Thioredoxin three-dimensional structure

FIGURE 2. Three-dimensional structure of conserved residues and the substrate GDP in the active site of E. coli protein R1 (A) (Eriksson et al., 1997), and proposed reaction mechanism for RNR (B), A turnover is initiated by long-range RTF between Tyrl22 in R2 and Cys439 in Rl, and completed by a reversal of this RTP (thin arrows). Oxidised Rl is reduced by the thioredoxin (Trx), or glutaredoxin system. 

Unlike thioredoxin, glutaredoxin, and DsbA, which possess only one thiore-doxin-like motif, P/PDO is the first protein disulfide oxidoreductase whose three-dimensional structure has been shown to contain two thioredoxin fold motifs with two active sites. Thus, P/PDO shows structural resemblance to PDI and PDI-like protein s. This structural feature suggests that P/PDO is probably not just a simple protein disulfide reductant like thioredoxin as described previously. It may belong to the growing family of PDI-like proteins. From a structural point of view, P/PDO may represent the simplest form of PDI. 

The two thioredoxin-like domains in PDI possess the same active site motif and display obvious sequence identities to each other (50%) and to thioredoxin (30%). However, in Pf PDO the similarities among the two structural units and thioredoxin are only apparent upon the comparison of their three-dimensional structures. As the two Pf PDO units have distinct active site motifs and show rather low sequence identities (<20%) to each other and to thioredoxin, one may assume that the two Pf PDO units might have evolved more divergently than the thioredoxin-like domains in eukaryotic PDI. This assumption, however, is not in line with the hypothesis that hyperthermophiles are the least divergent organisms, which may represent the closest living descendants of ancestral life forms. " As the origin... 

Because of its dithiol/disulphide exchange activity, thioredoxin determines the oxidation state of protein thiols. This small ( 12 kDa) protein is evo-lutionarily conserved between prokaryotes and eukaryotes from yeast to plants and animals. A characteristic feature of most thioredoxins is the presence of a conserved catalytic site Trp-Cys-Gly-Pro-Cys-Lys in a protrusion of the three-dimensional structure of the protein. The two cysteine residues of the site can be reversibly oxidies to form a disulphide bridge and, thereafter, ne re-... 

Soderberg B O, Three-dimensional structure of Escherichia coli thioredoxin-S2 to 2.8 A... 

As a first step toward the understanding of the regulation of pigment synthesis by oxygen in this bacterium, the amino-acid sequence of the Rb. sphaevoides Y thioredoxin and a three-dimensional model derived from the E, ooVl crystallographic structure have been previously reported (5). 

---