Figure 1.

Imaging apo- and holo-transferrin conformations. (a) PDB models of apo- (PDB: 1RYX¹⁵) and holo-transferrin (PDB: 1JNF¹⁶). Transferrin molecules switch between the apo- and holo-forms by the binding and releasing of iron ions (indicated as red spheres in the holo-transferrin model). The associated conformational change manifests by the appearance of clefts in the lobes of apo-transferrin molecules.) b) One-step amplitude reconstruction of a hologram of an individual apo-transferrin molecule experimentally acquired by a LEEH measurement. On one of the lobes, the cleft defining the open lobe conformations is clearly visible, as indicated by the green arrow. Scale bar: 5 nm. (c) One-step amplitude reconstruction of a hologram of an individual holo-transferrin molecule experimentally acquired by a LEEH measurement. Scale bar: 5 nm. Insets in (b) and (c) show the experimental image superimposed by a projection of the PDB model in an orientation corresponding to that of the imaged molecule.