The structure of the flexible arm of Thermotoga maritima tRNase Z differs from those of homologous enzymes

tRNA 3′-processing endoribonuclease (tRNase Z) is one of the enzymes involved in the 3′-end processing of precursor tRNAs and is a member of the metallo-β-lactamase superfamily. tRNase Z crystal structures have revealed that the enzyme forms a dimer and has a characteristic domain, named a flexible arm or an exosite, which protrudes from the metallo-β-lactamase core and is involved in tRNA binding. The refined structure of Thermotoga maritima tRNase Z has been determined at 1.97 Å resolution, revealing the structure of the flexible arm and the zinc-bound active site. The structure of the flexible arm of T. maritima tRNase Z is distinct from those of the Bacillus subtilis and Escherichia coli tRNase Zs. A comparison of the three tRNase Z structures revealed differences in the dimer orientation, which may be related to the unique cleavage-site specificity of T. maritima tRNase Z.