Magnetically Probed Protein Interactions

Biomolecular radicals are of growing interest—for instance, some scientists speculate they are the basis for a magnetosensitive compass that guides migrating birds. But magnetic-field-sensitive phenomena have been observed in few biological systems. Now, Kiminori Maeda, Christiane R. Timmel, and coworkers at Oxford University have used the magnetosensitivity of photoinduced radical pairs as a probe of protein-substrate interactions (J. Am. Chem. Soc., DOI: 10.1021/ja908988u). Time-resolved absorption spectra of radicals generated from a tryptophan residue and an anthraquinone substrate, plus data on the dependence of radical concentration on magnetic field strength, showed that the substrate binds to the surface of hen egg white lysozyme but on the inside of a pocket in bovine serum albumin. Timmel notes that using a magnetic field to probe biomolecular radicals could make it possible to “learn about biomolecular dynamics, diffusion on surfaces, charge interactions, or surface potentials of biomolecules with a magnet no stronger than one you might find on your refrigerator.”