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

Visualizing the structure of the protein-inorganic interface is critically important for a 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-electron microscopy (cryo-EM) to study the protein-nanoparticle (NP) 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 NP 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.