Fig. 2
Selected structures of poplar enzymes. In all these structures, β-strands are shown in blue, α-helices are in red, and connecting loops are in purple. a Cartoon representation of the overall fold of the dimeric Prx IIB (PDB number, 1TP9). b Cartoon representation of the overall fold of the dimeric Gpx5 in the reduced form (PDB number, 2P5Q). Note that, in the oxidized form, the formation of an intramolecular disulfide bond between Cys44 and Cys92 induces a large conformational rearrangement leading in particular to the complete unwinding of the α1 helix. By comparing both structures, you could note the similar architecture of the monomers and the characteristic double β-strand external to the central pleated β-sheet. c Cartoon representation of the overall fold of the plastidial methionine sulfoxide reductase A (PDB number, 2J89). The structure of the monomer in the reduced form is shown here. The positions of the sulfur atoms of the important cysteine residues are indicated by yellow spheres. Site-directed mutagenesis experiments coupled to activity assays indicated that the catalytic Cys46 forms a disulfide with Cys202 before its subsequent reduction by Cys196. It is clear that considerable conformational rearrangements are needed to bring the sulfur atoms close enough to form these disulfides. This may explain why we have been unable to get the 3D structure of oxidized forms. d Cartoon representation of the overall fold of the monomeric thioredoxin h4 under two different oxidized forms (PDB numbers 3D21, 3D22). The sulfur atoms of the cysteine residues of the disulfide bonds are shown in yellow spheres. Left panel, disulfide bond between Cys58 and Cys61; right panel, disulfide bond between Cys4 and Cys58. Lacking residues (7–15) are shown in an imaginary gray dashed loop for a better overview of the right panel structure. e, f Structural comparison of Grx C1 and Grx C4 dimers. In the Grx C1 structure, there is one homodimer containing a [2Fe-2S] ISC plus two additional monomers symmetrically positioned but bearing no ISC. GSH indicates an external glutathione molecule (shown in stick) and GS glutathione molecule covalently linked to the Fe2S2 center. Sulfur and iron atoms are represented, respectively, as yellow and red spheres. Grx C4 makes a homodimer with no ISC. The PDB number of Grx C1 is 2E7P, whereas no coordinates were deposited for Grx C4