The 2.6 A resolution crystal structure of the full-length putative ribose 5-phosphate isomerase from Toxoplasma gondii ME49 in complex with DL-Malic acid was determined by single anomalous dispersion method. The protein consists of two domains. The N-terminal domain folds into a parallel 5-stranded beta-sheet, antiparallel 3-stranded beta-sheet and 5 helices. The C-terminal domain folds into an antiparallel 3-stranded beta-sheet and 4 helices. The antiparallel 3-stranded beta-sheet of the N-terminal domain is positioned at the interface of the two domains. Molecule of D-malate is bound to the protein at a surface exposed positively charged pocket located at the interface of the two domains. The PISA and crystal packing analysis revealed that the protein forms two types of dimers along two two-fold axes. One dimer has 3300 A2 and another 2400 A2 in total buried surface area. Further crystal packing analysis also revealed that protein is arranged in an octameric ring-like structure with large solvent channels (30+ Angstroms) along the four-fold axis.