Figure 1.
A) Ribbon diagram of the quaternary structure of TTR with a schematic representation of the three-related pairs of pockets capable of accommodate an iodine atom in each binding site located at the interface of monomers A–A′ and B–B′. These pockets are named in the literature HBP1-HBP1′ (green spheres), HBP2-HBP2′ (pink spheres) and HBP3-HBP3′ (blue spheres). B) Detailed view of one of the binding sites for the TTR:T4 complex, showing the occupation of four of the six HBPs by the iodine atoms of T4 .
Figure 2.
Affinity grids for the different halogens in TTR binding site.
Contour maps are drawn at the highest level in which the HBP regions are showed: −0.8 kcal/mol for fluorine (upper left), −2.8 kcal/mol for chlorine (upper right), −3.6 kcal/mol for bromine (bottom left) and −5.2 kcal/mol for iodine (botom right). The contouring of the maps has been done at different levels of energy to emphasize that que energy interaction values increases with the atomic number of the halogen.
Table 1.
Energy values (in kcal/mol) of the minima points of affinity grids regions corresponding to HBPs in the A–A′ binding site of TTR:T4 complex after removing T4 and water molecules (see materials and methods section for details).
Figure 3.
Effect of iodination: proof of concept.
Selected families in which iodination enhances inhibitory efficiency.
Figure 4.
Synthesis of diflunisal and iododiflunisal analogs.
A) Modifying functional groups of diflunisal; B) Conjugation to α-amino acids; and C) Conjugation to β-alanine derivatives.
Figure 5.
A) Diflunisal analogs: modifications in the salicylic ring; B) Diflunisal conjugates to α-amino acids; C) Diflunisal conjugated to β-alanine.
Figure 6.
Data from kinetic turbidity assay, T4 competition assays and binding selectivity for plasma proteins for compounds 1 to 14 (series a and b).
Figure 7.
Part II: Data from kinetic turbidity assay, T4 competition assays and binding selectivity for plasma proteins for compounds 15 to 23 (series a and b) and reference compounds T4, T3, T0, and TIP.
Figure 8.
TTR binding vs. aggregation inhibition.
TTR binding (from T4 displacement) vs. fibrillogenesis inhibition (from turbidimetric assay) plot for the series of iododiflunisal derivatives 1b–23b. Group 1 and group 2 inhibitors are marked (see text).
Figure 9.
TTR tetramer stabilization by inhibitors monitored by circular dichroism in 6M urea.
Influence of small molecule inhibitors diflunisal (1a, 7,2 µM DIF) and iododiflunisal (1b, 7,2 µM IDIF) on the rate of wtTTR (3,6 µM) (left) and mutant Y78FTTR (3,6 µM) (right) dissociation in 6M urea measured by Far-UV CD circular dichroism as a function of time.
Figure 10.
Ribbon diagram of the quaternary structure of TTR in complex with iododiflunisal-betaAlaOMe (23b) (A) and betaAlaOH (22b) (B) conjugates.
Because of the two-fold symmetry axis running along the hormone-binding channel there are two-symmetry related binding positions of the two compounds in each binding site.
Figure 11.
Crystal structures of the TTR-22b and TTR-23b complexes.
A) Close-view of the TTR hormone binding sites AA′ of the TTR:iododiflunisal-betaAlaOMe (23b) (in grey) and TTR:iododiflunisal-betaAlaOH (22b) (in blue) superposed. Only one of the two-symmetry related binding positions of these two iododiflunisal conjugates is shown. B) Superposition of the crystal structures of the TTR:iododiflunisal-betaAlaOMe (23b) (in grey), TTR:iododiflunisal-betaAlaOH (22b) (in blue), and TTR:iododiflunisal (1b) complex (in yellow).
Figure 12.
Superposition of TTR:iododiflunisal-betaAlaOH (22b) (blue) and TTR:iododiflunisal-betaAlaOMe (23b) (yellow) and TTR:T4 complexes (green).
Iodine in iododiflunisal derivates is in the same region as I3 of T4.
Figure 13.
Affinity grids maps for TTR:iododiflunisal-betaAlaOH (22b) (A) and TTR:iododiflunisal-betaAlaOMe (23b) (B) complexes.
Contour maps are drawn at −0.9 kcal/mol for fluorine and −6.3 kcal/mol for iodine. For clarity, only contour surrounding iodine and fluor substituents are shown and TTR structure is hidden. Iodine's contour is coloured in purple, fluorine countour coincident with HPB3 pocket is coloured in green, an the additional region located in the most inner part of the cavity along the two-fold symmetry axis is coloured in red.