Observation of the Protein-Inorganic Interface of Ferritin by Cryo-Electron Microscopy

Visualizing the structure of the protein-inorganic interface is critically important for our more complete understanding of biomineralization. Unfortunately, there are limited approaches for the direct and detailed study of biomolecules that interact with inorganic materials. Here we use single particle cryo-EM to study the protein-nanoparticle interactions of human light chain ferritin and visualize the high-resolution details of the protein-inorganic interface. In this work, we determined the 2.85 Å structure of human light chain ferritin bound to its native iron oxide nanoparticle substrate. The resulting cryo-EM maps confirmed and enhanced previously proposed interactions of the protein with the material along the B-helix, and revealed new interaction at the C-terminus of light chain ferritin. This work sheds new light on the mechanisms of ferritin biomineralization and further demonstrates the application of cryo-EM for the study of protein-inorganic systems. ### Competing Interest Statement The authors have declared no competing interest.