The S. cerevisiae RpiA structure. A. Ribbon representation of the overall structure of the RpiA monomer. Secondary structure element labels correspond to those superposed on to aligned sequences in Fig. 4. B. Ribbon representation of the RpiA homotetramer. Monomer A is coloured as in Fig. 2A. Monomers B, C and D are coloured beige, grey and yellow. The D-4-phosphoerythronic acid inhibitor (ball and sticks with the phosphor atom coloured in green) has been modelled into the active site of RpiA monomer A by superimposition of the structure of the P. horikoshii RpIA enzyme inhibitor complex [7]. The molecular surface is shown in transparency. C. Mapping of the conservation of the residues among the RpiA enzymes at the surface of the homotetramer. Strictly and highly conserved residues are coloured red and orange, respectively. The D-4-phosphoerythronic acid inhibitor bound to the P. horikoshii RpiA enzyme is shown as ball and sticks. D. Interactions realized by the Arg189 side chain in the ScRpiA structure. One monomer is coloured in yellow, the second in orange.
| Function | Ribose-5-phosphate ketol-isomerase |
| Fold | ?/? fold |
| Resolution | 2.1 |
| Remarks | Two ?/? domains |
| PDB code | Not yet |
| Reference | To be published |
Ribose-5-phosphate isomerase A has an important role in sugar metabolism by interconverting ribose-5-phosphate and ribulose-5-phosphate. This enzyme is ubiquitous and highly conserved among the three kingdoms of life. We have solved the 2.1 A resolution crystal structure of the Saccharomyces cerevisiae enzyme by molecular replacement. This protein adopts the same fold as its archaeal and bacterial orthologs with two alpha/beta domains tightly packed together. Mapping of conserved residues at the surface of the protein reveals strong invariability of the active site pocket, suggesting a common ligand binding mode and a similar catalytic mechanism. The yeast enzyme associates as a homotetramer similarly to the archaeal protein. The effect of an inactivating mutation (Arg189 to Lys) is discussed in view of the information brought by this structure.
