Figure 7.

Dark-field STEM mass analysis of T2i88-8-pf stepwise refolded at pH 7.0. The histogram displays the masses of 389 imaged nanoparticles calculated from their scattering power and corrected for beam-induced mass loss. Particles with masses in the different regions of the histogram (delimited by dotted lines) are shown in the inset; scale bar: 50 nm. The mass distribution could be described by fitting 5 Gaussian curves of equal width. While peaks 1 (1.9 ± 0.4 MDa, n = 35) and 2 (2.9 ± 0.4 MDa, n = 195) primarily arise from single nanoparticles often with almost circular projections, peaks 3 (4.2 ± 0.4 MDa, n = 54), 4 (5.4 ± 0.4 MDa, n = 47) and 5 (7.2 ± 0.4 MDa, n = 30) and the few higher mass particles seem to be the result of aggregation. According to the mass indicated by peak 2, most of the nanoparticles are composed of 195 ± 27 peptide chains (a single chain has a molecular weight of 14900 Da).