D-ribulose-phosphate 3-epimerase from Francisella tularensis catalyses the conversion of D-ribulose 5-phosphate into D-xylulose 5-phosphate and is a part of the pentose phosphate pathway. This metabolic pathway is present in many bacteria and plants, but not animals, making proteins of this pathway a good target for the drug design.
Subunits fold in a TIM barrel structure (beta/alpha 8-barrel). A sequence comparison with homologous epimerases outlined the active center and indicated that all members of this family are likely to share the same catalytic mechanism. The substrate could be modeled by putting its phosphate onto the observed sulfate position (between strands beta-7 and beta-8) and its epimerized C3 atom between two carboxylates that participate in an extensive hydrogen bonding system.