PMC

(a) Force-extension curves (offset for clarity) observed for fibrinogen oligomers (black) with simulated overlays (blue). The traces have two, five, and ten coiled-coil unfolding peaks from oligomers with at least one, three, and five fibrinogen molecules, respectively (each molecule has two coiled-coils). The last peaks are due to protein desorption as is the first large peak in the lowest trace. (b) Histogram of peak forces (bars) is well approximated by the simulated data (blue line). (c) Histogram of peak-to-peak distances with a major peak at 23 nm.

Transmission electron micrographs of fibrinogen monomers (a); di- (b); tri- (c); tetra- (d); and pentamers (e). The scale bar represents 50 nm. (f) The presence of the γ-γ band in SDS-PAGE confirms that the oligomers observed by TEM were covalently cross-linked. (g) Histograms of degree of oligomerization are plotted as the relative frequency of different species on a log scale. The fractionated sample contains only 6% monomer (solid bars, n = 291) compared to the unfractionated sample that contains 85% monomer (shaded bars, n = 1046).

(a) Schematic of the pulling geometry. Fibrinogen oligomers adsorbed on mica were extended by the AFM tip shown in yellow. If a single coiled-coil is unfolded, the oligomer contour length increases by 23 nm. (b) Crystal structure of an individual fibrinogen molecule () with two globular modules, γC and βC, at each end separated by two triple-helical coiled-coils confined between clusters of disulfide bonds (indicated by arrows). The force-propagating coiled-coils, γC-modules, and the central region are shown in red. The C-terminal portions of the Aα-chains are shown in blue with the αC-domains, not visualized in the crystal structure, represented as dotted blue lines.