Figure 1.

Topographs of the HPI layer outer surface and force-extension curve recorded during retraction of the stylus after indenting the protein layer with a force of 2 nN. (A) Control AFM topograph of the outer surface before indentation. The hexameric cores with six V-shaped protrusions and emanating arms are clearly resolved. Both structural details have been previously observed by three-dimensional electron microscopy and AFM (17) and were confirmed more recently (18–20, 29). The distance between the core centers is 18 nm. (B) The force-extension curves acquired on the outer surface indicating the absence of adhesion forces. (C) The same surface area imaged after recording the force curve; no structural changes have occurred. The defect core on the left was used to align topographs C and A. Full gray-level range of the topographs corresponds to 2.5 nm.