Structural Flexibility and Disassembly Kinetics of Single Ferritins using Optical Nanotweezers

Ferritin, a spherical protein shell assembled from 24 subunits, functions as an efficient iron storage and release system through its channels. Understanding how various chemicals affect the structural behaviour of ferritin is crucial for unravelling the origins of iron-related diseases in living organisms including humans. In particular, the influence of chemicals on ferritins dynamics and iron release is barely explored at the single-protein level. Here, by employing optical nanotweezers using double nanohole (DNH) structures, we examined the effect of ascorbic acid (reducing reagent) and pH on ferritins conformational dynamics. The dynamics of ferritin increased as the concentration of ascorbic acid approached saturation. At pH 2.0 ferritin exhibited significant structural fluctuations and eventually underwent a stepwise disassembly into fragments. This work, for the first time, tracked the disassembly pathway and kinetics of single ferritins in solution. We identified four critical fragments during its disassembly pathway, which are 22-mer, 12-mer, tetramer, and dimer subunits. Moreover, we presented the first single-molecule evidence of the cooperative disassembly of ferritin. Interrogating ferritins structural change in response to different chemicals holds importance for understanding their roles in iron metabolism, hence facilitating further development of medical treatments for the associated diseases.