FIGURE 10. Four views across the D–D interface as seen from increasing distance.

a, Close-up showing structural details of end-to-end abutment of fragments D in double-D: R, Arg275; Y, Tyr280; S, Ser300; Ca, calcium atoms; GPRP, Gly-Pro-Arg-Pro-amide ligands. The residues at the interface are coloured according to their nearest distances to residues on the other side of the crevice, red being shortest and greater distances shading toward green. b, More distant view showing Glu396 of molecule A and Gln398 of molecule B connected by a broken line denoting crosslink; CH₂O, carbohydrate. c, Even more distant view of fibrin double-D with hypothetical fragment E domain rooted on the two Gly-Pro-Arg ligands and straddling the interface of abutting D domains. d, Very distant view showing three molecules of double-D connected by hypothetical structures corresponding to full-sized fragments E and connecting segments to show required packing in protofibrils. A fibrin monomer made from two halves of the double-D structure and the hypothetical fragment E is shown at the bottom.