnetotherapy, to treat epilepsy, depression and chronic pain. Improvement in treatment efficacy has been long stalled because the underlying molecular mechanism is poorly understood. This lack of progress is mostly due to not knowing the molecular mechanism of magnetic modulation. To measure the effective intracellular magnetic field to which biomolecules are exposed is the first step of building such understanding. The intracellular magnetic field is likely heterogeneous and not equivalent to the externally applied field of TMS or magnetotherapy, due to heterogeneous cellular compositions with varying magnetic permeabilities, as well as the heterogenous dynamic magnetic fields resulting from ion fluxes through ion channels. Currently no appropriate magnetometer exists to map the heterogeneous intracellular magnetic fields, though cellular measurement has been attempted using nitrogen a vacancy-center nanodiamond-based magnetometer, which can only provide sparse spatial readouts across the cell. Moreover, the necessity of subjecting cells to microwave radiation during nitrogen vacancy-center nanodiamond-based magnetometry is potentially harmful to cells. Herein we propose a genetically encoded magnetometer (GEM). GEM is a recombinant protein the backbone of which is a modified version of magnetosensitive flavoprotein. We will demonstrate that the heterogenous intracellular magnetic field can be mapped by expressing GEM in cells at unprecedented spatial resolution without the use of microwaves. If successful, GEM will enable the mechanistic study of TMS and magnetotherapy. In addition, it may also aid the evaluation of biological impacts due to pervasive presence of devices emitting electromagnetic waves.

PROJECT NARRATIVE Only low-to-moderate efficacy is reported in clinical applications of magnetic fields such as transcranial magnetic stimulation (TMS) and magnetotherapy, despite the experimentally proven fact that magnetic fields influence the spin state of photo-generated radical pairs in many flavoproteins which determine the rate of downstream reactions governing important cellular behavior. Improvement in treatment efficacy is limited due to not knowing the molecular mechanism of magnetic modulation and to the incapability to measure effective intracellular magnetic fields, which are likely heterogeneous and not equivalent to the externally applied field of TMS or magnetotherapy. To surmount the technical difficulty in intracellular magnetic field measurement, we propose a genetically encoded magnetometer (GEM) in the form of recombinant protein, with which we will demonstrate that heterogenous intracellular magnetic fields can be mapped by expressing GEM in cells at unprecedented spatial resolution.