Mechanistic Insights on Heme-to-Heme Transmembrane Electron Transfer Within NADPH Oxydases From Atomistic Simulations

Verification of radical pair mechanism predictions for weak magnetic field effects on superoxide in planarians

Superoxide concentration and tissue regeneration in planarians exhibit a complex non-monotonic dependence on the strength of an applied weak magnetic field. While this is difficult to understand based on classical physics, a recently proposed quantum model based on a flavin-superoxide radical pair mechanism could replicate the previously observed superoxide concentrations. However, this model also predicts increased superoxide concentrations for both lower and higher fields. This seemed to conflict with earlier experimental observations on blastema sizes, which were correlated with superoxide in the previously observed regime but were known not to follow the predicted trends for lower and higher fields. Motivated by this apparent contradiction, we here directly experimentally tested the predictions of the quantum model for superoxide for lower and higher fields. To our own surprise, our experiments confirmed the predictions of the radical pair model for superoxide, and incorporating interactions with multiple nuclei further improved the model's agreement with the experimental data. While open questions remain regarding the exact relationship between blastema sizes and superoxide, which is revealed to be more complex than previously observed, and the detailed properties of the underlying radical pair, our results significantly support a quantum biological explanation for the observed magnetic field effects.

Structure of human phagocyte NADPH oxidase in the activated state

Phagocyte NADPH oxidase, a protein complex with a core made up of NOX2 and p22 subunits, is responsible for transferring electrons from intracellular NADPH to extracellular oxygen1. This process generates superoxide anions that are vital for killing pathogens1. The activation of phagocyte NADPH oxidase requires membrane translocation and the binding of several cytosolic factors2. However, the exact mechanism by which cytosolic factors bind to and activate NOX2 is not well understood. Here we present the structure of the human NOX2-p22 complex activated by fragments of three cytosolic factors: p47, p67 and Rac1. The structure reveals that the p67-Rac1 complex clamps onto the dehydrogenase domain of NOX2 and induces its contraction, which stabilizes the binding of NADPH and results in a reduction of the distance between the NADPH-binding domain and the flavin adenine dinucleotide (FAD)-binding domain. Furthermore, the dehydrogenase domain docks onto the bottom of the transmembrane domain of NOX2, which reduces the distance between FAD and the inner haem. These structural rearrangements might facilitate the efficient transfer of electrons between the redox centres in NOX2 and lead to the activation of phagocyte NADPH oxidase.