Differentiating Holo-and Apoferritin on Surface by Atomic Force Microscopy Approach


  • Indian Association for the Cultivation of Science, Department of Biological Chemistry, Kolkata, 700032, India


Ferritin protein has been chosen as a model system, since it is a well-characterized protein for testing the suitability of the Single Molecule Detection (SMD) methods like Atomic Force Microscopy (AFM) in studying tertiary structure of proteins and further testing the ability of AFM to be useful as a structural biology tool. AFM has been applied to obtain information about the shape, dimension and the presence of electronically conducting area(s) of ferritin proteins on HOPG surface. In this report it is shown that iron-containing Holoferritin and iron-free apoferritin can be successfully differentiated on surface by AFM. At sub-nanometer resolution a hallow around most of the holoferritin molecules were observed in the AFM topographic images along with a bright central core, cross-section profiles for holoferritin molecules showed a protruded top consisting of three humps which possibly indicate the protein shell-metal core-protein shell situation. Atomic Force Spectroscopy (AFS) experiments revealed that Young's modulus of holoferritin molecules are greater compare to apoferritin indicating presence of a hard central iron core. Conductive probe AFS measurements showed holoferriitn molecules are more conductive in comparison to apoferritin signifying a semiconducting nature of the iron core.

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