Figure 6. Cleavage of the βI disulfide increases βI-domain flexibility and stresses at the MIDAS site.

(A) Conformational distribution of the oxidized (left) and reduced (right) αIIbβ3 integrin apo headpiece along two major conformational modes as obtained from MD simulations, starting from the extended apo conformation (PDB code 3fcu). The color code shows the density of conformations, ranging from low (white) to high (dark blue) density (in arbitrary units). Disulfide reduction increases the covered area and, thus, the conformational fluctuations. (B–D) Allosteric signaling network upon reduction of the Cys177-Cys184 disulfide bond. Differences in Fpair-wise force between the oxidized and reduced integrin headpiece are shown as blue sticks for the indicated force cut-off values. Calcium and magnesium ions are presented as yellow and orange spheres, respectively, the β-propeller domain as the green cartoon and the βI-domain as the cyan cartoon. (E) Details of the Fpair-wise force difference network around the metal-binding sites in the βI domain. Stress intensity is indicated by the color spectrum as used for b-factors (spectrum ranging from 75 pN – 399 pN).

Figure 6—figure supplement 1. Cleavage of the βI disulfide results in increased βI domain flexibility and high stresses at the MIDAS site in the bent apo and extended holo αIIbβ3 structures.

Conformational distribution of the oxidized (left) and reduced (right) αIIbβ3 integrin, obtained from MD simulations, starting from the bent apo (A) and extended holo (C) conformation. The MD trajectories are projected along two major conformational modes, obtained from principal component analysis. The color code shows the density of conformations, ranging from low (white) to high (dark blue) density (in arbitrary units). Disulfide reduction increases the covered area and, thus, the conformational fluctuations. Allosteric signaling network upon reduction of the Cys177-Cys184 disulfide bond in the bent apo (B) and extended holo (D) conformations, recovered from force distribution analysis. Only pairs of residues for which the pair-wise force difference was larger than a 55 pN cutoff value are shown. Differences in pairwise forces are shown as blue sticks, calcium and magnesium ions as yellow and orange spheres, the β propeller domain as a green cartoon and the βI domain as a cyan cartoon. The peptide ligand is not shown. Stress intensity is indicated by the color spectrum as used for b-factors (spectrum ranging from 55 pN - 268 pN force difference between the oxidized and reduced integrin headpiece in (B) and from 55 pN - 165 pN in (C).