coding sequence of Zymomonas mobilis QC (ZmQC) was cloned and expressed. The recombinant ZmQC shows QC activity and its 1.7Å resolution crystal structure confirmed its close relationship to the plant QC enzymes. The bacterial ZmQC protein exhibits a five β-propeller fold with a cation, presumably calcium, in its core. The β-propeller consists of a five-fold repetition of four stranded antiparallel β-sheets arranged around a central axis to form a central tunnel connecting both sides of the molecule. The propeller is stabilized through a ̈Velcro ̈ motif that tethers the toroidal structure but lacks any disulfide bridges present in the related plant enzymes. The putative active center of ZmQC, occupied in the crystal by a glycerol molecule, is lined by the residues E46, E90, W104, W130, W175, N175 and K244. The three trytophans form a square pocket juxtaposed by the other catalytically relevant residues E46, E90 and K244.