Abstact

The crystal structure of the human arginase I-thiosemicarbazide complex reveals an unusual thiocarbonyl μ-sulfide ligand in the binuclear manganese cluster. The C=S moiety of thiosemicarbazide bridges Mn2+A and Mn2+B with coordination distances of 2.6 Å and 2.4 Å, respectively. Otherwise, the binding of thiosemicarbazide to human arginase I does not cause any significant structural changes in the active site. The crystal structure of the unliganded enzyme reveals a hydrogen bonded water molecule that could support proton transfer between a μ-water molecule and H141 to regenerate the nucleophilic μ-hydroxide ion in the final step of catalysis.