The structure of the class II zinc-ion dependent L-fuculose-1-phosphat
e aldolase from Escherichia coli in its tetragonal crystal form has be
en established at 1.92 Angstrom resolution. The homotetrameric enzyme
has a molecular mass of 4 x 24 kDa and follows C-4 symmetry. The struc
ture model is exactly symmetrical, which contradicts an observed biref
ringence anomaly of the crystals. The four catalytic centers are locat
ed in deep clefts at the interfaces of adjacent subunits. The zinc ion
is coordinated by three histidines and one glutamate in an almost tet
rahedral arrangement. Tn contrast to numerous other catalytically comp
etent zinc ions, there is no water molecule in the ligand sphere. Repl
acement of zinc by a cobalt ion caused only small structural changes.
A search through the Protein Data Bank indicated that the chain fold i
s novel. Sequence homology searches revealed a significant similarity
to the bacterial L-ribulose-5-phosphate 4-epimerase.