Crystal structure of human thioredoxin revealing an unraveled helix and exposed S‐nitrosation site

Abstract

Thioredoxins reduce disulfide bonds and other thiol modifications in all cells using a CXXC motif. Human thioredoxin 1 is unusual in that it codes for an additional three cysteines in its 105 amino acid sequence, each of which have been implicated in other reductive activities. Cys 62 and Cys 69 are buried in the protein interior and lie at either end of a short helix (helix 3), and yet can disulfide link under oxidizing conditions. Cys 62 is readily S-nitrosated, giving rise to a SNO modification, which is also buried. Here, we present two crystal structures of the C69S/C73S mutant protein under oxidizing (1.5 Å ) and reducing (1.1 Å ) conditions. In the oxidized structure, helix 3 is unraveled and displays a new conformation that is stabilized by a series of new hydrogen bonds and a disulfide link with Cys 62 in a neighboring molecule. The new conformation provides an explanation for how a completely buried residue can participate in SNO exchange reactions.

Purification and characterization of Taenia crassiceps cysticerci thioredoxin: insight into thioredoxin-glutathione-reductase (TGR) substrate recognition

“…The crystallographic and modelled interactions of the two structures show the same complementary charges on the interacting face between Trx and TrxR. These results are in accord with previous studies in which the negative patch around the Trx α3 helix is used to make contact with the target molecules and TrxR [18,[78][79][80][81]. Moreover, in P. falciparum, it has been demonstrated that residues Asp58-Ser71 of Trx are bound to helical Pf-TrxR residues Ser136-Ser151 [59].…”

Protective effect of placenta extracts against nitrite-induced oxidative stress in human erythrocytes

“…The protective effect of this fraction may be explained by the presence in HPE of the antioxidant protein thioredoxin with molecular mass of 12 kDa. Thioredoxin is known to be implicated in S-nitrosation (also called S-nitrosylation) activities [20] and to play a significant role in antioxidant protection of erythrocytes [21]. Thus we suppose that extract proteins play a significant role in erythrocyte protection against nitrite-induced oxidative stress.…”

Dissection of the Water Cavity of Yeast Thioredoxin 1: The Effect of a Hydrophobic Residue in the Cavity

“…Because nonlocal water molecules may also contribute to the negative ratio 43 , observation of tightly bound water molecules is not in itself conclusive, e.g., for Asp24. However, it is conclusive for 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 thioredoxins at position 24 because it is well known that a tightly bound water is present in the crystal structures for the reduced and oxidized state, hydrogen-bonded to the carboxyl side chain of Asp24 [44][45][46] . Due to the reasons noted above, we limit our analysis to the solvation of this site.…”