Physical limits to magnetogenetics

Abstract

This is an analysis of how magnetic fields affect biological molecules and cells. It was prompted by a series of prominent reports regarding magnetism in biological systems. The first claims to have identified a protein complex that acts like a compass needle to guide magnetic orientation in animals (Qin et al., 2016). Two other articles report magnetic control of membrane conductance by attaching ferritin to an ion channel protein and then tugging the ferritin or heating it with a magnetic field (Stanley et al., 2015; Wheeler et al., 2016). Here I argue that these claims conflict with basic laws of physics. The discrepancies are large: from 5 to 10 log units. If the reported phenomena do in fact occur, they must have causes entirely different from the ones proposed by the authors. The paramagnetic nature of protein complexes is found to seriously limit their utility for engineering magnetically sensitive cells.

Keywords: biophysics; magnetic control; magnetoreception; neuroscience; none; physical plausibility; structural biology.

Figure 1.. A TRPV4 channel (pink) inserted in the membrane with a ferritin complex (green) attached on the cytoplasmic side, approximately to scale.

The magnetic field B induces a moment m in the ferritin core, leading to a force F or a torque N on the ferritin particle, and resulting forces tugging on the channel. See text for details. DOI: http://dx.doi.org/10.7554/eLife.17210.003

Figure 2.. The steady-state temperature profile around a heated sphere in an infinite bath varies inversely with the distance from the center of the sphere.

The same argument applies to a ferritin sphere heated from its magnetic core (top) and a spherical cell with a large number of heated ferritins on its surface (bottom). DOI: http://dx.doi.org/10.7554/eLife.17210.004