Crystal structure of the wild-type and D30A mutant thioredoxin h of Chlamydomonas reinhardtii and implications for the catalytic mechanism.Menchise, V., Corbier, C., Didierjean, C., Saviano, M., Benedetti, E., Jacquot, J.P., Aubry, A.
(2001) Biochem.J. 359: 65-75
- PubMed: 11563970
- Primary Citation of Related Structures:  1EP7
- PubMed Abstract:
- NMR Solution Structure of an Oxidized Thioredoxin h from the Eukaryotic Green alga Chlamydomonas reinhardtii
Mittard, V.,Blackledge, M.J.,Stein, M.,Jacquot, J.,Marion, D.,Lancelin, J.M.
(1997) Eur.J.Biochem. 243: 374
Thioredoxins are ubiquitous proteins which catalyse the reduction of disulphide bridges on target proteins. The catalytic mechanism proceeds via a mixed disulphide intermediate whose breakdown should be enhanced by the involvement of a conserved buri ...
Thioredoxins are ubiquitous proteins which catalyse the reduction of disulphide bridges on target proteins. The catalytic mechanism proceeds via a mixed disulphide intermediate whose breakdown should be enhanced by the involvement of a conserved buried residue, Asp-30, as a base catalyst towards residue Cys-39. We report here the crystal structure of wild-type and D30A mutant thioredoxin h from Chlamydomonas reinhardtii, which constitutes the first crystal structure of a cytosolic thioredoxin isolated from a eukaryotic plant organism. The role of residue Asp-30 in catalysis has been revisited since the distance between the carboxylate OD1 of Asp-30 and the sulphur SG of Cys-39 is too great to support the hypothesis of direct proton transfer. A careful analysis of all available crystal structures reveals that the relative positioning of residues Asp-30 and Cys-39 as well as hydrophobic contacts in the vicinity of residue Asp-30 do not allow a conformational change sufficient to bring the two residues close enough for a direct proton transfer. This suggests that protonation/deprotonation of Cys-39 should be mediated by a water molecule. Molecular-dynamics simulations, carried out either in vacuo or in water, as well as proton-inventory experiments, support this hypothesis. The results are discussed with respect to biochemical and structural data.
Laboratoire de Cristallographie et Modélisation des Matériaux Minéraux et Biologiques, Groupe Biocristallographie, ESA 7036, Université Henri Poincaré-Nancy I, BP 239, 54506 Vandoeuvre-lès-Nancy Cedex, France.