Direct visualization of polypeptide shell of ferritin molecule by atomic force microscopy

The polypeptide shell of the ferritin molecule has been imaged in water by atomic force microscopy (AFM). The central dip and the quaternary structure could be observed on the surface of the ferritin molecule anchored inhomogeneously in two dimensions. These structures observed in the AFM images are quite similar to the electron density map near the top of the apoferritin viewed down from a 4-fold axis structure reported previously (S. H. Banyard, D. K. Stammers, and P. M. Harrison, 1978. Nature (Lond.). 271:282–284). It has been achieved by introducing a "self-screening effect" of the surface charges of the AFM sample (S. Ohnishi, M. Hara, T. Furuno, and H. Sasabe. 1992. Biophys. J. 63:1425–1431) and the specially sharpened stylus of AFM cantilever.