Typically, for sample preparation for AFM imaging, 200 μl of protein solution containing assembled structures was incubated on a mica surface for 30 min to allow sample deposition on mica surface. The excessive solution was then washed away twice with 200 ml of deionized water. The mica surface was dried through a constant flow of nitrogen gas and then immediately collected for AFM imaging. Tapping mode AFM was performed on an Asylum MFP-3D AFM (Asylum Research) using microcantilevers (k = 26.1 N/m and V = ~300 kHz). Data are presented in Fig. 2B and fig. S2A.