Figure 5. Unfolding length statistics by AFM for dystrophin nano-constructs.

(A) Histograms for peak-to-peak unfolding lengths for R18~L1~R21, R16~L2~R21 and R15~L3~R23 all show a major peak that was fit with a Gaussian for single domain unfolding centered near ~20 nm. Peaks at ~2× and ~3× the major peak value reflect simultaneous unfolding of multiple repeats. (B) After the 6000–8000 contacts of tip to surface, the total unfolding length (avg. ± S.D.) beyond the second peak is obtained for each sawtooth, which is categorized by N_pk. The upper gray regions indicate the extension limits calculated from Table 2, and the slope of the best-fit line through all of the data (including zero total unfolding length at N_pk = 2) is the average distance between peaks, which accounts for both single and multi-domain unfolding‥ The lower bargraph shows frequency distributions of N_pk fitted to exponential decays of the form m^−Npk with 3 < N_pk < max(N_pk) and the indicated values for m.