Fig. 3: Mechanical unfolding of the circular permutant of C1, C1CP.
From: An ester bond underlies the mechanical strength of a pathogen surface protein
a Structure of C1CP based on PDB (4MKM). b Topology of C1CP. Ester bond formed between T11 and Q141 is highlighted in cyan. The new N- and C-termini are at the position 126 and 125, respectively. The original N- and C-termini are connected by an ELP loop. c Representative force–extension curve of stretching (GB1)2-C1CP-(GB1)2 following the same experimental protocol shown in Fig. 1d. The force peaks with ΔLc of ~38 nm (green) and ~23 nm (orange) are assigned as the unfolding of C1CP and the rupture of ester bond, respectively. The force peaks of ΔLc of ~18 nm correspond to the unfolding of GB1 domains. d Schematic illustration of the contour length change upon stretching C1CP. First, the protein unfolds up to the ester bond position, then the rupture of ester bond releases the sequestered sequence. e Histogram of ΔLc for C1CP unfolding events peaks at 38 nm. f Unfolding force histogram of C1CP centers at 91.5 ± 52 pN (n = 243, total number of C1 unfolding events). The Monte Carlo simulation of the force distribution results in a Δxu of 0.25 nm and α0 of 0.37 s−1 (Supplementary Fig. 14). g Histogram of ΔLc corresponding to the rupture of ester bond in C1CP peaks at 23 nm. h Histogram of the rupture forces of ester bond centers at 77 ± 56 pN (n = 243, total number of rupture of ester bond events). This experiment was repeated three times independently with similar results. Source data are provided as a Source Data file.
